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Making the Grade: Annual ASE P2 Test Prep


In this month's issue, we mostly only address the technical aspects of the test. But there are other questions that deal with other areas such as sales, communication and inventory management. To help you, read on about certain areas you should know.
p> A little more then three decades ago, the independent, non-profit National Institute for Automotive Service Excellence (ASE) was established. It's mission was and is simple: To improve the quality of automotive service and repair through the voluntary testing and certification of technicians, parts specialists, machinists and other professions related to the motor vehicle service industry.

There are currently some 420,000 ASE certified professionals working in the industry.

ASE provides no training, just the testing to prove that you know your stuff.

ASE (through a third party) administers this testing twice a year, in the Spring and in the Fall. The test dates for the Fall testing are November 13, 18 and 20 at some 700 locations around the country. Although the deadline for the Fall test has passed, information on registration and future testing can be found at


How Certification Works
There are several different parts specialist tests you can take, depending on the kind of skills you have. These tests are not as easy to pass as you might think. In fact, approximately one out of three test takers fails.

The four tests include:

  • Medium/Heavy Truck Dealership Parts Specialist (P1) - this test reflects the wide range of component systems that a dealership parts specialist must know, as well as communication, sales and inventory management skills.
  • Automobile Parts Specialist (P2) - this test addresses the wide range of skills and knowledge required to work competently in a retail or jobber parts store environment. This month's ASE Parts Specialists Test prep deals exclusively with this test.
  • Medium/Heavy Truck Aftermarket Parts Specialist (P3) - this is the newest parts specialist test ASE offers. This test reflects the specialization that exists in this segment of the aftermarket. This test was designed so that a candidate could be tested on communication, sales and inventory management. Then test takers must answer questions on the specific vehicle system of their choosing. Two vehicle systems, Brakes and Suspension/Steering, are now available to test takers. Other systems will be added in the future.
  • General Motors Parts Consultant (P4) - this test was developed with GMSPO to assess a candidate's knowledge required to work competently in a General Motors Dealership parts department.

After passing at least one exam, and after providing proof of two years of relevant work experience, the test taker becomes ASE certified. This certification is valid for five years, and then retesting is required.

In this month's issue, we mostly only address the technical aspects of the test. But there are other questions that deal with other areas such as sales, communication and inventory management. To help you, here are the areas you should know:

Store Operations
There are 10 questions in this area. Make sure you are able to perform the following tasks.

  • Calculate discounts, profits, percentages and pro-rated warranties.
  • Calculate special handling charges.
  • Identify and convert units of measure.
  • Determine alphanumeric sequences.
  • Determine sizes with precision measuring tools and equipment.
  • Perform money transactions (cash, checks, credit and debit cards).
  • Perform sales and credit invoicing.
  • Interact with management and fellow employees.
  • Understand the value of housekeeping skills (facility, work stations, and backroom).
  • Assist with training.
  • Identify potential safety risks; Demonstrate proper safety practices.
  • Identify proper handling of regulated and/or hazardous materials.
  • Identify potential security risks.
  • Identify industry terminology.
  • Understand the value of company policies and procedures.
  • Understanding the basic functions of tools and equipment used in automotive service.

Customer Relations & Sales
There are 11 questions in this area. Be sure you are able to:

  • Identify customer types and skill level.
  • Identify customer needs.
  • Provide information to customers.
  • Handle customer complaints and returns.
  • Acknowledge and greet customers.
  • Demonstrate proper telephone skills.
  • Obtain pertinent application information.
  • Present a knowledgeable and professional image.
  • Recognize the value of selling related items.
  • Identify product features and benefits.
  • Handle customer objections.
  • Balance telephone and in-store customers.
  • Promote store services and features.
  • Promote upgraded products.
  • Solve customer problems.
  • Close the sale.

Vehicle Identification
There are three questions in this area:

  • Locate and utilize VIN.
  • Locate production dates.
  • Locate and utilize component ID data.
  • ID body styles.
  • Use additional reference sources for interpreting component information.
  • Locate paint codes.

Cataloging Skills
There are seven questions that will test your knowledge of cataloging skills:

  • Locating the proper catalog and ID the right parts.
  • Obtain and interpret additional information such as footnotes and illustrations.
  • Use additional sources like interchange lists, tech bulletins and supplements.
  • ID catalog terminology and abbreviations.
  • Perform catalog maintenance.

Inventory Management
There will be two questions on inventory management, including:

  • Lost sales reports.
  • Verification of outgoing and incoming merchandise.
  • Physical inventories.
  • Stock rotations.
  • Special orders.
  • Core handling.
  • Proper handling of returns and warranties.
  • Determining the proper selling units (each, pair, case, etc.)
  • Handle the return of broken kits, special ordered parts and exchanges.
  • Account for store use items.

There will be two questions on merchandising:

  • Display strategy.
  • Display pricing.
  • How to inspect and maintain shelf quantities and condition.
  • Impulse and seasonal items.
  • Sales aids.

Technical Areas
What follows are 13 articles that are based on technical areas of the ASE P2 Task List. Keep your pencils sharpened, keep your eyes on your own paper and good luck!


Editor's Note: There will be two questions on the P2 test that deal specifically with automatic transmissions.

An automatic transmission shifts itself using engine rpm, load and other inputs to regulate shift points and gear engagement. Older automatics have mechanical/hydraulic controls, while newer automatics have electronic/ hydraulic controls and are operated by a computer (the powertrain control module or a separate transmission control module). All automatics require some type of oil for the hydraulics as well as lubrication. Due to the complexity of the transmission, internal failures typically require replacing the entire transmission or transaxle with a new or remanufactured unit. Except for gaskets and filters, most internal transmission parts are dealer only parts.


The valve body is located inside the transmission oil pan and regulates gear shifts and clutch pack engagement. Other shift controls on some transmissions include a vacuum modulator and/or governor (used on older transmissions to modify the rpm at which the transmission upshifts when the vehicle is accelerating under load). The modulator is mounted on the side of the transmission and is connected by a vacuum hose to the intake manifold on the engine. Problems with either component will affect shifting. Older transmissions may also use a throttle cable or linkage for kickdown shifts when accelerating. Newer transmissions use shaft and vehicle speed sensor inputs and engine sensor inputs to regulate shifting.

Automatic Transmission Fluid (ATF) is the working fluid inside an automatic transmission. It lubricates the gears, bearings and bushings, carries hydraulic pressure to shift the gears and serves as a fluid coupling inside the torque converter to transfer engine torque to the transmission. The fluid level inside the transmission must be maintained between the FULL and ADD marks for proper transmission operation. The fluid should also be changed if it shows signs of oxidation (dark discoloration or burned odor) or at the interval recommended in the owners manual.

ATF is a lightweight mineral oil that contains special additives and friction modifiers. It is dyed red to distinguish it from motor oil. Different types of ATF are required for different makes and models of transmissions, so make sure your customer gets the correct type of fluid for his vehicle. Using the wrong ATF can cause shift problems and may damage the transmission.

GM, Ford, Chrysler, Honda, Mercedes and others all have their own specifications for ATF. There's no such thing as a "universal" ATF that works in all transmissions. Some fluids meet a variety of specifications but cannot meet them all because of the different friction additives that are required.

Ford has three automatic transmission fluid specifications: Type F (a non-friction modified formula for most 1964-81 transmissions), Mercon (a friction-modified ATF similar to Dexron II for 1988-97 transmissions) and Mercon V (Ford's latest friction-modified formula, introduced in 1997).

General Motors has two specifications: Dexron II and III. Both are friction-modified formulas and Dexron III can be used in the older GM transmissions that originally required Dexron II.

Chrysler has a number of different ATFs: MS-7176D (also known as ATF+2) is Chrysler's version of a friction-modified ATF that's similar to Dexron II. But Chrysler's fluid is more slippery than GM's, so Chrysler recommends using only ATF that meets their specifications in Chrysler transmissions. In other words, do not use Dexron or Mercon in a Chrysler transmission.

Chrysler MS-7176E (also known as ATF+3) was introduced in 1998 and supersedes ATF+2. It should only be used in 1998 and newer Chrysler transmissions, but it can also be used in earlier Chrysler transmissions. Chrysler ATF+4 is for 2000-01 model-year applications, and their newest fluid ATF+5 is for 2002 and newer models.

Located inside the transmission pan, the ATF filter traps wear particles that could damage the transmission. The filter should be replaced when the fluid is changed. A new transmission pan gasket is also required.


Original equipment ATF coolers are usually located in the bottom or the side of the radiator and are connected to the transmission with a pair of lines. Fluid circulates from the transmission to the cooler to maintain and limit the temperature of the ATF. For towing or hard use, installing an aftermarket auxiliary ATF cooler can help keep ATF temperatures down to prolong the life of the fluid and transmission.


The torque converter is a fluid coupling mounted on the flywheel between the engine and transmission that transfers engine torque to the transmission and also provides "torque multiplication" much like a set of reduction gears. Inside is a three-piece set of closely spaced blades, the turbine, stator and impeller. As the torque converter rotates, fluid is thrown from one set of blades against the other, much like a propeller churning water. This pushes the blades connected to the transmission input shaft and planetary gears to drive the vehicle down the road. Torque converters in most newer vehicles have a "lockup clutch" that engages in 3rd and 4th gears to eliminate slippage for improved fuel economy. The lockup clutch is engaged hydraulically and controlled by an electronic solenoid valve. The torque converter holds approximately one third of the total fluid required by the transmission. A failure results in slugging acceleration.

The transaxle is a transmission in a front-wheel drive car or minivan. A transaxle combines the transmission and differential into one unit.


Editor's Note: There will be three questions on the P2 test that deal specifically with brakes.

The brake system includes the master cylinder, power booster, disc brake calipers and rotors, wheel cylinders and brake drums, brake hardware, brake hoses and lines, various valves, disc brake pads and drum shoes and brake fluid. On vehicles equipped with antilock brakes (ABS), additional parts include up to four wheel speed sensors, the ABS hydraulic modulator and control module, and a pump motor and accumulator (not used on some systems).

When the driver steps on the brake pedal, it moves a rod in the master cylinder forward to push a pair of pistons against fluid in the primary and secondary chambers. Brake systems are split into two separate hydraulic circuits. Each circuit operates two of the four brakes (both fronts, both rears or a diagonal pair). This is a safety requirement so if one circuit fails, at least two brakes will continue to operate so the vehicle can be stopped.

Brake fluid carries the hydraulic pressure created in the master cylinder through the brake lines to the front calipers and rear calipers or drums to apply the brakes. Most older vehicles have front disc brakes and drums in the rear, but many newer cars, SUVs and trucks have disc brakes front and rear. When pressure reaches the brakes, the pads are squeezed against the rotors, and if the vehicle has drums in the rear, the shoes are pushed out against the drums to generate friction and stop the vehicle.

On vehicles equipped with power brakes, a brake booster located behind the master cylinder on the firewall multiplies the force of the brake pedal input using engine vacuum and a large diaphragm. This reduces the pedal effort needed to stop the vehicle. On some older vehicles with integral ABS systems, the ABS pump and accumulator provide power assist.

Additional parts involved in the braking process include a pressure differential valve (a safety switch that turns on the brake warning lamp if there's a loss of pressure in either brake circuit), a proportioning valve to reduce pressure to the rear brakes for more balanced braking (not used on all vehicles) and on some a load-sensing proportioning valve to increase or decrease hydraulic pressure to the rear brakes based on vehicle loading.

The major wear components in the brake system are the disc brake pads and drum shoes. Every time the brakes are applied, these parts are subjected to friction and wear.

Lining life depends on how the vehicle is driven. Stop-and-go city driving, mountain driving and aggressive driving all involve more frequent braking, harder braking and higher brake temperatures - all of which adds up to more wear and shorter lining life. Highway driving and gradual, light braking produce less lining wear and longer lining life.

On most vehicles, the front linings wear out twice as fast as the rear linings, so when the linings need to be replaced for the first time, it's usually only the front pads that need to be changed. Replacement linings should be the same or better than the original linings. Semi-metallic linings are often used in high-heat applications because they can withstand high operating temperatures without fading or wearing excessively. Other high-temperature friction materials include linings with ceramic content. Pads and shoes with nonasbestos organic (NAO) linings are typically used for lower-heat applications such as rear brakes and front brakes on rear-wheel drive cars and trucks.

When linings are replaced, the rotors and drums may need to be resurfaced or replaced depending on their condition. If a rotor is worn to minimum thickness, or a drum is worn to maximum diameter, replacement is necessary. Most rotors are made of cast iron, but composite rotors have a thin, stamped steel center hat attached to a cast iron rotor ring. Composite rotors are more difficult to resurface and more prone to pedal pulsation problems than one-piece cast rotors. They are also more expensive than cast. Composite rotors can be replaced with cast rotors as long as both rotors are replaced at the same time (don't intermix different kinds of rotors side to side).

Most front rotors are vented, while most rear rotors are not because more cooling is usually needed for the harder-working front brakes. Most rotors are interchangeable left to right, but some are directional, so pay close attention to the catalog listings when looking up part numbers. New rotors are ready to install and do not require additional resurfacing (turning rotors unnecessarily shortens their service life).

Other parts that wear out over time include hydraulic components such as the calipers, wheel cylinders and master cylinder.


Most calipers have one or two pistons, but some have up to four pistons mounted in a rigid housing. Most calipers are cast iron (though some are aluminum) with steel or molded phenolic (plastic) pistons. Most calipers are a floating design with slides or bushings that allow the caliper to move sideways and center itself over the rotor when the brakes are applied. Others are a fixed design with rigid mounts and do not move. If the slides or bushings on a floating caliper become badly corroded or worn, it may prevent the caliper from sliding, causing uneven pad wear. The inside pad will wear faster than the outside pad. If a piston in either type of caliper sticks, the caliper may not release, which can cause the brake to drag, rapid pad wear on one side, uneven braking and a pull to one side when the brakes are applied. Leaky piston seals will allow brake fluid to contaminate the brake linings. Leaky calipers must be rebuilt or replaced. Loaded calipers come ready to install with new pads. Bare calipers do not include pads. On vehicles with four-wheel disc brakes, the rear calipers may also include some type of parking brake mechanism. This makes the calipers more complicated and expensive to replace.


The wheel cylinders inside drum brakes have two opposing pistons that move outward when pressure is applied. The wheel cylinder is mounted on the brake backing plate, and has dust seals over the pistons to keep out dust and water. Each piston has a cup-shaped seal for the fluid inside. Common problems with wheel cylinders include fluid leaks and sticking. Wheel cylinders can be rebuilt or replaced. Leaking fluid can contaminate the brake shoes, requiring their replacement as well.

Wear in the master cylinder may allow fluid to leak past the piston or shaft seals. A symptom of a bad master cylinder is a brake pedal that slowly sinks to the floor when braking at a stop light. Leaks or failure to hold pressure require rebuilding or replacing the master cylinder. Rebuilding aluminum master cylinders is not recommended. On some older vehicles with ABS, the master cylinder is part of the ABS modulator and is very expensive to replace.

Rubber brake hoses can also deteriorate with age and leak. Any hose that is cracked, bulging, leaking or damaged should be replaced without delay because of the danger of brake failure should the hose leak. Steel brake lines can corrode internally or externally. Replacement brake lines must be steel with double-flared or ISO end fittings.


Brake fluid also wears out over time and should be replaced when the brakes are serviced.

The main issue here is moisture contamination that causes a breakdown of corrosion inhibitors in the fluid and lowers the fluid's boiling temperature (which increases the risk of fluid boil and pedal fade under hard use). DOT 3 and DOT 4 brake fluid are the two main types and both are glycol-based hydraulic fluid. DOT 5 fluid is a silicone-based fluid and is used only for special applications (like older vehicles that sit for long periods of time or are operated in extremely wet environments). DOT 4 has a higher temperature rating than DOT 3 and is used in many European vehicles. Use the type of fluid specified by the vehicle manufacturer.

Related items that may also need to be replaced when servicing the brakes include the wheel bearings and seals. On older vehicles with serviceable wheel bearings, the grease seals should always be replaced when the bearings are cleaned and repacked with grease. Special high-temperature wheel bearing grease is required (never ordinary chassis grease).

Disc and drum brake hardware should also be replaced when the brakes are serviced. Drum hardware includes the return springs, holddown springs, self-adjusters and other cables, clips or springs used in the brake assembly. Return springs that pull the shoes back away from the drum when the brakes are released may become weak with age, allowing the brakes to drag. Self-adjusters can become corroded and stick, causing increased pedal travel as the shoes wear. On disc brakes, the hardware includes slides and bushings that can become worn and corroded and anti-rattle clips and springs that reduce noise. A high-temperature, moly-based brake grease should be used to lubricate slides, bushings and shoe pads on drum brake backing plates.


Editor's Note: There will be two questions on the P2 test that deal specifically with cooling systems.

The cooling system includes the radiator, radiator cap, coolant reservoir, fan, water pump, thermostat, hoses, belts and antifreeze. Related parts include the coolant sensor and fan relay.

The radiator's job is to cool off the hot coolant after it leaves the engine block. The radiator is mounted up front so it gets good airflow when the vehicle is moving. But when the vehicle is stopped or traveling at low speed, additional airflow must be provided by a belt-driven or electric fan. The fan also operates when the A/C is on.

The radiators in most late-model vehicles are aluminum with plastic end tanks. Most older vehicles have copper/brass radiators. Both types are vulnerable to internal corrosion caused by coolant neglect. Leaks can sometimes be stopped by adding a sealer product to the coolant, but eventually the radiator will have to be repaired or replaced if it is leaking. Replacement radiators should have the same cooling capacity (or better) as the original and the same hose connections. Cooling capacity is determined by the thickness of the radiator, the number of fins and tubes and/or the design of the fins and tubes. Increased cooling capacity is recommended for towing and performance applications.

Connected to the radiator by a tube or hose is a plastic coolant reservoir. The reservoir typically holds up to a quart of coolant and prevents the loss of coolant if the engine overheats. The coolant level is maintained at the reservoir (never open a hot radiator cap!)

The radiator cap seals the radiator and pressurizes the coolant inside. This raises the temperature at which the coolant normally boils for added boilover protection during hot weather. System pressure ratings vary from five to 15 psi. A weak spring in the cap or a leaky seal can allow coolant to escape from the radiator, which may lead to overheating. Pressure testing the radiator cap will reveal its condition. If the cap can't hold its rated pressure, it must be replaced with one that has the correct pressure rating for the application.

The water pump is the heart of the cooling system. It circulates coolant between the engine and radiator to keep the engine at normal operating temperature. The pump is belt-driven and consists of an impeller mounted on a shaft inside a cast or stamped steel housing. The pump is usually mounted on the front of the engine. On some overhead cam (OHC) engines, the pump is mounted under the timing belt and requires considerable labor to replace. For this reason, you should recommend replacing the pump if the timing belt is being replaced for scheduled maintenance (recommended every 60,000 to 100,000 miles depending on the application.) The service life of the water pump and timing belt are about the same, so changing both at the same time can save the vehicle owner money on future repairs. Water pumps don't last forever, and leaks around the pump shaft seal and bearing can quickly lead to overheating. Any water pump that is leaking, making noise or has excessive shaft play should be replaced. Replacement options include remanufactured and new pumps.

The water pump may also be driven by a V-belt or a flat serpentine belt. The same belt may also drive other engine accessories. Belts deteriorate with age and should be replaced if frayed, cracked, glazed or oil-soaked. Replacement belt length and width must be the same as the original. On vehicles with serpentine belts, the automatic tensioner may also need to be replaced if it's sticking, making noise or cannot maintain proper belt tension. Belt idler pulleys should also be replaced if noisy, worn or sticking.

For temperature control, the cooling system requires a thermostat. It is usually located in a housing where the upper radiator hose connects to the engine. The thermostat does two things: it allows the engine to warm-up quickly (which reduces cold emissions and fuel consumption) and to maintain a consistent operating temperature (also important for low emissions, good fuel economy and performance). The thermostat has a temperature-sensitive valve that remains closed and blocks the flow of coolant until the engine reaches 195 to 210 degrees. It then opens and allows coolant to flow to the radiator. The thermostat continues to cycle open and shut so the engine will run within a certain temperature range. This is very important on late-model vehicles with computer engine controls because engine temperature affects the fuel feedback control loop, emissions, fuel economy and performance.

If the thermostat sticks shut, the engine will overheat. If it fails to close, the engine will be slow to warm-up, and the heater may not put out much heat when the weather turns cold. Fuel economy, emissions and engine wear will also suffer. Under no circumstances should an engine be run without a thermostat. Replacement thermostats should have the same rating as the original. A slightly hotter thermostat may be used during cold weather for increased heater output, but a colder thermostat should not be used on engines with computer controls. Other items that may be needed when changing a thermostat include a new thermostat housing and gasket or sealer.

To improve cooling, a fan is needed to pull air through the radiator when the vehicle is stopped or traveling at low speed. Older, rear-wheel-drive vehicles may have a belt-driven fan with or without a clutch. The clutch allows some slippage and is used to reduce fan noise at high rpm and to improve fuel economy by reducing drag. Excessive slipping in the clutch, however, may reduce airflow and cause the engine to overheat at low speed. Most newer vehicles have one or two electric cooling fans mounted behind the radiator, and a few have hydraulic fans driven by power steering fluid. Electric fans are powered through a relay and controlled by a coolant temperature switch or the engine computer. A failure of the fan motor, fan relay, coolant temperature switch or a wiring problem that prevents the fan from coming on can cause the engine to overheat.

The major hoses in the cooling system include the upper and lower radiator hoses (the lower one usually attaches to the water pump, and the upper usually attaches to the thermostat housing), plus a pair of heater hoses (one inlet and one outlet) and various connecting hoses and bypass hoses depending on the application. Original equipment hoses are usually molded (preformed) to fit a particular vehicle. Aftermarket replacement hose may be molded (which sometimes requires cutting to length), or straight or ribbed (flexible) to fit a wider variety of applications. Replacement hoses must be the same length and diameter as the original. New clamps should also be installed when hoses are replaced. Hoses should be replaced if leaking, cracked or bulging. Electro chemical degradation (ECD) due to coolant neglect can cause hoses to fail from the inside out.

The coolant that carries heat from the engine to the radiator is a mixture of ethylene glycol antifreeze and water (typically a 50/50 mix.) This combination provides freezing protection down to -34 degrees F and boilover protection up to 265 degrees F with a 15 psi radiator cap. The condition of the coolant is just as important as the strength because corrosion can attack the system from within if the coolant is neglected. The recommended replacement interval for traditional green antifreeze is two years or 30,000 miles. For the newer long-life coolants, the change interval can be as long as five years or 150,000 miles. Most long-life coolants use organic acid technology (OAT) additives that are different from those used in standard antifreeze. Long-life coolants may contain special dyes to distinguish them from ordinary antifreeze. General Motor's Dex-Cool is dyed orange, for example. Different types of antifreeze should not be intermixed as doing so may reduce the ability of long-life products from protecting the cooling system from corrosion.


Editor's Note: There will be two questions on the P2 test that deal specifically with drive train components. These components include driveshafts, half shafts, U-joints, CV joints and four-wheel drive systems.

The drivetrain consists of everything between the transmission and wheels. On rear-wheel-drive (RWD) cars and trucks, this includes the driveshaft, universal joints, differential and axles. On front-wheel-drive (FWD) cars and minivans it includes the halfshafts, constant velocity joints (CV) and hub assemblies, and on all-wheel-drive (AWD) cars and SUVs and four-wheel-drive (4WD) trucks, it includes a transfer case.

The most often replaced drivetrain components on RWD vehicles are the U-joints. On FWD vehicles, it's the CV joints. Both are components that eventually wear out.

U-joints are mounted on both ends of the driveshaft on RWD vehicles so the driveline can move up and down to follow the motions of the suspension. Each U-joint consists of a four-point center cross with needle bearing cups mounted in a pair of yokes. Vehicles with two-piece driveshafts have additional U-joints and/or a CV joint where the two shafts are joined and supported by a center carrier bearing.

U-joints are "phased" (positioned) 90 degrees to one another to reduce driveline vibrations. Almost all late-model OE U-joints are sealed, but some older vehicles have grease fittings for extended life. Some aftermarket replacement U-joints are also available with grease fittings for customers who want them. A worn U-joint may cause a vibration at speed or make chirping noises, or produce a clunk when putting the transmission into gear. Replacing a U-joint usually requires using a press to remove and install the joint from the yoke.

U-joints are not used on front-wheel drive applications because they can't handle large operating angles. CV joints are needed for this purpose. Each halfshaft will have a CV joint on each end (one inboard joint and one outboard joint). Outboard joints are designed to handle wider operating angles so the wheels can steer, while inboard joints are designed to plunge in and out so the driveline can follow the motions of the suspension.

Basic types of CV joints include Rzeppa, crossgroove, double-offset and tripod. ALl except tripod joints have six small balls housed between and inner and outer race. A cage with windows holds the balls in position as the joint flexes. Rzeppa CV joints are most often used as the outer joints on the halfshafts. Crossgroove and double-offset joints can "plunge" in and out and are often used as inner joints on halfshafts. Tripod joints contain no balls but have three roller bearings mounted inside a tulip- or claw-shaped housing. Tripod joints may be fixed or the plunging variety. Tripod CV joints are mostly used as the inner plunge joints on domestic FWD applications, but may also be used as outer joints on certain import applications.

CV joints require special grease that is packed inside the joint and sealed up with a protective rubber or plastic boot. Boot damage can allow loss of grease and joint contamination with dirt or water, leading to joint failure. Damaged boots should be replaced immediately, but are often not discovered until the joint has lost its grease or been contaminated by dirt or water. A typical symptom of a failing CV joint is a clicking or popping sound when turning. Failing inner joints may cause a clunk or vibration when accelerating. CV joints may be replaced separately or as part of a complete halfshaft assembly.

Replacement joints must have the same number of splines as the original and the same length and diameter input or hub shaft. On vehicles with ABS, there may also be a wheel speed sensor ring on the housing that must match the original.

Complete halfshaft assemblies are a popular repair item because they are easier to install than individual joints and reduce the risk of comebacks for the installer. Shafts are available with new joints, remanufactured joints or both.

The driveline also includes wheel and/or axle bearings at all four wheels to reduce friction. On older vehicles, the bearings are serviceable and require periodic inspection, cleaning and repacking with special wheel bearing grease (never ordinary chassis grease). The components include inner and outer bearings and races, a grease seal and a hub nut, locking ring and cotter pin. A new grease seal and cotter pin should always be installed when the bearings are serviced. Worn or loose wheel bearings can cause steering wander and noise.

The wheel bearings on most newer vehicles are sealed and do not require any maintenance or adjustment. The bearings are part of the hub assembly, which may also include the ABS wheel speed sensor on some vehicles. On FWD cars, a high-torque hub nut is used to hold the outer CV joint in the hub assembly. Nuts that are staked in place should be replaced if removed to service other parts.

On RWD and 4WD cars and trucks with solid axles, the outer ends of the axle shafts are supported by bearings located inside the lip of the axle housing. The bearings are lubricated by gear oil in the rear end. Replacement is required if the bearings are making noise, are loose or feel rough when the wheel is spun by hand. Bearings are press fit on the axle, which requires removing the axle to replace them.

Driveline lubricants include chassis grease for U-joints, CV joint grease for CV joints, wheel bearing grease for wheel bearings, and gear oil for differentials, manual transmissions and transaxles (typically 85W-90, 75W-140, etc.) Some transaxles use ATF instead of gear oil as a lubricant.

Differentials with "Posi-Traction" or limited-slip require a gear oil with special additives. It's important to follow the manufacturer's viscosity recommendations. Synthetic gear oils are popular because they flow more easily at low temperatures and reduce friction.

On AWD and 4WD vehicles, a transfer case located behind the transmission connects the front and rear drivetrains. Inside is a heavy steel chain or belt that carries torque to the front axle. The case is usually filled with gear oil or ATF. Operation may be manual or electronic.


Editor's Note: There will be two questions on the P2 test that deal specifically with electrical systems.

Electrical system parts include large rotating electrical components such as alternators and starters, solenoids, relays, batteries, battery cables, wiring, fuses, bulbs and small electrical motors for things such as power windows and seats.

Of all these parts, batteries are probably the most often replaced component. Average battery life is about four to five years in most areas of the country, and only about three years in really hot climates. Heat is hard on batteries because it increases evaporation of water from the cells. Maintenance-free batteries normally do not require additional water, but in hot climates water loss can be a problem. Most people don't check their batteries anymore, and on sealed-top batteries there are no caps to remove. Consequently, battery life suffers.

If a customer needs a new battery, recommend upgrading to a gel-type battery that contains no liquid water. The electrolyte is a gel-like substance sandwiched between absorbent fiberglass mats in the cells - making the batteries spill-proof and more resistance to heat damage. High-density spiral-wound batteries also use this same type of gel electrolyte.

Each cell inside a battery produces a little over two volts of electricity. Automotive batteries contain a total of six cells, so the total voltage is about 12 volts. A fully charged battery will actually read about 12.6 volts if you place a voltmeter across the terminals.

Post configurations will vary depending on the application. Most General Motors batteries have flat terminals on the side to which the positive and negative cables are attached with bolts. Everybody else uses batteries with two top posts (one negative and one positive.) Some aftermarket universal replacement batteries have both types of posts (top and side) to reduce the number of different batteries needed to cover vehicle applications.

Batteries come in different lengths, heights, widths and post configurations, which are classified according to group sizes. A replacement battery must be a compatible group size to physically fit the battery tray and cable locations on the vehicle.

Another difference in batteries is their power ratings. The most commonly used number is the Cold Cranking Amp (CCA) capacity, which is the maximum number the amps the battery can deliver when cranking the engine. The higher the number, the more amps the battery can provide for reliable cold starting.

Another power rating number that's important but may be less familiar is the battery Reserve Capacity (RC) rating. This is how many amp hours of current the battery can provide should the charging system fail. A replacement battery should have CCA and RC that meet or exceed the OEM battery requirements.

Battery date codes are also important. Batteries age on the shelf, so the oldest ones should always be sold first to keep the stock fresh. The number/letter date code on the battery reveals when it was manufactured. The number indicates the year, and the letter corresponds to the month (A = January, B = February, C = March, etc.)

To prevent comebacks, new and used batteries should be tested to confirm their state of charge and condition. A low battery that still has good cell plates can be recharged and returned to service. But if a battery fails a load test or will no longer accept a charge, it must be replaced. Batteries containing lead and should always be recycled. Handle all batteries with care because they contain acid.

Related items that may be needed include replacement battery cables, clamps, battery tray and mounting hardware.


The alternator is part of the charging system and generates voltage to keep the battery charged and to operate the ignition system, computer and other electrical accessories on the vehicle. The alternator is belt driven and produces an alternating current (AC) that is converted into 12 volts of direct current (DC) by diodes (the rectifier assembly) on the back of the alternator. The output voltage is controlled by the engine computer or an internal or external voltage regulator according to demand. The higher the load on the electrical system and battery, the higher the charging output of the alternator. Most charging systems that are working properly produce a charging voltage of about 13.8 to 14.2 volts at idle with the lights and accessories off.

A defective alternator will not meet the electrical needs of the vehicle and will allow the battery to run down. Alternator output can be tested with a volt meter, ammeter or special test equipment. Noisy shaft bearings may also require alternator replacement.

Alternators often fail because of excessive heat and electrical overloads. The higher electrical loads that are common in many vehicles today can tax many OEM alternators to the limit, especially those that are equipped with high-output aftermarket audio systems, auxiliary lighting and other electrical accessories that increase the amp load on the charging system. One of the most severe applications for alternators is emergency vehicles. The alternators on these vehicle may only last a year or so before they fail and have to be replaced.

Replacement alternators should always have the same or higher amp rating as the original. An upgrade option here would be a high-output alternator designed to handle higher loads and temperatures. Some of these premium-priced units have twice the output of a stock alternator and can greatly extend alternator life in demanding applications. Most are bolt-on replacements for the stock alternator, but heavier gauge cables are also required to handle the higher output.

Starters are replaced less often than alternators because they are only used to start the engine. Fuel-injected engines usually require little cranking to start so the starter doesn't have to work very hard - except during cold weather when the oil in the engine thickens and makes it harder to crank. Prolonged cranking is what kills many starters because heavy cranking causes the starter to overheat.

The starter is mounted on the engine or transmission bellhousing and engages teeth on the flywheel to crank the engine. A one-way overrunning clutch is used to protect most starters against damage should the starter remain engaged after the engine starts.

There are several different types: direct-drive starter motors, gear-reduction starter motors and permanent magnet starter motors (reduced-size starters with permanent-magnets inside instead of wire coils). Handle permanent-magnet starters with care because banging them on the counter or floor may break the magnets inside.

Because of the high-load on the starter, good electrical connections are extremely important. Loose, corroded or undersized battery cables may not deliver enough amperage to crank the engine at normal speed, causing hard starting. Starter drives (which can be replaced separately on many starters) can also fail, preventing the motor from engaging the flywheel. A bad solenoid or relay will prevent the starter motor from cranking at all. Accurate diagnosis of a starter problem is important to prevent unnecessary parts replacements and returns.

Battery cables should be replaced if loose, damaged or too small for the application. Engine ground straps are equally important and are an often-overlooked cause of charging and starting problems.

Fuses protect against electrical overloads and are designed to blow if there's too much current in a circuit. Overloads should not normally occur, so if a fuse has failed, there may be a short in the circuit. Replacement fuses must have the same amp rating as the original. Fuses are located in various places, but most commonly in a box or panel under the dash, or in the engine compartment. Some circuits also have in-line fuses to protect wiring or components (such as aftermarket sound systems and other accessories.)

Relays are switching devices used to route power to other components such as the fuel pump, ABS system, lights and so on. Relays may be located in the engine compartment or almost anywhere in the vehicle (locating a particular relay often requires referring to the vehicle's wiring diagram.)

Lamps and bulbs for interior and exterior illumination come in various sizes and styles. Replacement lamps and bulbs must have the same mounting and electrical connections as the original (compare the old and new bulbs or refer to an application chart), but headlamps can often be upgraded for more light output with higher-output bulbs.


Editors Note: There will be three questions on the P2 test that deal specifically with the emission control system.

One of the main purposes of computerized engine controls is to reduce emissions. Vehicle manufacturers started using computers over 20 years ago to control ignition timing, fuel delivery and other emission functions because electronics were better suited to this purpose than mechanical systems. Over the years, engine control systems have gotten smarter, faster and better at self-diagnosing emission problems.

All 1996 and newer vehicles have Onboard Diagnostics II (OBD II) as part of their programming to detect and identify emission faults. OBD II monitors ignition misfires, the efficiency of the catalytic converter, the operation of the engines sensors and feedback fuel control loop and many other functions. The system is programmed to turn on the Malfunction Indicator Lamp (MIL) - more commonly known as the "Check Engine" lamp - when emission problems are detected.

Many metropolitan areas of the country also require annual or periodic emissions inspections. The simple tailpipe idle test has mostly been replaced with loaded-mode dyno testing that simulates actual driving conditions. More and more emission programs are also including an OBD II check or replacing loaded mode testing with the faster and easier OBD II check. If the lamp is off and no faults are found, the vehicle passes inspection. If a vehicle fails an emissions test, however, further diagnosis is needed to determine which systems are involved and which parts need to be replaced. Thats where fault codes help. This requires the use of a scan tool and other test equipment to isolate the problem. For more information on OBD codes, see the July issue, Check Engine Light - Opportunity or Obstacle.


One way the engine-control system minimizes pollution is by carefully controlling the air/fuel mixture. Balancing the mixture so it is not too rich or too lean allows complete combustion and reduces harmful byproducts. The engine computer does this by monitoring the amount of unburned oxygen (O2) in the exhaust with an oxygen sensor mounted in the exhaust manifold. A voltage signal produced by the O2 sensor tells the computer if the mixture is rich (little O2) or lean (too much O2). The computer then compensates by decreasing or increasing the on time of the injectors to reduce (lean) or increase (richen) the fuel mixture. This is called a "feedback loop" because what happens to the fuel mixture depends on the feedback signal from the O2 sensor.

When a cold engine is first started, the O2 sensor isnt hot enough to produce a signal yet, so the computer supplies a relatively rich mixture while the engine warms up. This is called "open loop" operation because the computer is not receiving or using the feedback signal from the O2 sensor. When the engine reaches a certain temperature and the O2 sensor gets hot enough to produce a voltage signal, it switches to "closed loop" operation and begins to vary the fuel mixture using the O2 sensors feedback signal. A bad coolant sensor can prevent the engine from going into closed loop, causing an increase in emissions and fuel consumption.

Most oxygen sensors generate a voltage signal that switches from about 0.1 volts (lean mixture) to almost 1.0 volts (rich mixture), so the computer can balance the fuel mixture. Some newer wide band O2 sensors generate a higher voltage that is proportional to the amount of oxygen in the exhaust. Most late-model O2 sensors have an internal heater that allows the sensor to reach operating temperature more quickly and maintain its operating temperature when the engine is idling. O2 sensors can be contaminated by internal coolant leaks, using the wrong type of RTV sealant on engine gaskets, by ash from burning oil, or by lead from leaded gasoline. A buildup of deposits on the sensor can make it slow to respond to changes in the fuel mixture. A sluggish or dead sensor will cause an increase in emissions and fuel consumption.

In addition to the Powertrain Control Module (PCM) and key engine sensors (oxygen sensor, coolant sensor, throttle position sensor, manifold absolute pressure sensor, airflow sensor, etc.), various subsystems are used to control specific pollutants. These include the Positive Crankcase Ventilation (PCV) system, the Exhaust Gas Recirculation (EGR) system, the Evaporative Emission Control System (EVAP), the Air Injection Reaction (AIR) system and the catalytic converter.

The PCV system recirculates blowby vapors from the crankcase back into the intake manifold so the vapors can be reburned inside the engine. This prevents the escape of blowby vapors into the atmosphere, and it also helps remove moisture from the crankcase to prolong the life of the oil and prevent the formation of engine-damaging sludge. The PCV valve is usually located in a valve cover and is attached to the intake manifold by a hose. The recommended replacement interval is typically 50,000 miles. Clogging can allow pressure to build up inside the crankcase causing oil leaks.

The EGR system reduces the formation of oxides of nitrogen (NOX) in the engine by reducing peak combustion temperatures when the engine is under load. When the engine is under load, intake vacuum drops. This causes the EGR valve on the intake manifold to open a port between the intake and exhaust manifolds. The engine then sucks in some exhaust that dilutes the air/fuel mixture slightly to reduce combustion temperatures. Older EGR valves are vacuum-operated, but many newer ones are electronic. Loss of EGR due to valve failure or clogging can result in increased emissions and engine-damaging detonation (spark knock or ping). If the EGR valve sticks in the open position, it has the same effect as a large air or vacuum leak causing misfiring and rough idle. The EGR valve is calibrated to the engine application, so a replacement valve must have the same flow characteristics. Some aftermarket replacement EGR valves have various adapters to modify the flow rate.

The EVAP system controls evaporative emissions from the fuel system and fuel tank. Fuel vapors are trapped in a charcoal-filled canister, then vented into the engine through a purge valve to be reburned. A leaky fuel filler cap can allow fuel vapors to escape into the atmosphere. Replacement gas caps must be the same type as the original (caps for some older vehicles may be vented, but newer ones are sealed.) Fuel vapor leaks are monitored by the OBD II system.

The Air Injection Reaction (AIR) system on older vehicles uses an air pump to pump extra oxygen into the exhaust system to reduce pollution. A diverter valve assembly on the air pump controls the flow of air into the exhaust manifold. On some vehicles, air is also routed to the catalytic converter. An anti-backfire valve prevents hot exhaust gasesfrom flowing backwards into the system and damaging the diverter valve or air pump. Problems in this system can cause an increase in emissions.

The catalytic converter is an afterburner in the exhaust system that helps reburn unburned pollutants. It contains catalysts that initiate chemical reactions to reduce unburned hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOX). The catalyst inside the converter can be contaminated by lead (leaded gasoline), silicon (coolant leaks) or phosphorus (oil burning), which reduces its efficiency. On 1996 and newer vehicles with OBD II, a second oxygen sensor is mounted behind the converter to monitor its operation. If converter efficiency drops below a certain level, it will turn on the Check Engine light. Converters can also be damaged by overheating if an engine is misfiring, leaking compression or burning oil. If the converter gets too hot, the ceramic honeycomb inside may melt causing an obstruction in the exhaust. A plugged converter will create backpressure that reduces engine performance and may even cause the engine to stall. There is no way to clean a plugged or contaminated converter, so replacement is the only option. Replacement converters must the be the same as the original.


Editor's Note: There will be three questions on the P2 test that deal specifically with engine mechnical parts.

Engine parts include those in the block (crankshaft, main and rod bearings, connecting rods, pistons and rings, oil pump), valvetrain components (camshaft, lifters or followers, pushrods, valves, springs, retainers, rocker arms, valve guides, seals and seats), plus the cam drive (timing gears, timing chain or timing belt) and assorted gaskets and seals (head gasket, pan and cover gaskets, manifold gaskets, crankshaft front and rear main seals).

Engine parts may be sold individually, in sets or in complete overhaul kits that include most of the parts that are commonly replaced when rebuilding an engine. Identifying the engine application is essential for looking up the correct replacement parts. In addition to the vehicle year, make and model, the engine displacement (in cubic inches (CID) or liters (L), and sometimes the vehicle identification number (VIN) or engine code is needed to accurately identify the motor. Some engines that have the same displacement may have different compression ratios, camshafts, cylinder heads, valves or other parts.

There are two basic types of reciprocating piston engines in production today: pushrod and overhead cam (OHC). Pushrod engines have a single camshaft in the engine block that uses lifters and pushrods to operate the valves. The cam is driven at half the speed of the crankshaft by gears or a gear set and timing chain. Overhead cam engines have one or two camshafts in the cylinder head to operate the valves directly or via followers. The cam(s) are driven off the crankshaft by a timing chain or belt.

In single overhead cam (SOHC) engines, there is one camshaft per cylinder head, and the cam operates both the intake and exhaust valves. In dual overhead cam engines (DOHC) there are two cams per cylinder head. One cam operates the intake valves, and the other cam operates the exhaust valves. Some late-model SOHC and DOHC engines also have variable valve timing (VVT). A mechanism on the end of the camshaft uses oil pressure to advance or retard cam timing as engine rpm and/or load change to improve engine performance and fuel economy.

Another difference in engine design is the configuration of the block. There are in-line three, four, five and six cylinder engines, V-engines (V6, V8, V10 and V12) where each bank of cylinders is usually angled 60 to 90 degrees apart, W-engines (such as Volkswagen's W8 engine) where there are four rows of pistons staggered at different angles, and horizontally opposed engines (Porsche, Subaru and older air-cooled VW) where the opposing cylinder banks are directly opposite one another (180 degrees apart). Engine blocks may be cast iron or aluminum with or without steel cylinder liners or sleeves.

One design that is totally different from all of the others is Mazda's rotary engine (also called a "Wankel" engine after its inventor). A rotary uses a pair of triangular shaped rotors that wobble around inside figure-eight-shaped "epitrochoidal" combustion chambers. The three leading edges of each rotor have "apex seals" that act like piston rings to seal the gases. Each rotor is mated to the crankshaft with an internal gear and bearing arrangement, and no valves are used. The engine sucks air like a two-stroke.


Back to the more conventional engines. Most engine blocks are cast iron, but a growing number are made of aluminum with or without iron cylinder liners. Cylinder heads that hold the valves and upper valve train components may be cast iron or aluminum. The cylinder heads on pushrod engines have two valves per combustion chamber (one intake and one exhaust). Heads on OHC engines may have two, three, four or even five valves per cylinder (one intake and one exhaust, two intakes and one exhaust, two of each or various combinations thereof). Having more valves improves high rpm breathing and power.

The intake valves in the cylinder head open and close to allow air and fuel to enter the combustion chambers. The exhaust valves allow the burnt gases to escape. Exhaust valves run much hotter than intake valves and are more vulnerable to burning and failure. Exhaust valves are often replaced when an engine is given a "valve job" (a process that involves refacing the valves and seats to restore compression.) that are machined into the head and ride up and down in integral guides in the head. But some (such as big-block Chevy) have replaceable press-fit valve guides. Aluminum is too soft for seats and guides, so all aluminum heads have hard alloy valve seat inserts and replaceable press-fit cast iron, powder metal or bronze valve guides. Worn valve guides are a common problem in high-mileage engines and allow the engine to use oil. Excessive oil consumption can foul spark plugs and cause heavy carbon deposits on the intake valves and in combustion chambers. Worn guides can be replaced or repaired by sleeving to restore clearances, or they can be reamed to oversize to accept new valves with oversize stems.

At the top of each valve guide is a seal to control lubrication. "Umbrella" seals act like a shield to deflect oil away from the guides while "positive" seals fit tightly around the stem to control lubrication. Most late-model engines have positive valve guide seals.

Valves are opened by eccentric lobes on the camshaft. In pushrod engines, lifters ride on the cam lobes and transfer the motion of the lobs through pushrods to rocker arms that push the valves open. Some older engines have solid lifters that require periodic valve lash adjustments, but most engines have hydraulic lifters that use oil pressure to main proper valve lash in the valvetrain. Lifters may be "flat-bottom tappets" that ride directly on the cam lobes, or they may be roller lifters that ride on a small roller to reduce friction. In OHC engines, the cam lobes may push directly on the tops of the valve stems or use followers with or without hydraulic lash adjusters to open the valves.

Valves are closed by stiff springs mounted around the valve stems. A groove in the top of each valve stem accepts keepers that hold the spring retainer in place. Shims called valve spring inserts may be used under the springs to increase spring tension. Valve springs weaken with age, causing a loss in compression. Springs can also break. Weak or broken springs must be replaced. New springs are recommended for high-mileage engines and new camshafts.

Camshafts may need to be replaced if the lobes have become worn. Replacement cams may be new or reground with stock lobe profiles or performance profiles. Increasing valve lift with taller lobes and valve duration (open time) can add more horsepower. New lifters should be installed if the camshaft is replaced. Aftermarket performance cam kits usually include new lifters and valve springs.

Camshaft timing gears wear with age, and timing chains stretch. This can reduce engine performance and cause noise. Rubber timing belts maintain cam timing more accurately over the long haul, but must be replaced at 60,000- to 100,000-mile intervals to reduce the risk of breaking. A broken timing belt may bend valves in an interference engine that lacks enough valve-to-piston clearance.


Problems in the engine block include worn cylinder bores, worn or damaged pistons and rings, and worn bearings. Worn or damaged cylinder bores can sometimes be restored by boring and honing to oversize, or by sleeving. Worn cylinders increase oil consumption and blowby.

Pistons are the reciprocating components inside the cylinders that compress the air/fuel mixture and transmit the force of combustion to through rods to the crankshaft. Pistons may be cast aluminum, a special high-strength "hypereutectic" aluminum alloy or aluminum forgings. The latter two are used in high-output and performance applications. Some pistons have a moly coating on the "skirt" (side) to reduce scuffing and wear. Pistons that are cracked, burned or worn must be replaced. Replacement pistons should be the same type or better than the original for durability.

Three rings are used to seal the pistons with the cylinders, a top compression ring, a middle compression ring and a lower oil ring (usually a three-piece design). Worn or broken rings reduce compression, increase blowby into the crankcase (which contaminates the oil) and increase oil consumption. Oversized pistons and rings are required if the cylinders are bored and honed to oversize. Rings are made from various materials and may have different facings. Cast iron rings are used in most passenger car engines. But higher output engines, diesels, turbocharged and supercharged engines as well as some late-model engines have steel or ductile iron top compression rings. Rings may be "plain faced" (no coating), "moly faced" (most common), chrome plated or "nitrited" (many Japanese rings). Most late-model rings are thin low-tension-style rings that reduce friction. Replacement rings must be the same size and thickness as the original and should also be the same or better material as the original for durability.

The pistons are joined to the crankshaft by connecting rods. A wrist pin mates the small end of the rod to the piston. The large end of the rod has a removable cap that bolts around the crankshaft journal. Connecting rods are usually cast iron. New rods are needed if the old ones are cracked, twisted, bent or stretched. For performance applications, forged steel, aluminum and titanium rods are available.

Bearings support the crankshaft (and camshaft in pushrod engines). A thin film of oil between the bearings and shafts reduce friction and prevent wear. Bearings may be aluminum or steel with an aluminum or tri-metal (copper/lead/babbitt) overlay. Worn bearings produce noise and lower oil pressure. Bearing failure can occur if a bearing overheats and seizes, cracks or pounds out. Bearings can be damaged by dirt, lack of lubrication or oil breakdown. Wear can be accelerated by neglecting regular oil and filter changes. Bearings are usually replaced as complete sets, and must be the correct size for the crankshaft journals. If the crankshaft has been reground to undersize, undersize bearings are required to maintain proper oil clearances.

All engines have an oil pump to circulate oil from the oil pan to the bearings and the rest of the engine. A spring-loaded valve controls the amount of oil pressure generated by the pump. The pump is driven off the crankshaft and may be located in the crankcase or under the front cover. A worn oil pump can lower oil pressure. Recommend a new oil pump if the bearings are being replaced or the engine is being overhauled. The oil pickup tube and screen should also be replaced.


Engines contain a variety of gaskets to seal fluids and gases. Head gaskets seal the cylinder head and block. Head gaskets may have nonasbestos or graphite facings on a solid or perforated steel core, or they may be made of multi-layer steel (MLS). A leaky head gasket can allow coolant to enter the combustion chamber and/or a loss of compression. Head gasket failure can be caused by overheating or improper installation. Replacing a head gasket may require resurfacing the cylinder head and/or block.

Valve cover and oil pan gaskets may be cork or molded silicone rubber. Other gaskets that may be needed when doing engine work include the timing cover, manifold and thermostat gaskets as well as crankshaft and valve seals.


All engines require oil as well as regular oil and filer changes. Most late-model engines are factory filled with 5W-30 multi-viscosity oil. 10W-30 oil is the most popular viscosity for older or higher mileage engines, but use the viscosity recommended by the vehicle manufacturer. Thinner oils work well in colder climates and thicker oils work well in hotter, hard-use environments.

Motor mounts hold the engine in place and dampen vibrations, and they should be replaced if collapsed or broken.


Editor's Note: There will be two questions on the P2 test that deal specifically with the exhaust system.

The exhaust system begins at the exhaust manifold and goes all the way to the tailpipe.

The exhaust manifold is bolted to the cylinder head and routes hot exhaust gases into the rest of the exhaust system. The manifold may be cast iron or welded stainless steel tubing. Manifolds run extremely hot and occasionally crack allowing exhaust gases and noise to leak into the engine compartment. Aftermarket replacement exhaust manifolds are available for many engines. Related items that should also be replaced if changing a manifold include the exhaust manifold gasket and the manifold mounting bolts.

The next item down the line is the "head pipe." Usually made of stainless steel, the head pipe connects the exhaust manifold to the catalytic converter. Some engines don't have a head pipe. The converter attaches directly to the manifold. On V6 and V8 engines with a single exhaust system, the head pipe is called a "Y-pipe" because it is shaped like a Y and joins the two sides together into a single outlet. On some import front-wheel drive cars with transverse-mounted engines, the head pipe has a ribbed flexible section covered by stainless steel webbing. This allows the pipe to flex as the engine rocks. After many miles, the flex section eventually cracks and starts to leak. Flexible head pipes are very expensive to replace, so there are flexible repair sections that can be welded into an existing pipe (this requires professional installation).

Behind the head pipe is the catalytic converter (see the section on emission controls for additional details). There are four basic types: "Two-way" converters in pre-1980 vehicles that reduce unburned hydrocarbons (HC) and carbon monoxide (CO), "Three-way converters" (TWC) in many 1980 and newer vehicles that reduce HC, CO and oxides of nitrogen (NOX), "Three-way plus oxygen" converters in newer vehicles that have additional plumbing to accept air from an air pump to reduce HC, CO and NOX, and "OBD II" converters that are essentially three-way converters certified to meet OBD II requirements.

Since 1995, new converters have been covered by an 8-year/80,000-mile federal emissions warranty. Converters can be contaminated by oil burning and internal coolant leaks in the engine, and damaged by overheating (often from ignition misfiring). If the converter is plugged or has failed an emissions test, the replacement converter must be the same type as the original. Aftermarket converters are less expensive than OEM converters, and are now available for 1996 and newer vehicles with OBD II.

Behind the converter is usually another pipe that connects to a muffler or resonator. Mufflers contain tubes and baffles to reduce exhaust noise. Most OE mufflers are of a three-tube design to provide maximum sound control. Resonators contain fewer tubes and baffles and are used primarily to "tune" the sound of the exhaust. Some vehicles use both, others use just a muffler.

Mufflers and resonators usually fail from the inside out. Exhaust contains corrosive acids and moisture. When the engine is shut off, moisture condenses and puddles in the muffler. Over time, the resulting corrosion can eat through the shell. Most late-model vehicles now have mufflers made of long-lasting stainless steel, but most aftermarket replacement mufflers are aluminized steel or coated steel.

Replacement mufflers are available in various price ranges. The best (and most expensive) are premium mufflers that provide superior sound control and corrosion resistance. These may have extra tubes and baffles, fiberglass "roving" for additional sound absorption and a lifetime warranty. Next would be a standard replacement muffler, which is often a direct bolt-on replacement. There are also universal mufflers that can be installed on a wide variety of applications using pipe adapters, and low-cost economy mufflers for those who are mostly concerned with keeping their repair costs down.

Polished stainless steel performance mufflers and resonators are also available for many vehicles and are especially popular on sports compact cars. Many have straight-through designs to reduce backpressure for more horsepower. "Turbo"-style performance mufflers and other low-restriction designs are also popular upgrades for customers who want to uncork the exhaust.

Chrome and stainless steel exhaust tips are also popular. And the bigger the better. These bolt-on exhaust accessories are affordable and easy to install. They don't really do much for performance, but they look cool and that's what many young drivers want.

Exhaust work often requires special tools too. These include pipe cutters and pipe chisels for separating corroded pipes and connectors, and expanders for repairing or installing new pipes and mufflers.

Other parts an exhaust customer may need include clamps (a must when replacing most pipes and mufflers), hangars and fasteners.


Editor's Note: There will be three questions on the P2 test that deal specifically with the HVAC system.

The major components in the heating and A/C system are the A/C compressor, orifice tube or expansion valve, condenser, evaporator, accumulator or receiver/drier and heater core.

The A/C compressor is the heart of the refrigeration circuit. It pumps and pressurizes the refrigerant. The compressor is belt driven by the engine, and most have a magnetic clutch that cycles the compressor on and off. Some compressors have four pistons that may be positioned radially (outward) to the compressor's crankshaft (GM R4 compressors), or five or six pistons that are parallel (axial) to the shaft (such as Harrison H6 compressors). Some are variable displacement compressors that pump more or less refrigerant as the cooling demands on the system change. Other compressors have no pistons and use vanes or a scroll design to pump refrigerant.

Compressor failures are often caused by loss of lubrication, which in turn may be due to a blockage in the orifice tube or expansion valve. Most compressors do not hold much oil and rely on oil circulating with the refrigerant for lubrication. If the A/C system has a leak and loses refrigerant, it will also lose oil. Anyone who is replacing a compressor, therefore, should be advised to add oil too.

Different types of compressors require specific types of oil. Older R12 A/C systems require mineral oil, while newer R134a systems use mostly PAG oil. Older R12 systems that have been retrofitted to R12 can use POE oil or PAG oil. Follow the compressor manufacturer's recommendations for the type and viscosity of lubricant to use. Using the wrong lubricant can cause compressor failure.

Replacement compressors may contain the proper lubricant for the vehicle application, but some may contain a temporary shipping oil that must be drained out prior to installation. Others are shipped dry. Anyone who is replacing a compressor may also need a new drive belt.

Refrigerant from the compressor goes to the condenser, which is a heat exchanger mounted in front of or next to the radiator. Here, it cools, changes into a liquid and flows to the orifice tube or expansion valve, which are flow-metering devices (an A/C system will have one or the other but not both.) Orifice tubes are located in the high-pressure liquid line between the condenser and evaporator.

When refrigerant passes this point in the system and enters the evaporator, it changes back into a vapor. This has a chilling effect that cools air flowing past the evaporator.

Condensers and evaporators are both vulnerable to internal corrosion and blockages (usually as a result of moisture contamination in the system). Condensers can also be damaged by stones and other road hazards that pass through the grille, and they can trap debris internally that comes from a compressor failure. If this debris is not removed, it will likely cause the replacement compressor to fail too. Serpentine-style condensers can often be flushed successfully with approved flushing chemicals or liquid refrigerant, but condensers with parallel tubes or extremely small passageways are difficult to flush and should be replaced. An in-line filter should also be installed in the system for added protection following a compressor failure.

The accumulator or receiver/drier is a device that serves as a refrigerant reservoir and a system filter. It contains a bag of moisture-absorbing crystals called desiccant. Moisture in an A/C system can cause acids and sludge. A new accumulator or receiver/drier should be installed if the compressor, condenser or evaporator are being replaced or if the system has been open and exposed to air for more than a day.

A new orifice tube should also be installed following a compressor failure, or if the system is contaminated with sludge. Aftermarket variable displacement orifice tubes can improve low-speed cooling on older vehicles that have been retrofitted to R134a. Some newer vehicles have variable orifice tubes from the factory.

Other parts that may need to be replaced include hoses, O-rings and seals. The suction hose is located between the evaporator and the condenser. The high-pressure hose is located between compressor and condenser. Newer vehicles with R134a A/C systems all require nylon-lined barrier-style hoses with preformed end fittings. Older vehicles that are being retrofitted to R134a usually don't need new hoses (unless one is leaking), but some of the O-rings may have to be replaced with ones that are R134a-compatible.

Many A/C systems have a low-pressure cutout switch to protect the compressor should a leak allow the refrigerant to be lost. When pressure drops below a certain point, the switch prevents the compressor clutch from engaging. Many systems also have a high-pressure cutout switch that turns the compressor off if the pressure gets too high, which can occur during extremely high load, high-temperature conditions.

A/C systems require one of two types of refrigerant: R12 (Freon) for most 1993 and older vehicles, or R134a for most 1994 and newer vehicles. The two different refrigerants should not be intermixed. Most older R12 systems can be converted to R134a with minimal changes, but some Ford and Japanese cars do not have compressors that can handle R134a. Only certified professionals can purchase R12 legally. Other alternative refrigerants are available for older R12 applications, but vehicle manufacturers recommend retrofitting to R134a if R12 is unavailable or too expensive.

The heater is not part of the refrigeration system and uses engine coolant to provide warmth to the passenger compartment. Hot water from the engine circulates through the heater core, which is connected to the engine and water pump with hoses. Heater output depends on engine temperature (which requires a good thermostat and a full coolant level) and air routing through the heating ventilation and A/C (HVAC) system. Blend air control doors direct incoming air through the heater (for heating), A/C evaporator (for cooling) or both (in defrost mode to dehumidify the air so the windows don't steam over.)

Other parts that affect the operation of the A/C and heating system include the heater blower motor, heater control valve (restricts coolant flow to the heater core), radiator/condenser cooling fan(s) and the automatic temperature control system.

One other item that may need to be replaced on newer vehicles is the cabin air filter. Located behind the glove box or at the base of the windshield, the filter stops dust, pollen and odors from entering the passenger compartment. A plugged filter can restrict airflow and reduce ventilation, heating and cooling. This filter should be replaced yearly.


Editor's Note: There will be three questions on the P2 test that deal specifically with fuel systems.

Electronic fuel injection systems come in several versions. Throttle-body injection (TBI) was used in the 1980s on many vehicles as an intermediate step from electronic carburetion to multiport fuel injection. TBI uses one or two fuel injectors mounted in a throttle body to fuel the engine. Multiport fuel injection (MFI) systems, which are used on almost all late-model engines, have a separate fuel injectors for each cylinder. First generation MFI systems fired all the injectors simultaneously or each bank separately, but most of the newer MFI systems are sequential fuel injection (SFI) systems that fire each injector separately just as the intake valve is about to open.

Another variation is General Motor's "central point injection" (CPI) system. Here, a centrally-located "Maxi" injector routes fuel to mechanical poppet valve injectors at each cylinder. When fuel pressure in the line exceeds a certain value (37 to 43 psi), the spring-loaded ball valve opens, and fuel sprays out of the injectors. The CPI system works much like an old Bosch K-Jetronic fuel injection system except that the electronic Maxi injector replaces the complicated mechanical K-Jetronic fuel distributor.


The fuel injectors are the business end of the fuel delivery system. The injectors spray fuel into the intake ports. The fuel vapor is mixed with air and drawn into the cylinders. Most injectors are electronic and have a solenoid valve at the top to open the nozzle. When the solenoid is grounded or energized, the valve is pulled open allowing fuel to spray out of the injector. The powertrain control module (PCM) determines the on time of each injector pulse to regulate fuel delivery (a longer "on" time means more fuel and a richer mixture.) The PCM uses inputs from the oxygen sensor in the exhaust as well as throttle position, engine speed, load and airflow to control the injectors.

Dirty injectors are a common problem. Injector nozzles can become clogged with fuel varnish over time, causing a loss of engine performance and misfiring. Injectors can also leak fuel, causing an increase in fuel consumption and emissions. An injector failure will result in a dead cylinder and power loss. A shorted injector may rob voltage from the other injectors and cause the engine to stall. Dirty injectors can often be cleaned to restore performance. Fuel cleaning additives help, but the best results are obtained with on-car flushing or off-car cleaning. New injectors are expensive, so instead one can opt for aftermarket remanufactured injectors.

Fuel pressure for the fuel-injection system is created by an electric pump usually located inside the fuel tank. The pump is energized by the PCM through a relay when the engine is cranked and started. Pressure ratings vary depending on the application, but typically it ranges from 35 to 85 psi. Pump designs also vary and include single or double-vane, roller vane, turbine or gerotor-style pumps. Most have a one-way check valve to maintain pressure in the fuel system when the engine is shut off (for easier starting the next time.)

Fuel pumps can fail for a variety of reasons: old age, loss of voltage or ground at the power relay, wiring connections or pump motor, or bearing damage. Running the fuel tank empty may damage the pump because it relies on fuel for lubrication. Accurate diagnosis is essential to prevent unnecessary pump replacements and returns.

Replacement fuel pumps must have the same pressure rating and flow characteristics of the original. The pump is usually part of the fuel sending unit and may be replaced separately or as a complete assembly. The fuel inlet strainer sock should also be replaced when the pump is changed.

The fuel tank must be dropped to replace the pump, and the inside should be inspected for dirt or rust that could cause the new pump to fail. A tank that is badly corroded inside or is leaking must be replaced.

An inline fuel filter between the fuel pump and engine protects the injectors from dirt, sediment or rust that gets sucked through the pump. Most newer vehicles do not have a specified replacement interval for changing the fuel filter, but replacing it every two to three years for preventive maintenance is still a good idea.

When fuel reaches the engine, it enters a fuel rail and goes to the injectors. A fuel-pressure regulator on the fuel rail maintains a certain operating pressure. Inside is a spring-loaded diaphragm attached to a source of intake vacuum. As engine load (vacuum) changes, pressure is adjusted up or down as needed to maintain proper fuel delivery. Excess fuel is routed back to the fuel tank through a return line. Some newer vehicles have returnless systems with the regulator mounted in the fuel tank with the pump. Regular problems can affect engine performance.

Airflow into the engine is regulated by a throttle body attached to the intake manifold. Air first flows through an air filter, then the throttle body before passing through the manifold and into the engine. The PCM must monitor the amount of air entering the engine so some fuel-injected systems have a vane or mass airflow sensor ahead of the throttle body. Other systems estimate airflow based on throttle position, rpm, temperature and engine load.


Carburetors haven't been used since the early 1980s, but there are still some older classic cars and trucks that may need fuel-related replacement parts. These include carburetor rebuild kits, chokes, gaskets, fuel pumps and fuel hose.

Rebuild kits include many of the commonly-replaced internal parts such as gaskets, seals, accelerator-pump diaphragms and needle valve. A hollow brass or nylon float in the fuel bowl to controls how much fuel enters the carburetor. These are not included in kits but are available separately.

The choke is a flap atop the carburetor that restricts airflow into the carburetor. The choke is used to make cold starting easier, and it is usually controlled by a temperature-sensitive spring inside the automatic choke housing. Problems here can make an engine hard to start.

Many carburetor problems car caused by an accumulation of fuel varnish deposits that restrict or block metering circuits and jets. Aerosol carburetor cleaner can often wash away most of these deposits. Fuel system additives help too.

Carburetors don't require much fuel pressure, so a low-pressure (four to eight psi) mechanical pump or electric pump is used to deliver fuel to the engine. Mechanical pumps are mounted on the engine and driven off of the camshaft. If the diaphragm or check valves inside the pump leak or fail, the pump needs to be replaced.


Editor's Note: There will be three questions on the P2 test that deal specifically with the ignition system.

All gasoline-fueled engines have a spark-ignition system to ignite the air/fuel mixture in the cylinders. The spark is created by a high-voltage surge from an ignition coil. The coil is triggered by an ignition module and/or the PCM using a signal from a distributor pickup or crankshaft position sensor. High voltage from the coil travels though a thickly insulated cable to the spark plug where it jumps across the plug's electrodes creating a spark.

If the engine has a distributor, a single coil is used on most engines to supply high voltage to all the spark plugs (a few Japanese applications use two coils). If the engine has a distributorless ignition system (DIS), each spark plug has its own separate coil. On General Motors waste spark DIS systems, two spark plugs share the same coil. Many newer vehicles have coils that are mounted directly over the spark plug and use no plug wires. These are called coil-on-plug (COP) ignition systems.

The most commonly replaced ignition parts are the spark plugs and plug wires. On older vehicles with distributors, the distributor cap and rotor are also service items. Ignition coils, modules and sensors are only replaced if they have failed.

Ignition coils come in various shapes and sizes, but all do essentially the same thing: they are step-up transformers that convert 12 volts DC into 7,000 to 40,000 or more volts DC. The actual voltage required to fire a spark plug will vary depending on engine speed, load, temperature, resistance in the plug and wires, and the distance across the spark plug electrodes.

Inside the coil are two sets of copper wire windings, one inside the other. The primary windings are made up of several hundred loops of heavy wire around the iron core of the coil. The secondary windings consist of several thousand turns of very fine wire inside the primary windings. When the primary current is switched on, the coil charges up and creates a powerful magnetic field. When the primary current is switched off, the collapse of the magnetic field induces a high-voltage surge in the secondary windings that creates the spark.

If the coil windings short out or break, the coil may not produce enough voltage to fire the spark plugs causing the engine to run rough or die. Hairline cracks in the coil housing or insulation can also weaken or kill the spark. Coils can be tested by measuring their primary and secondary resistance with an ohmmeter and/or a spark tester. Replacement coils must be the same type as the original to match the engine's voltage requirements.

Electronic ignition systems all use some type of transistorized switching module to turn the coil(s) on and off. On some vehicles (GM and Ford), the module may be mounted on or in the distributor. On DIS systems, it is often part of the coil pack assembly. Modules can be damaged by heat and vibration. A module failure will usually cause a no-spark, no-start condition. GM high-energy ignition (HEI) modules in older vehicles require a thin layer of dielectric grease underneath to conduct heat away from the module. Forget the grease and the module may not live long.

Ignition modules may receive a trigger signal directly from a distributor pickup (magnetic, Hall effect or optical), a crankshaft position sensor or the PCM. A fault in any of these other components or the wiring can prevent the ignition system from firing. Accurate diagnosis is essential to prevent unnecessary parts replacements and returns.

If a vehicle has a distributor, the cap and rotor may develop carbon tracks and cracks over time. This can lead to ignition misfire and hard starting. Replacing the cap and rotor when the spark plugs are changed is often necessary to restore like-new ignition performance.

On older vehicles, the distributor may contain spring-loaded weights that control spark advance as engine speed increases, and/or a vacuum advance diaphragm that retards spark advance when the engine is under load to reduce the risk of detonation (spark knock). The distributor is usually driven off the camshaft, so wear in the timing gears, timing chain, timing belt or distributor drive gears can upset ignition timing. A replacement distributor is needed if the drive gears or shaft bushings are worn.

Plug wires connect the distributor or individual coils to the spark plugs. Also called ignition cables, they come in various types (suppression and solid core - also called mag wires) and with various types and grades of insulation and jacketing (silicone, EPDM and other materials). The higher the temperature resistance of the insulation and jacketing, the better. Cable diameters are usually seven or eight milimeters, and each cable is a different length to fit specific spark plugs. Replacement cables must be the same size and length as the original. Plug wires may be replaced individually or in complete sets (wires should be changed one at a time to avoid mixing up the firing order.) Replacement is needed if internal resistance in the wires exceeds specifications, the wiring is damaged (cracked or burned insulation, or visible arcing or misfiring when the engine is running), or the plug boots or terminals fit poorly or are loose.

Finally, we come to the business end of the ignition system, the spark plugs. Spark plugs come in different sizes, lengths, threads and electrode configurations, but all have some type of center electrode surrounded by a ceramic insulator in a threaded steel shell.

The heat range (operating temperature) of a spark plug depends on the length and shape of the ceramic insulator. The spark plug has to run hot enough so that fuel deposits don't build up on the tip, foul the electrode and cause it to misfire. But it also has to conduct enough heat away from the tip so the tip doesn't get too hot when the engine is under load and cause preignition. Many spark plugs have a copper core center electrode that improves heat conduction and gives the plug a broader operating range.

Spark plugs are designed for specific engines. The diameter, length and pitch of the threads that screw into the cylinder head must match the application. How far the tip of the spark plug extends into the combustion chamber (called "reach") must also be correct for the application, otherwise the tip of the plug may hit the piston or valves. Always follow the spark plug listings in your plug supplier's catalog or data base.

The distance across the electrode gap at the end of most spark plugs must also be set to certain specifications for the engine to run properly. If the gap is too narrow, the spark may not be long enough to ignite the fuel mixture reliably resulting in ignition misfire. If the gap is too wide, there may not be enough available voltage to create a spark also causing ignition misfire. Most spark plugs are pregapped at the factory, but the gap should always be checked and readjusted if necessary when new spark plugs are installed. The exceptions here are Bosch Plus4 and Plus2 spark plugs which have a unique electrode design and should not be readjusted. The gap on ordinary spark plugs can be checked with a feeler gauge or plug-gapping tool.

Every time the spark plugs fire, the electrodes wear a little bit. As the miles add up, the gap gets wider increasing the voltage needed to create a spark. Most conventional spark plugs have a recommended replacement interval of 45,000 miles. To extend plug life, platinum and other exotic metals are used to improve the wear resistance of the electrodes. Platinum plugs cost more than regular plugs, but typically last up to 100,000 miles.

To improve ignition performance, some manufacturers offer spark plugs with special electrode configurations that expose more spark to the air/fuel mixture. Performance plugs reduce misfires and improve fuel economy and power, and they are a good upgrade for customers who need the best ignition performance.


Editor's Note: There will be two questions on the P2 test that deal specifically with manual transmission and transaxle.

Manual gearboxes are limited mostly to sports and performance cars and include four-, five- and six-speed transmissions. Gearboxes are relatively trouble-free and long-lived provided they are not severely abused. The clutch, however, is a wear component. With every shift, the clutch must be disengaged and engaged. Stop-and-go driving in heavy traffic is especially hard on a clutch because the driver is always riding the clutch pedal. After millions of such cycles, the clutch eventually wears out. It may start to slip, chatter or make noise.

Other clutch problems that may appear include oil contamination from engine or transmission oil leakage, disengagement problems brought on by a faulty hydraulic linkage, clutch cable or fork, or noise from a bad release bearing or pilot bearing or bushing (used to support the end of the transmission input shaft in the flywheel.)

Parts that wear out and may have to be replaced in the clutch system include the pressure plate, friction disc, release bearing, pilot bearing or bushing (if used) and components in the clutch linkage (the cable, cable adjuster or in a hydraulic linkage, the master or slave cylinder).

The clutch is bolted to the flywheel on the back of the engine. The pressure plate exerts pressure against the clutch disc to hold it firmly against the flywheel when the clutch is engaged. This allows engine torque to pass directly to the transmission and drivetrain. When the clutch pedal is depressed to disengage the clutch, the pressure plate pulls away from the flywheel. This releases the clutch disc and allows it to slip. This decouples the engine from the transmission so the engine can idle while the vehicle is stopped. Disengaging the clutch is also necessary when shifting gears so the synchos on the transmission gears can help the gears engage smoothly.

Most clutches have a diaphragm spring but some older vehicles have coil spring clutches with nine to 12 coil springs. Diaphragm clutches are used on most newer vehicles because they require less pedal pressure to release than coil spring clutches, are less complicated, last longer and actually increase the clamp load on the clutch disc as it wears (up to a point.)

The clutch disc has friction linings on both sides that grab the flywheel and pressure plate. The disc is mounted on the transmission input shaft with a splined hub which often has five to eight springs to help cushion clutch engagement. Engaging the clutch creates friction, which generates heat. Consequently, the clutch linings can get very hot. The flywheel and pressure plate both act as heat sinks to help carry heat away from the clutch and cool it. But if the clutch gets too hot from excessive slippage or loading, the linings may burn and damage the clutch.

The release bearing that pushes against the diaphragm spring in the clutch, or the release fingers on a coil-spring-style clutch, has ball bearings to reduce friction. If the release bearing wears out, it can make noise when the clutch pedal is depressed. It can also damage the clutch spring or release fingers if it binds up.

On most clutches, the release bearing is held in a yoke or fork that pivots on a ball stud when the clutch linkage moves. On some vehicles, a telescoping hydraulic release bearing is used inside the bellhousing to operate the clutch. Wear or damage to any of these components can also affect the operation of the clutch.

Older vehicles mostly use a mechanical linkage or a cable connected to the clutch pedal to operate the clutch. But most newer vehicles have a hydraulic clutch linkage. A master cylinder attached to the clutch pedal generates hydraulic pressure that moves a slave cylinder attached to the release fork on the transmission bellhousing. With both types of linkages, there are usually return springs and some type of linkage adjustment for the clutch. Accurate adjustment is essential for proper pedal travel and clutch operation.

Replacing a clutch is a major job because of its buried location between the engine and transmission or transaxle. The labor required to do this job can be four to six hours or more on most vehicles. Because of this, most experts recommend replacing all of the major clutch-system components at the same time. Installing a complete clutch kit that includes the clutch pressure plate, disc, release bearing and pilot bearing or bushing will restore the clutch system to like-new condition, reduce the risk of a comeback and save the motorist money by eliminating the need for additional clutch work in the near future. Clutch kits also eliminate the risk of mismatched parts, which can sometimes happen when different clutch components are sourced from different suppliers.

Another item that needs attention when the clutch is replaced is the flywheel. The surface of the flywheel must be clean, smooth and flat. After years of use, it is often scored, grooved and out-of-flat. If runout exceeds specifications and/or the surface is worn, the flywheel must be resurfaced. Some clutch suppliers will not honor a clutch warranty if the flywheel was not resurfaced when the clutch was installed.

Some engines have a dual-mass flywheel which is like two flywheels in one. A dual-mass flywheel helps dampen engine vibrations and cushions clutch engagement for smoother operation. If a dual-mass flywheel is cracked, damaged or the internal springs have failed, it needs to be replaced. Some dual-mass flywheels (Ford) can be resurfaced, but others (GM, BMW and Porsche) should only be replaced. Dual-mass flywheels are very expensive. One alternative is to replace them with a conventional one-piece aftermarket flywheel. These are available for Ford and GM, but they require a different clutch set than the OEM dual-mass flywheel.

Installing a new clutch requires a pilot tool to center and align the disc with the transmission input shaft. Other items that may also be needed include new motor or transmission mounts, engine or transmission seals (if oil leakage caused the old clutch to fail) and gear oil or ATF if it's low.

Though stock replacement clutches are adequate for most vehicles, a stronger clutch may be needed for towing or performance applications. A larger diameter clutch, a clutch with increases spring pressure and/or more durable facings can increase the torque-handling capacity of the clutch as well as durability and longevity.


Editor's Note: There will be three questions on the P2 test that deal specifically with suspension and steering.

The steering system gives the driver control over the vehicle's direction, while the suspension allows the tires to roll over bumps and dips in the road without losing their grip or jarring the driver's teeth loose. Except for periodic checks of the power steering fluid level, the steering and suspension systems on most vehicles today do not require any maintenance. Parts are not replaced until they wear out or are damaged - unless the vehicle's owner is upgrading the suspension for a specific purpose such as increased load-carrying capacity, towing or handling.

The major components in the steering system include the steering box or rack, inner and outer tie rod ends, idler arms, center links, power steering pump and hoses.

Most vehicles today have rack and pinion steering that uses a pinion gear on the end of the steering input shaft to move a horizontal bar (rack) sideways. The rack is connected to the tie rods with sockets, which are enclosed in rubber bellows. The linkage has outer tie rod ends only. On some GM applications, a center-mount rack is used where the tie rods bolt to the center of the rack rather than the ends. Worn inner sockets can cause steering looseness and tire wear. Wear in a power rack control valve housing can increase steering effort. Fluid inside the bellows indicates leaky seals and a need to replace the rack.

The other type of steering system is the recirculating ball steering gear in which ball bearings turn against the worn gear to move the steering linkage. The steering box is connected to the steering linkage with a pitman arm. An idler arm supports the other side of the linkage, which includes a center link, inner and outer tie rod ends and tie rods. Steering wander and looseness can result if the idler arm bushing is worn.

Most vehicles have power steering and use a belt-driven pump to reduce the effort required to steer the wheels. Some power steering pumps also provide hydraulic assist for power brakes (called Hydroboost systems.) A worn pump will usually make noise and/or leak fluid. If a replacement pump does not come with a pulley, the pulley off of the old pump will have to be removed and installed on the new pump. Changing the power steering fluid is also recommended (use the type specified by the vehicle manufacturer.)

Power steering systems have two hoses, a high-pressure hose to carry pressure from the pump to the steering gear or power cylinder and a return hose back to the pump reservoir. Leaks can cause steering problems. Replacement hoses may be preformed or made up using various end fittings and a crimping press.


There are two basic types of front suspensions: short-long arm (SLA) and strut. An SLA suspension uses upper and lower control arms of unequal length to support the steering knuckle. Each arm is connected to the knuckle by a ball joint (one upper and one lower.) A strut suspension typically uses a MacPherson strut in place of the upper control arm and ball joint. The strut combines a shock absorber and spring into one assembly, and serves as the steering pivot for the knuckle. A bearing plate at the top of the strut supports the weight of the vehicle.

On some vehicles, a modified strut configuration is used where the spring is not around the strut but is located between the lower control arm and subframe. On wishbone strut suspensions, the strut supports the weight, but an upper control arm is also used to locate the steering knuckle. Almost all front-wheel-drive vehicles, as well as many rear-wheel-drive vehicles, have strut suspensions. SLA suspensions are used on most rear-wheel-drive cars and light trucks.

Suspension parts that may need to be replaced include ball joints, shocks, struts, control arm bushings and springs. Most people don't think springs ever wear out, but over time the constant force of gravity can cause springs to weaken and sag. This changes ride height and alignment, which can increase tire wear and cause handling and ride problems.

Shocks and struts are the most commonly replaced items because they suffer the most wear. Inside is a piston that pumps back and forth through an oil-filled tube. This creates friction that dampens the motions of the suspension and keeps the vehicle stable and the tires in contact with the road. Control valves in the piston and the bottom of the shock or strut vary the resistance by venting fluid as the velocity of the piston changes. The piston rod has a seal that keeps the oil inside and prevents outside contaminants from entering the shock or strut. But over time, this seal wears out and allows the precious fluid inside to leak out. The shock or strut loses its ability to control the suspension, ride quality goes out the window and the suspension becomes bouncy and rough.

There are two basics types of shocks and struts: twin-tube and monotube. Twin-tube shocks have an oil reservoir around the outside of the piston chamber. Oil moves back and forth from the chamber through the valves in the end of the shock. Monotube shocks are only a single tube with no outer chamber. One end of the shock is filled with pressurized gas with a floating piston seal separating the gas charge from the oil. Twin-tube shocks may also be pressurized with nitrogen gas because gas-charging reduces cavitation, foaming and shock fade. Monotube shocks are typically charged at a much higher pressure (up to 360 psi) and are used more on performance applications because of their quick-acting and firmer ride characteristics.

Shocks and struts are usually replaced in pairs or sets. Replacement shocks and struts with larger piston bores, increased gas pressure or other special features like adjustable valving can be installed to upgrade ride control performance. Likewise, monotube shocks are often used to replace twin-tube shocks to increase suspension stiffness and cornering agility.

One item that may also need to be replaced when replacing struts are the bearing plates atop the strut that allow the strut housing to pivot when the wheels are steered. Looseness in the bearing plate can cause steering noise. Binding may increase steering effort and prevent the wheels from recentering following a turn.

MacPherson strut assemblies require a spring compressor to disassemble and reassemble. Realigning the wheels may also be necessary.

Ball joints are another part that may need to be replaced at some point in the vehicle's life. The joints connect the steering knuckle to the control arms. They may also be used on rear control arms. Joints that carry weight are called loaded joints, while those that do not are called follower joints. SLA suspensions have two upper and two lower ball joints. MacPherson strut suspensions have only two lower ball joints.

A ball joint is so named because of its ball-and-socket construction. The ball stud may ride against a metal gusher bearing, or it may be highly polished to reduce friction and be enclosed in a polymer bearing. Most low-friction ball joints are sealed and do not have a grease fitting for lubrication. Older, gusher-style joints have grease fittings so they can be lubricated periodically.

When ball joints become worn, they can make suspension noise and upset wheel alignment. There is also a danger the joint may separate allowing the suspension to collapse. Replacing a ball joint requires a separator tool or fork to separate the stud from the knuckle once the stud nut has been removed. Some joints are bolted or riveted to the control arm, others are screwed in and others are press-fit into the arm.

Don't forget: the dates for the Fall testing are November 13, 18 and 20!

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