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12th Annual Tech Forum


8/1/2004

 
Your customers have the questions, and youre the ones they look to for the answers. This month, Counterman presents some of the issues surrounding many important
product categories.

Air Conditioning

Q. Is the retrofit market still hot?

A. According to a recent survey by the Mobile Air Conditioning Society (MACS), approximately 40 percent of the A/C work thats currently being performed is on older vehicles with R-12 A/C systems. Of these, about 9 percent were retrofitted this year to R-134a.

Most shops will encourage customers to convert their vehicles A/C system to R-134a if major A/C components such as the compressor, condenser or evaporator need to be replaced. Most new compressors and reman compressors are manufactured to be compatible with R-134a, so theres no penalty to retrofit the system if these parts are being replaced. On some older Japanese cars, the compressor seals are not compatible with R-12, which means the compressor must be replaced if the vehicles owner wants to change refrigerants.

Changing refrigerants requires recovering any old refrigerant that may still be in the A/C system, and replacing some or all of the old mineral oil in the system with the required PAG oil or POE oil.

Cooling performance with R-134a is nearly the same as R-12 on most vehicles, but some may require the installation of a larger or more efficient condenser and/or a variable orifice tube to improve low-speed cooling.

Another reason to convert is that R-134a costs less than R-12, which is becoming scarcer and more expensive as time goes on. Consumers can also purchase small 14-oz. cans of R-134a and recharge their own A/C system if the need arises, which is a plus for your do-it-yourself customers. Federal law restricts the sale of R-12 to certified professionals only.

The MACS survey also found that owners of older vehicles are still spending money to maintain and repair their A/C systems, and that many people are spending upwards of $1,000 or more to repair and retrofit older cars and trucks!

The average A/C repair job, according to MACS, was $504 for all types of service work, plus an average of $176 extra to retrofit the system after repairs were made.

Q. What kind of A/C parts are replaced most often?

A. According to the same MACS survey, these are the A/C system parts that are most often replaced:


  • 31 percent - Compressor (17 percent due to leakage, 14 percent due to internal failure);


  • 10 percent - Leaky hoses;


  • 8 percent - O-rings or seals;


  • 6 percent - Compressor clutches (worn out or failed);


  • 5 percent - Condenser (leaks, corrosion, damage, blockages);


  • 4 percent - Evaporators (leaks).

Knowing this may help you decide what kind of A/C parts to keep in stock.

Q. Is flushing recommended to clean dirty or blocked condensers?

A. Flushing is a controversial issue because some vehicle manufacturers endorse it, while others prohibit it. According to the MACS survey, one out of four vehicles that had A/C service work done also had their A/C system flushed either because the vehicle experienced a compressor failure or the system was contaminated with sludge or debris.

Most shops (92 percent) say they use liquid refrigerant to clean the A/C system, while 5 percent reported using an approved flushing chemical. No cleaning chemical other than one that has been approved for A/C flushing should be used to clean A/C parts. Many chemicals attack plastic parts such as orifice tubes, o-rings and hoses, and can leave harmful residues in the system that may later cause problems.

Whats more, only certain parts can be flushed. This includes serpentine-style condensers (but not parallel flow condensers), evaporators, hoses and lines. Compressors should not be flushed, nor should hoses that contain in-line mufflers or filters.

Flushing is good for removing sludge and debris from contaminated systems and for removing excess compressor oil from the condenser (if the system has been overcharged with oil, which is a common problem).

To help technicians better understand the flushing process, ACDelco has released a new A/C Flushing video (SD-AC-1.01-SUP) that is available through ACDelco distributors.

One caution with respect to flushing is that it will not remove all of the metallic debris from a contaminated system. An in-line filter should therefore be installed in the liquid line to trap any residual debris that a flush may have missed.

Q. Is dye the best way to find refrigerant leaks?

A. Ultraviolet dyes that are added to refrigerant can make even the smallest leaks clearly visible. But some vehicle manufacturers do not approve their use because they fear dye may cause problems. OEMs who currently endorse the use of dye include Ford, GM, DaimlerChrysler and Nissan. OEMs who do not currently use or endorse dyes include Honda, Mazda, Toyota, Hyundai and Mercedes. OEMs who do not use or endorse dye may not honor a compressor warranty if it fails and is found to contain dye.

Too much dye can dilute the compressor lubricant and increase the risk of compressor noise and failure. The standard recommended dose is only one quarter ounce. A second dose will usually cause no problems, but multiple doses over a period of time can overload the system with too much dye.

Q. Are A/C system sealers safe to use?

A. In recent years, various sealer products have been introduced to stop refrigerant leaks. Some are activated by exposure to moisture, while others stop leaks by causing seals and o-rings to swell. These products may also be used to temporarily seal evaporator pinholes and other leaks when a customer cant afford to have parts replaced.

In spite of these benefits, no OEM vehicle manufacturer currently approves of the use of any type of sealer in their A/C systems.There is some concern that sealers may gum up refrigerant recovery and recycling equipment, service hoses and test gauges. To address this issue, several companies have introduced filters to protect service equipment from sealers and dyes. Technicians often have no way of knowing if someone has added a sealer to an A/C system in an attempt to stop a leak.

Q. What about other kinds of refrigerants (other than R-12 and R-123a)?

A. Although many refrigerants have been approved by the EPA, they can never be mixed. Its illegal, potentially dangerous and can ruin a technicians AC service equipment. This includes R-134a: It cannot be mixed with R-12.

Mixing different kinds of refrigerants alters the operating pressures and can cause system problems such as a failed compressor.Of course, its okay to convert from one refrigerant to another, but before that can be done, all the old refrigerant must be evacuated (not vented) using the proper equipment.


Batteries

Q. Is cold weather harmful to batteries?

A. The chemical reactions inside a lead-acid battery are affected by temperature. As the temperature drops, it slows down the chemistry and reduces the number of cranking amps the battery can produce.

At zero degrees F, most batteries can only deliver about 65 percent of their normal cranking amps. At 20 degrees below zero, battery power is cut in half!

But when the temperature warms up again, the batterys ability to produce power returns to normal, and the battery produces the same number of amps as before.

Cold weather also increases the cranking load on the battery. Cold weather thickens the oil in the engines crankcase. This increases friction and makes the engine harder to crank. Normal cranking loads can require 125 up to 200 amps or more from the battery depending on engine displacement, compression and temperature. At zero degrees F, that number can increase 200 to 250 percent depending on the viscosity of oil in the crankcase.

Actually, hot weather is hardest on batteries because it increases the rate at which water evaporates from inside the battery.

Q. How do you determine a batterys state of charge?

A. Battery charge can be determined in several ways. Some batteries have a built-in charge indicator. If a green dot is showing in the clear plastic window, it means the battery is 75 percent or more charged. A dark indicator (no green dot) indicates a low battery that needs to be recharged and tested. A clear or yellow indicator means the water level inside the battery is low. The filler caps should be removed from the top of the battery so water can be added to bring the level back up to normal. The battery can then be recharged and tested. If the top of the battery is sealed, the battery should be replaced. Do not attempt to recharge a battery with low water because there is a risk of an explosion!

Battery charge can also be measured with a voltmeter. A fully charged battery should read 12.6 volts. A reading of 12.4 volts equals about a 75 percent charge and is good enough for further testing. But anything less means the battery is low and needs to be recharged.

If the battery has removable filler caps, charge can also be determined with a hydrometer that measures the specific gravity of the electrolyte inside the battery.

Lead-acid batteries must be maintained at or near full charge to prevent deterioration of the lead plates inside. If the battery is allowed to sit more than a couple of days in a discharged condition, the plates can become sulfated and may not fully recover when the battery is recharged. This will reduce the batterys output as well as shorten its service life.

Q. How can you tell if a battery needs to be replaced?

A. By testing it with a battery tester. If a battery is run down or dead, it may only need to be recharged. A tester will reveal if the battery can hold a charge or if it needs to be replaced.

Older-style carbon pile testers apply a fixed load to the battery while monitoring its voltage. For accurate test results, the battery must first be recharged - a process that may take half an hour to overnight depending on the chargers output and the rate at which the battery accepts the charge.

Warning: Do not attempt to recharge a frozen battery. The battery should be brought inside and allowed to thaw before it is recharged or tested.

Many electronic battery testers do not require a fully charged battery for accurate test results. Testers that measure the batterys conductance can reveal the batterys condition whether it is charged or run down. Conductance testers send a frequency signal through the battery to determine how much plate area is available to hold and deliver power. As a battery ages, its conductance declines. Shorts, opens and other cell defects also affect conductance, so measuring conductance gives an accurate indication of battery condition.

Many electronic battery testers also analyze the batterys cold cranking amp (CCA) capacity, which can be used to estimate the batterys remaining service life. Some also allow you to measure the amps drawn by the starter while cranking the engine and analyze the charging systems output under load once the engine is running. Some testers even provide a built-in voltmeter for checking connections.


Brake Materials

Q. What are ceramic brake pads?

A. The short answer is that they are pads that contain some type of ceramic fiber. The long answer is that there are literally hundreds of different friction formulas in use on vehicles today. These materials range from pads with high-content ceramic to low-metallic pads with some ceramic content to semi-metallic pads with no ceramic content. The exact recipes are all proprietary secrets, so there is no way to know how much ceramic content or what type of fibers are actually in a set of pads. All you can go by is what the brake supplier tells you on the packaging, product literature or advertising. Even then, the information thats provided may be confusing.

The term ceramic is badly misused and abused and can mean almost anything with respect to brake pads. Its like ordering pizza. Do you want mushrooms, pepperoni, sausage, extra cheese, thin crust, thick crust, hand-tossed, stuffed or what? Likewise, ceramic friction materials are all different. There are different types and shapes of ceramic fibers. Which fibers are used and how they are combined with other ingredients determines the noise, wear and braking characteristics of the friction material.

One brake supplier said that they use over 20 different ceramic formulas in their ceramic product line alone, while others use only a single ceramic formula. Those who sell single-formula ceramic linings typically suffer from high Mu Variability - thats engineering lingo for a lot of variation in hot and cold friction coefficients. This results in fluctuating stopping power as the brakes heat up. It can also lead to comebacks if your brake customer is unhappy with the way their brakes feel.

Some brake suppliers offer ceramic enhanced formulas that add a dash of ceramic to an existing conventional formula.

According to industry sources, ceramic linings are now used on 75 percent of 2004 cars and light trucks. But some linings are low-content ceramics, while others are high-content ceramics. Some formulas contain up to 30 percent iron to help dampen noise, while others use little or no iron.

Q. What are the advantages of ceramic pads?

A. It depends on the brand of ceramic pads and what is in them, but generally speaking, friction suppliers claim the following benefits for high-content ceramic pads:


  1. Quiet operation (typically much quieter than other types of friction materials, especially semi-metallics). One of the characteristics of ceramic fibers is that they dont ring like steel fibers. Annoying brake squeal is eliminated because the ceramic compound dampens vibrations.


  2. Smooth, rotor-friendly braking (less wear on pads and rotors).


  3. Cleaner braking (no black brake dust to dirty up alloy wheels).

Q. Can ceramic pads be installed on any vehicle?

A. The best advice here is to follow the friction suppliers recommendations. Ceramic replacement linings are available mostly for later-model vehicles. As a rule, most friction suppliers recommend replacing same with same or better.

If a vehicle is originally equipped with ceramic pads, it should have the same type of pads installed when the brakes are relined. Aftermarket ceramic pads that are application engineered will have friction characteristics very similar to the OEM pads, and should have similar noise, wear and braking performance.

As for vehicles that are originally equipped with nonasbestos organic (NAO) pads, upgrading to ceramics can often improve stopping power and pad life.

Vehicles that are originally equipped with semi-metallic pads, on the other hand, should probably stick with semi-metallic replacement pads. Semi-metallic linings are designed for high-temperature applications. For severe-duty use, other types of replacement pads might not stand up as well. For normal driving, switching to ceramic pads may help reduce noise and extend rotor life. Ceramics also require less pedal effort then semi-metallics.

Q. Whats the difference between economy-, standard- and premium-grade brake linings?

A. Price is one difference, but of course its not the only one. Premium-grade replacement linings cost more because they generally provide better wear than standard-grade linings, and certainly much better wear than economy-grade linings. Premium linings also tend to perform better in terms of stopping distance, fade resistance, pedal feel and noise control. As a rule, premium linings will restore the like-new feeling and performance that makes most customers happy.

Brake suppliers use different grades of friction materials in their economy, standard and premium product lines - and that affects the price.

Economy linings are for bargain-shoppers who want a quick fix and little else. Economy linings should never be installed on a vehicle that has a history of eating up pads or is obviously a hard-use application. Economy linings will not provide the same durability as standard- and premium-grade linings, and may not feel, sound or stop the same as the OEM linings. Economy product lines typically use only a few friction formulas, or even a one-size-fits-all formula. But in the real world, one-size-fits-all fits some better than others. There are always compromises because of differences in vehicle platforms, braking systems, weight and usage.

Standard linings, by comparison, are for normal-duty users and provide good value for the money. They may or may not use the same basic type of friction material as the OEM linings, but they generally provide satisfactory performance.

Premium linings typically use a greater variety of friction formulas for different vehicle applications. This is called application engineered or application specific lining selection. The product engineers who develop and choose the friction materials try to closely match the braking performance, feel and noise qualities of the original equipment linings and the vehicle platforms they come on. Their goal is to equal or exceed OEM braking performance.

Premium linings cost more because of this, but are also more profitable to install for your professional customers - and experience fewer comebacks because of noise, pedal feel and performance complaints.

And thats important. According to one JD Powers survey, the most important things that brake customers want are in the following order:

1. Stopping power;
2. Good pedal feel (no soft pedal);
3. Quiet operation (no squeals or other objectionable noise);
4. No brake pulsation (which is a function of rotor wear and runout);
5. Durability.

Q. What causes brake squeal?

A. High-frequency vibrations. When the brakes are applied and the pads contact the rotors, tiny surface irregularities in the rotors act like speed bumps causing the pads to jump and skip as they scrape against the rotors. This, in turn, causes the pads to shake and vibrate in the calipers and against the caliper pistons. It also causes the calipers to shake and vibrate on their mounts and bushings. The greater the play between all of these parts, the greater the amplitude of the vibrations and the louder the squeal.

Semi-metallic pads tend to be noisier than ceramic, low-metallic and nonasbestos organic (NAO) friction materials. The sound qualities of any friction material depends on the fillers, lubricants and other ingredients that go into the mix. Some manufacturers add graphite and other materials to pads to dampen noise.

The design of the pads also influences their ability to suppress noise. If the leading edge of the pads has a sharp edge, it increases the tendency to grab and bounce more than if the leading edge is chamfered. Thats why most premium-grade brake pads have chamfered edges. The pads may also have a slot down the middle to increase flexibility, cooling and venting. Some pads also have integrally molded shims and a multi-layer construction to reduce noise.

Some friction suppliers use Transfer Film Technology (TFT) to prevent noise. TFT is not a coating on the pads but part of the friction material itself.

As the pads wear, they continuously transfer a very thin film to the rotor surface. This film, which leaves a dull gray coating on the rotors, fills in tiny imperfections in the rotor surface to make it smoother and more compatible with the pads, thus eliminating squeal-producing vibrations.

The rhythmic vibrations of the pads rubbing against the rotors also creates harmonic vibrations in the rotors that causes them to ring like a cymbal. Researchers have found that rotor vibrations are not uniform all the way around a noisy rotor. The rotor has certain spots or nodes that oscillate more than other areas. By redesigning the casting and changing the location of the cooling fins between the rotor faces, some of this noise can be tuned out (a good reason to use replacement rotors that have the same cooling configuration as the original.)

Even the metallurgy of the rotors makes a difference. Some grades of cast iron are quieter than others.

Rotor finish also affects noise. The smoother and flatter the surface, the less the likelihood of the pads chattering and dancing as they ride across the surface. The rotors should be resurfaced when the linings are replaced if the rotors are not smooth and flat. Light sanding with a flexible abrasive brush after the rotors have been turned will improve the surface finish even more and provide an extra degree of assurance that the rotors will remain noise-free.


Engine Management

Q. If a vehicles Malfunction Indicator Lamp is on, will reading the Diagnostic Trouble Code (DTC) with a scan tool tell me which part needs to be replaced?

A. Indirectly it can, but the code by itself only tells you which circuit or system is involved. Whats more, some codes only describe a condition and dont give you any clues as to what might be the cause.

A cylinder misfire code, for example, tells you a cylinder is misfiring but does not tell you why or which parts may be involved. The misfire may be caused by a worn or fouled spark plug, a bad plug wire, a weak or faulty coil if the engine has a distributorless ignition system with multiple coils, a dead or plugged fuel injector, a burned exhaust valve that is leaking compression, or a leaking head gasket. Any of these can cause a misfire, so additional diagnosis is needed to isolate the fault before any parts can be replaced.

Q. What is flash reprogramming?

A. Its a technique for updating or recalibrating a vehicles Powertrain Control Module (PCM), or any other onboard module that has this feature can be accessed with a specially-equipped scan tool. Flash reprogramming is done to cure driveability and emissions problems, to calibrate new and reman PCMs, and to change fuel and ignition curves and other functions for performance applications.In the early 1990s, some vehicle manufacturers began adding Electronically Erasable Program Read Only Memory (EEPROM) chips to the circuit boards of their PCMs. Prior to this, the only way to change the PCMs programming was to physically remove the old PROM chip and install a new one.

With programmable PCMs, updates and changes can be installed electronically in a matter of minutes using a pass-through scan tool, a personal computer and new software downloaded from the vehicle manufacturer. If a PCM is being custom modified for a performance application, the software changes would be made by somebody who knows how to hack into the PCM using special access codes. This requires a high level of expertise and is not approved by the OEMs.

There are also special aftermarket performance scan tools that allow a user to get into a PCM and play around with the spark advance, fuel mixture and other functions such as the engine rev limiter, vehicle speed limiter, torque converter lockup, etc. The tools are available from several camshaft manufacturers and are necessary to make changes to the PCM when a performance cam is installed in an engine.

Some remanufacturers who supply reconditioned PCMs now flash program PCMs for specific vehicle applications. But to do this, they need three critical pieces of information: the vehicle identification number, the type of transmission and the emissions type.

Q. What do I need to flash reprogram a PCM?

A. You need three things: a scan tool or J2534 pass-through device that is flash capable; a Windows 98 or higher PC with a modem and Internet access for downloading the flash software from the vehicle manufacturers website; and a subscription to the manufacturers database so you can access the software. Other items that are needed include a cable to connect the PC to the scan tool or J2534 pass-through device, and a cable to connect the scan tool or J2534 pass-through device to the OBD II connector on the vehicle.


  • For GM applications: you need a Tech 2 scan tool or Vetronix Mastertech, or aftermarket scan tool with flash capability.


  • For Ford applications, you need a Ford New Generation Star (NGS) scan tool, or aftermarket scan tool with flash capability.


  • For Chrysler applications, you need a Diagnostic and Reprogramming Tool (DART). Chrysler dealers use the Mopar Diagnostic System (MDS2) and DRB III scan tool. Or, you can use an aftermarket scan tool with flash capability.


  • For import applications, you need whatever factory scan tool the dealer uses, an aftermarket scan tool with reflash capabilities for that vehicle, or a J2534 pass-through device that will work on the vehicle.

The flash procedure usually takes only a few minutes and is similar to installing new software into a computer. The only difference is that youre downloading the new software through a modem and scan tool into the vehicles PCM through the OBD II diagnostic connector.


Exhaust

Q. Which parts in the exhaust system are most likely to fail?

A. Drive any vehicle long enough, and it will eventually need a new muffler, exhaust pipes and converter. The more the parts are exposed to road salt, moisture, road hazards and severe vibration, the more likely they are to fail.

Exhaust system parts live in a very corrosive environment. The hot exhaust gases that exit the engine pass through the catalytic converter where some of the byproducts of combustion are changed into sulfuric acid. The acid combines with the moisture in the exhaust and eat away at the muffler and pipes from the inside out. Especially vulnerable to this type of corrosion are mufflers and resonators located behind the rear wheels where exhaust temperatures are cooler and the potential for corrosion is higher. When the engine is shut off, the gases cool, condense and puddle inside the system eating away at the metal from the inside out. Short-trip driving is especially hard on the exhaust system because it never gets hot enough to dry out all the moisture.

The stainless steel exhaust systems that are used on many late-model cars and trucks are corrosion-resistant and may last seven to 10 years before they fail. Theyre covered by a new car bumper-to-bumper 3/36 warranty, but beyond that, anything can happen. Catalytic converters are under warranty for eight years or 80,000 miles.

Heat and vibration from normal driving is also hard on pipes, connectors and flanges. Stainless steel resists corrosion, but it is also hard and brittle. Its not unusual for fatigue cracks to form that eventually lead to exhaust leaks.

With transverse-mounted engines, the head pipe must have some type of flexible coupling or section to handle engine movement. Many failures occur in this area because this is the most highly stressed part of the system - and also one of the most expensive to replace. Head pipes with flex sections are commonly used on import vehicles and have a high failure rate.

Q. Why are exhaust leaks so dangerous?

A. Ever heard of carbon monoxide? Its an odorless, invisible gas that is a byproduct of combustion - and it can kill in minutes!

It doesnt take much carbon monoxide to make a driver dizzy or cause him to pass out. Fumes that enter the passenger compartment can be deadly, so warn anyone who has an exhaust leak what theyre risking and to make the necessary repairs.

Leaks can occur anywhere from the exhaust manifold gaskets to the tailpipe. Exhaust manifold leaks are quite common and occur because the gasket has failed from thermal stress and scrubbing. A customer who is replacing an exhaust manifold gasket will probably also need new exhaust manifold bolts.

Q. Exhaust noise from the engine compartment usually means what?

A. A leaky exhaust manifold gasket, a cracked exhaust manifold or a leaky head pipe connection. Cracks in exhaust manifolds are a common problem on some engines. An exhaust manifold goes from stone cold to hundreds of degrees in a matter of seconds when an engine is first started. Stomping on the throttle and working the engine really hard sends manifold temperatures soaring. This puts a lot of thermal stress on cast manifolds, which eventually leads to cracks and exhaust leaks. Cast iron does not weld very well in this kind of application, so the best fix is to replace the manifold with a new one. New manifolds should always be installed with new gaskets and bolts.

Q. Whats the number one killer of catalytic converters?

A. Ignition misfire. A single misfiring spark plug can allow enough unburned fuel into the exhaust to overheat and damage the converter. It can make the converter run so hot that the catalyst inside the converter melts causing a partial or complete blockage in the exhaust system.

Theres no way to clean or unplug a damaged converter. Replacement is the only fix. But a new converter should not be installed until the underlying cause of the failure has been diagnosed and repaired. The cause may be a fouled spark plug, bad plug wire or dead coil on an engine with a distributorless ignition system or coil-on-plug ignition.

Converter overheating can also be caused by a burned or leaking exhaust valve that allows unburned fuel to pass through the engine.Contamination is another common cause of converter failure. Contaminants include phosphorus from burning oil (worn valve guides or seals, or worn piston rings or cylinders), silicone from internal coolant leaks (bad head gasket or cracks in combustion chamber) and high levels of sulfur in gasoline.

Replacement converters must be the same basic type as the original (two-way, three-way or three-way plus oxygen), and be installed in the same location in the exhaust system. Replacing a converter with a straight pipe or test pipe is illegal.


Fuel Pumps

Q. How much fuel pressure should a good fuel pump produce?

A. It depends entirely on the vehicle application and fuel system.

Fuel-injected engines require a lot of pressure to operate the fuel injectors. The pump has to push fuel from the tank to the injector supply rail on the engine, and then force it through each injector when the injector opens to spray fuel into the engine. The amount of pressure is critical and must be within specifications for the injectors to deliver their normal dose of fuel. The amount of pressure required may vary from 35 to 85 pounds of pressure depending on the system, application and load on the engine.

On older carbureted engines with mechanical fuel pumps, much less pressure (2 to 6 lbs.) is needed because all the pump has to do is keep the carburetor bowl filled with gasoline. Intake vacuum sucks the fuel through the carburetor.

What happens if fuel pressure is not within specifications? Too much fuel pressure in a fuel-injected engine will create a rich fuel condition, causing an increase in fuel consumption and carbon monoxide (CO) emissions. An engine thats running really rich may also experience a rough idle, surging and possibly even carbon-fouled spark plugs.

Not enough fuel pressure can starve the engine for fuel, creating a lean fuel condition. This can cause hard starting, misfiring, rough idle and loss of power.

If theres no pressure because the pump has failed or is not running, the engine will crank normally but wont start.

Q. What causes electric fuel pumps to fail?

A. Dirty fuel, normal wear and running out of gas. Most outright pump failures are caused by fuel contamination such as dirt, rust or hose debris from deteriorating braided fuel lines. The pump pickup inside the fuel tank has a filter sock or screen to keep large pieces of debris out of the pump and fuel line, but smaller pieces can pass right through.

Normal wear is also a factor. Fuel pumps run constantly, so over a number of years they can experience wear not only in the armature bushings and vanes but also the brushes and commutator. Electric fuel pumps rely on the fuel passing through them for lubrication and cooling. Any junk thats in the gasoline will therefore accelerate the normal wear process and shorten the life of the pump.

Pump failure can also occur if the sock becomes clogged and starves the pump for fuel. With no lubrication, the pump can run hot and self-destruct.

Testing a fuel pump involves measuring fuel pressure while the engine is running. Many fuel-injected engines have a pressure test fitting on the injector supply rail for this purpose.

Another method is to disable the ignition, disconnect the fuel supply hose from the injector rail and energize the pump to see how much fuel it delivers. As a rule, a good pump will deliver at least 750 ml (3/4 quart) of fuel in 30 seconds.

If a pump fails to run, a check should be made to see if it is receiving normal battery voltage. The pump motor itself can be checked with an ohmmeter. As a rule, most pumps should read 2 to 50 ohms if good. If the pump is open (reads infinity) or shows zero resistance (shorted), then the motor is bad and the pump needs to be replaced.

If a pump motor runs but system pressure is low, the problem might be a faulty fuel pressure regulator. The regulator is usually mounted on the injector supply rail. Its job is to vent pressure and route excess fuel back to the tank when system pressure exceeds specifications. The regulator is connected by a vacuum hose to the intake manifold so it can balance pressure according to engine load.

A plugged fuel filter can also obstruct the flow of fuel and cause a drop in pressure.

Q. Do replacement electric fuel pumps have to be identical to the original?

A. A replacement pump must have the same pressure and flow ratings as the original, but the type of pump (single or double-vane, roller vane, turbine or gerotor-style pump) and its external appearance may vary depending on the supplier.

The pump is usually mounted inside the tank and is part of the fuel gauge sending unit. The pump can usually be replaced separately, but on some vehicles the whole assembly must be replaced. Complete assemblies are also available for many applications where the pump alone can be changed because a complete assembly is faster and easier to install, and reduces the risk of a comeback due to improper installation.

When a tank-mounted pump is replaced, the inside of the tank should always be inspected and cleaned if there is evidence of rust or debris in the pump or filter. Replacing a pump without cleaning a dirty tank will doom the new pump to premature failure.

When the pump is changed, a new pickup sock should also be installed along with a new inline fuel filter.

Warn your customers not to test a new pump before it has been installed by jumping it. Running a pump in a dry condition with no fuel to lubricate it may damage the pump.

Q. My customer replaced his fuel pump, but his engine is still not getting any fuel. Whats wrong?

A. The problem could be one of several things. It could be a lack of voltage to the pump (check the pump wiring, ground connection and power relay). It could be a plugged fuel filter or fuel line. Or, it could be a bad powertrain control module (PCM) or safety switch.

When the driver turns the key on, the PCM routes power through a relay to energize the pump. On some vehicles, there is a device called an inertial safety switch that is designed to turn off the fuel pump in the case of an accident. A severe jolt may have tripped the safety switch and opened the power circuit to the pump. Refer to the vehicles wiring diagram for the location of the safety switch (if equipped).

Power relay failures are a common cause of fuel pumps that dont work. The relay may be located under the instrument panel or in the engine compartment. Refer to the vehicles wiring diagram for its exact location. No voltage at the pump terminal when the key is on and the engine is cranking would indicate a faulty pump relay, PCM relay driver circuit or a wiring problem. Check the pump fuse to see if its blown. If voltage is reaching the relay from the PCM but the relay is not closing and routing voltage to the pump, the relay needs to be replaced.

As for the pump itself, loose, damaged or badly corroded wiring connections can prevent the needed volts from reaching the pump motor. The connectors are located under the vehicle and may be vulnerable to road splash and vibration.

One check that can be made is to use an ohmmeter to check pump continuity. As a rule, most pumps should read 2 to 50 ohms if good. If the pump is open (reads infinity) or shows zero resistance (shorted), theres a wiring problem or the pump motor is bad.

If the pump runs when the ignition is turned on, but the fuel is not reaching the engine, a plugged fuel filter or fuel line is probably the cause of the no-start condition. Many vehicles today do not have a recommended replacement interval for the fuel filter, so its likely the filter may never have been replaced. Over time, the filter will gradually plug up creating a restriction that may block the flow of fuel to the engine. Any rust or sediment in the fuel tank will obviously add to the clogging problem.

Q. If a pump has failed because of contamination, or the filter is clogged, should the fuel tank be replaced?

A. A dirty fuel tank can be drained and steam cleaned to remove contaminants, but a tank thats rusty inside or leaking should always be replaced.

Cleaning may dislodge and temporarily remove the loose rust, but sooner or later more rust will appear and flake loose into the fuel. After 10 or more years of service, the protective plating on the inside of many steel gas tanks is no longer able to prevent rust. High humidity, exposure to road salt and not keeping the tank full can all accelerate the formation of rust inside and outside the fuel tank.


Gaskets

Q. What are graphite head gaskets?

A. Graphite head gaskets contain a layer of graphite, which is a high-temperature anisotropic material that dissipates heat from hot spots that form around the combustion chambers. Too much heat can crush an ordinary gasket causing the gasket to fail, so graphite head gaskets are used in many late-model, high-output bimetal engines (aluminum heads/cast iron blocks). Graphite head gaskets are also available as an upgrade for many older engines and for high-performance engines.

Graphite is easy to identify because of its silver color. It also feels slippery. This allows the gasket to handle movement that occurs between the head and block in bimetal engines (aluminum expands at a rate that is 1.7 times greater than cast iron as it heats up.) Graphite is also a relatively soft material that provides a good cold seal when the gasket is first installed.

Q. What are MLS head gaskets?

A. MLS stands for Multi-Layer Steel. These gaskets are made of several layers of steel (typically three to seven.) The outer layers are usually stainless spring steel and have embossing (raised beads) to improve sealing. The outer layers are also coated with a thin layer (.001 to .0015 in.) of nitrile rubber or Viton to improve cold sealing. The inner layers of an MLS gasket are flat and provide added support and thickness.

MLS head gaskets are used on a growing number of late-model engines, including many Japanese applications as well as the Ford 4.6L V8 and other Ford, Chrysler and GM engines. MLS gaskets are also available as an upgrade for certain problem engines such as the early Neon 2.0L that were not originally equipped with this type of gasket. MLS head gaskets are also used in NASCAR racing engines and are available for certain high-performance applications as well.

The multi-layer all-steel construction makes MLS gaskets very durable and highly resistant to burn-through. The gaskets also retain torque well and wont take a compression set like an ordinary head gasket. The design also requires less clamping force on the head bolts, which reduces cylinder bore distortion for reduced blowby and emissions. But MLS gaskets are more expensive to manufacture and require an extremely smooth mirror-like finish on both the cylinder head and engine block to seal properly.

To achieve proper loading, most MLS gasket applications also require a special type of head bolt called a torque-to-yield (TTY) bolt. TTY head bolts are typically longer and narrower than ordinary head bolts and stretch slightly when tightened. Most vehicle manufacturers say TTY head bolts should only be used once, and should always be replaced with new TTY bolts when the head gasket is changed.

If new head bolts are not included in a head gasket set, be sure to recommend them to your customer.

Tough as MLS gaskets are, they cannot be reused. Once installed, the embossed surfaces are permanently deformed and will not reseal properly if the gasket is reused. One use is it. If the cylinder head comes off the engine for any reason, a new MLS head gasket must be installed.

Q. What would cause a head gasket to fail after it has been replaced?

A. Some engines, because of the design of their cylinder heads and bolt patterns, are hard to seal. If the OEM-style head gasket is not durable enough for the application, it wont hold up. There have been a number of engines that fall into this category including Oldsmobile 2.3L Quad Four, Ford 3.8L V6, early Neon 2.0L, Toyota 22R, Honda 1.5L and 1.7L and others. Upgrading to an aftermarket graphite or MLS-type replacement gasket may be the only way to prevent repeat gasket failures on some of these engines.

Head gasket failures can also occur if the sealing surfaces are not clean, smooth and flat. There should be no gasket residue, grease, dirt or oil on either surface. The surface finish on the head and block must both be within the recommended range to seal properly. For most OEM MLS gaskets, the magic numbers are 20 to 30 microinches, but there are now aftermarket MLS gaskets that can handle surfaces finishes as rough as 60 microinches RA. The standard recommendation for most non-asbestos composition head gaskets on a cast iron engine is 60 to 125 microinches. For bimetal engines, a smoother finish of 30 to 60 microinches is recommended.

Flatness is also important for a good seal. There should be no more than .002 inches out-of-flat sideways across any cylinder head or block surface, and no more than .003 inches out-of-flat lengthwise in a V6 head, .004 inches in a four cylinder or V8 head, or .006 inches in a straight six head. The head and/or block should be resurfaced if they are not within flatness specifications.

Most head gaskets are installed dry. Sealer should not be used on a coated gasket because the sealer may damage the coating material.

Finally, increasing an engines compression ratio, and/or making performance modifications that significantly boost the engines horsepower output will also increase the load on the head gasket. For these kind of applications, your customer may have to upgrade to a stronger racing-style head gasket with thicker stainless steel combustion chamber armor and other features that help it withstand higher loads. Some racers use solid copper head gaskets. This usually requires machining the block for o-rings to seal the combustion chambers. Special coatings or sealer may also be required to seal copper head gaskets.

Q. Why are some replacement head gaskets thicker than a stock gasket?

A. To compensate for head resurfacing. Some aftermarket gaskets may be .020 to .030 inches thicker than a standard or stock replacement head gasket to make up for metal that may have been milled off the cylinder head or block deck.

The thickness of the head gasket affects the compression ratio. This, in turn, affects the engines octane requirements and its ability to resist engine-damaging detonation (spark knock). If the cylinder head was resurfaced to restore flatness and/or the surface finish, it may be necessary to use a thicker head gasket to maintain the same compression ratio as before.

A thicker gasket can also be installed to lower compression slightly and reduce the risk of detonation. On overhead cam engines, it can also help restore stock valve timing if the head has been milled.

Head gasket shims are another product that can also be used for the same purpose. Installing a .020-inch thick shim under a stock head gasket can raise the head enough to restore proper valve timing and compression. Both copper and steel shims are available for a wide range of applications. Most shims require a brush-on or spray-on tacky sealer on the underside that faces the block, but no sealer should be used on the top side that faces the gasket.

Another product thats now available for a few Honda engines is an adjustable head gasket. This is a multi-layer MLS head gasket with stackable shims that can be added to vary the engines compression ratio. The compression ratio of a turbo-charged engine can be reduced by adding layers when the gasket is installed.


Hoses

Q. Why are hoses so important?

A. Hoses carry coolant, fuel, vacuum and vapors, all of which are needed to keep a vehicle running. The radiator and heater hoses carry coolant between the engine, radiator and heater. Fuel hoses attach the lines that carry fuel from the fuel tank to the engine. Vacuum and vapor hoses connect the intake manifold, throttle body and fuel tank to various sensors, the PCV system, power brake booster, charcoal evaporative emissions canister and cruise control system.

A hose failure in any of these systems may result in anything from a breakdown to an emissions failure to a fire.

Most motorists totally ignore the condition of their vehicles hoses until one fails. Then they suffer the consequences. A leaky radiator or heater hose will lose coolant and eventually cause the engine to overheat. This may result in expensive engine damage. A fuel hose failure may cause the engine to stall, or worse yet, spray fuel on a hot engine causing a fire. A leaky vacuum hose or vapor hose may cause driveability and emissions problems, or loss of brake assist if it happens to be the hose that routes vacuum to the brake booster.

So dont think for a minute that hoses are not important. They are extremely important and should be inspected regularly - and replaced if found to be leaking, cracked, chaffed or damaged.

Q. How often should radiator and heater hoses be replaced?

A. There are no official scheduled maintenance recommendations for replacing hose, but that doesnt mean they last forever. Any hose thats made from natural or synthetic rubber will oxidize and harden with age and exposure to high operating temperatures. The lifespan of a coolant hose depends on the hoses location in the engine compartment and its exposure to heat and oil contamination. Coolant hoses can also undergo internal deterioration as a result of electrolytic corrosion. Thats why hoses should be checked on a regular basis and replaced periodically.

Many hose manufacturers still recommend replacing coolant hoses every four or five years for preventive maintenance because the incidence of failure rises sharply after the fourth year of service.

Unfortunately, few motorists today appreciate or practice preventive maintenance. Many wait for a hose to fail rather than replace it unnecessarily. Thats why we see vehicles stranded along the road with coolant and steam running out from under the hoods. The owners waited too long to replace old hoses.

Hoses can be checked for age hardening (or softening) by pinching. Any hose that feels rock hard or mushy is overdue for replacement. Visible cracks, blistering or any other visible damage on the outside of the hose would also indicate a need for replacement.

Replacement radiator hoses may be universal or molded to shape, and may require some trimming to length. Heater hose is usually cut to length from a roll. The overall length and the the size of both ends (which may be different on some radiator hoses) must be identical to the original for a proper fit. A hose that is too short may pull loose or rip as a result of normal engine movement. A hose that is too long may rub or chafe. The clamps should also be replaced when new hoses are installed.

Q. Why do different applications require different kinds of hose?

A. Coolant, gasoline and oil vapor are all different substances that require a different type of hose material that is chemically compatible. Pressure and vacuum also require hoses of varying strength and thickness. Thats why different types of hose are used in different applications.

Power steering hoses that connect the power steering pump to the steering gear, for example, must withstand oil and high pressure. The supply hose must be able to handle hundreds of pounds of pressure, but the return hose is low pressure and doesnt have to be as strong.

Fuel, emissions and vacuum hoses are also made of special materials to withstand the liquids and vapors they carry. Fuel-injected engines require high pressure-rated fuel hose. Fuel hose that is approved for older carbureted engines should not be used on high-pressure fuel injection systems. Many EFI systems operate at pressures up to 86 psi or higher, which is more than low-pressure hose is rated to handle. The pressure rating will often be printed on the hose itself.

Clamps should also be replaced when changing hoses. OEM spring clamps lose tension with age and may not squeeze a hose tightly enough to provide a leak-free seal.

Q. How do I know if a customers hoses need to be replaced?

A. When inspecting hoses, pinch each hose in different places. There should be some springiness, and the hose should immediately return to its normal shape. Carefully look at the hose and notice the signs of impending failure.


  • Cracks and Breaks

    Cracked or broken areas on the hose indicate that it might be dangerously close to a blow out. Oftentimes, these cracks will start at the end of the hose, where it is compressed from sealing.


  • Hardness

    Hoses should be soft and plyable. But over time, heat and age can cause the hose material to lose its suppleness and flexibility. Engine vibrations too can cause sudden ruptures, even when cracks are not visible.


  • Buldges and Swelling

    Grease and oil can cause rot when they splatter on hoses. The hose looses flexibility, cannot withstand pressure and, consequently, fails.Also, bits of rubber can flake off on the inside of the hose and clog up the cooling system, leading to radiator problems and over heating.


  • Worn Clamps

    If old hose clamps are used to secure new hoses, they may not be able to be tightened properly, which could result in leakage and hose failure. When selling a set of hoses, always sell new clamps as well.


Radiators

Q. Why do most vehicles today have aluminum radiators?

A. Aluminum is less expensive to manufacture and lighter than copper/brass, and it requires no lead solder. Lead is a heavy metal and is an environmental hazard as well as a potential health risk to people who manufacture and rebuild radiators.

Actually, copper/brass conducts heat somewhat better than aluminum, so a radiator made of copper/brass would cool better than one made of aluminum if both were the exact same size and thickness. To compensate, aluminum radiators may have more fins per inch and/or be thicker or have additional rows of tubes to increase cooling efficiency.

New manufacturing processes can create copper/brass radiators without any lead in them. In copper/brass radiators, the tubes are typically made of brass (which is 70 percent copper and 30 percent tin), while the fins are mostly copper. The tubes are joined to the fins and end headers with solder (either tin/lead alloy or a high tin alloy), or brazed with a copper filler material. Some radiator suppliers offer a choice of aluminum or copper/lead for replacement applications, while others only offer one material or the other depending on their manufacturing capabilities.

Initially, aluminum radiators were not as resistant to corrosion as copper/brass. But thanks to improvements in radiator manufacturing and better corrosion inhibiting additives in todays coolants, aluminum radiators now last 10 years or more without a leak.

Q. Do bigger or more powerful engines always need larger radiators?

A. Generally speaking, yes. The more horsepower an engine produces, the more waste heat it makes and the larger the radiator must be to handle the heat and prevent the engine from overheating. A larger radiator may mean wider, taller and/or thicker (more rows of tubes) to increase cooling capacity, or a more efficient design.

For high-performance applications, a fin count of 12 to 16 fins per inch is often required. Serpentine-style radiators are sometimes used to improve cooling because they can be manufactured with more fins per inch. Louvered fins can also improve heat transfer for better cooling.

Almost one third of the heat energy thats produced by combustion is absorbed by the block, pistons and cylinder heads. To keep the engine from getting too hot, the cooling system circulates coolant through the block and heads, and then routes it to the radiator. Air flowing through the radiator cools the liquid, lowering its temperature by a hundred degrees or more. The coolant is then recirculated back through the engine by the water pump to provide continuous cooling as long as the engine is running.

To cool efficiently, the radiator must be clean, in good condition and receive adequate airflow. The radiators front-mounted location ensures good airflow when the vehicle is in motion, but at low speeds and when the vehicle is stopped, a cooling fan must be used to boost airflow.

Q. Should a leaky radiator be patched or replaced?

A. If a radiator is leaking, it must be repaired or replaced to stop the loss of coolant. Even a tiny leak that seeps only a few drops a day will eventually allow enough coolant loss to make the engine run dangerously hot. The capacity of many cooling systems today is only a couple of gallons, so any loss of coolant greatly increases the risk of overheating, boilover and possible engine damage.

When selling a radiator, the most important considerations are sizing the radiator correctly and making sure the inlet and outlet fittings are in the right locations so the hoses will line up the same as before. The height and width are the most critical dimensions so that the radiator will fit properly. Some replacement radiators may be somewhat thicker or thinner than the original, but as long as it provides the same degree of cooling (or better) than the original, it would work fine.

Its extremely important to give every new radiator a clean start in its service life. That means flushing the cooling system and replacing all of the old dirty, contaminated coolant with new coolant.

Other items your customer will probably need include a new radiator cap (make sure the pressure rating is the same as the original), antifreeze, and new upper and lower radiator hoses, and clamps. If the vehicle is more than six years old and/or has overheated, you should also recommend replacing the thermostat.


Reman Calipers

Q. What are some reasons for replacing brake calipers?

A. Brake calipers must be replaced if they are sticking, leaking or damaged. Many brake technicians also recommend replacing high-mileage calipers even if they are not sticking or leaking to reduce the risk of future brake problems and to restore the brake system to like-new condition.

The calipers are a vital part of a disc brake system because they squeeze the pads against the rotors when the driver applies the brakes. Over time, the piston seal(s) in a caliper can wear out or crack. Once the seal goes, the caliper will leak brake fluid. This can lead to a loss of pressure in the brake circuit and brake failure. It will also ruin the brake pads.

Many calipers are floating calipers that move in and out on bushings or slides when the brakes are applied and released. This allows the caliper to center itself over the rotor so that both pads will work with equal pressure against the rotor. If corrosion or wear prevents the caliper from sliding, it may cause one pad (usually the inner one) to work much harder than its companion. The result is reduced braking effort and uneven pad wear.

The same condition may also cause one of the pads to drag against the rotor when the brakes are released. This may cause a steering pull to one side and will accelerate wear on the pad thats dragging.

If the pads are wearing unevenly, the caliper should be inspected to determine the cause. If the caliper mounts are worn, damaged or badly corroded, the caliper must be replaced.

Sometimes the piston(s) in a caliper can stick because of corrosion or dirt that has gotten past the outer dust seal. This will often prevent the caliper from releasing fully causing the brake to drag. Calipers with steel pistons are more vulnerable to this kind of problem than those with phenolic pistons, but there have been instances where phenolic pistons absorb moisture, swell up and stick, causing the caliper to freeze up.

As a rule, calipers are generally replaced in pairs - even if only one is leaking. The only exception would be a low-mileage vehicle where one caliper failed because of a flaw or damage. In high-mileage vehicles, both calipers have the same miles, so if one is leaking, the other will probably start to leak before long.

Q. Which is better, bare calipers or loaded calipers?

A. Neither. The only difference is that loaded calipers come with new pads and hardware. Bare calipers do not. Brake technicians typically prefer to install loaded caliper assemblies because they get all the parts they need in one box. There are no worries about mismatched brake parts, and there are fewer comebacks because of noise, rattles or other caliper/friction-related problems.

To avoid a mismatch of friction side-to-side, both calipers should be replaced at the same time if a customer is installing loaded calipers on a vehicle. If only one caliper is being replaced, they should use the same friction pads on both sides.

Q. Which is better, new or reman calipers?

A. Neither. The only physical difference is that a new caliper comes with a new casting. Remanufactured calipers reuse the original casting to reduce cost and include a new piston(s) seal and hardware. Reman calipers meet all OEM specifications and perform the same as new on the vehicle.

Q. What else needs to be replaced when changing a caliper?

A. Possibly the brake hoses that connect the calipers to the brake lines and the brake fluid. Hoses, like seals, do not last forever. For this reason, the hoses are often replaced along with the calipers when doing a brake job on a high-mileage vehicle.Brake hoses have a double-wall construction with an outer layer that serves as a shield for the inner liner that carries the fluid. If a hose is found to be cracked, leaking or damaged, it must be replaced. The same goes for a weak hose that balloons when the brakes are applied.

A hose failure can be very dangerous because the loss of brake pressure in the line will cause the brakes to fail.

Hoses also deteriorate internally. The rubber lining inside can flake loose and plug the line, which can prevent the brakes from applying or releasing. Pieces of rubber can also pass into the caliper or back to the master cylinder and cause additional problems.

When a caliper, hose, wheel cylinder or other part of the hydraulic system is replaced, the brake fluid should also be changed at the same time. Brake fluid absorbs moisture over time which lowers the fluids boiling temperature and increases the risk of brake fade and corrosion.

Q. Why do some brake calipers have phenolic pistons while others have steel pistons?

A. It depends on what the original equipment manufacturer or rebuilder chooses to use. Phenolic pistons are 80 percent glass fiber bonded together with phenolic resin, the same type of binder thats used in brake pads and clutch linings. Phenolic pistons are light weight, wont rust or corrode like steel, doesnt transmit heat to the brake fluid, and they have a greater amount of roll back when the brakes are released which helps reduces brake drag. Steel pistons, on the other hand, are stronger and can take more abuse. They also help pull heat away from the pads.

Phenolic pistons and steel pistons have both been used since the 1970s in brake calipers. So have aluminum pistons.

Ford and Chrysler vehicles have used phenolic pistons almost exclusively. General Motors, on the other hand, has used mostly steel pistons in the calipers of its vehicles over the years. The same is true for many import vehicle manufacturers.

Q. Ive heard that phenolic pistons sometimes swell up and stick. Is this true?

A. Phenolic pistons do swell slightly because the material is hygroscopic (absorbs moisture). But most of the swelling occurs immediately after manufacturing and is limited to about a .001 to .002 inch dimensional change. By compensating for this with increased manufacturing tolerances, sticking should not be a problem in normal use. Some Chryslers back in the 1970s had phenolic pistons that would swell up and stick because of moisture contamination, but thats ancient history.

Q. Can phenolic pistons be reused in a rebuilt caliper?

A. Yes, provided they are undamaged. Phenolic pistons are brittle and can be damaged by careless handling during disassembly. But if handled with care, they can often be reused.

Phenolic pistons can sometimes develop a slight bellmouth shape when the pads wear down and the piston protrudes from its bore. In such instances, the piston would not be reused.

With steel pistons, its a different story. By the time a caliper needs to be rebuilt, the steel pistons are often corroded and can not be reused. Most steel pistons are nickel and chrome plated to resist corrosion, so pistons should never be sanded to clean them up. Doing so removes the protective coating and encourages corrosion.

Q. Is it possible to replace one type of piston with another?

A. Anything is possible, but is it a good idea? Most rebuilders use the same type of piston as the original equipment manufacturer. If a caliper came with steel pistons, it usually gets new steel pistons when its rebuilt. If it came with phenolic pistons, the pistons are usually cleaned and reused or replaced as needed.

In some applications, the OEM has changed piston materials to address certain problems. At one time, Ford used aluminum caliper pistons in F250 pickup trucks. Ford discovered the aluminum pistons were conducting too much heat to the brake fluid which increased the risk of fluid boil and brake failure. So they switched to phenolic pistons to reduce the transfer of heat from the pads to the brake fluid. The change reduced the fluid temperature over 100 degrees during hard use.

Q. Whats the difference between a floating caliper and fixed caliper?

A. One moves and the other one does not. A floating caliper moves in and out on bushings or slides when the brakes are applied. Most floating calipers have a single piston behind the inner brake pad. When the brakes are applied, the piston moves outward and pushes the inner pad against the rotor. It keeps pushing until the caliper slides inward and pulls the outer pad against the rotor. When the brakes are released, the piston retracts allowing the inner and outer pads to bump back away from the rotor. This causes the caliper to recenter itself over the rotor until the next time the brakes are applied.

With fixed calipers, multiple pistons are used to push both the inner and outer pads against the rotor. There are pistons on both sides of the rotor, and the caliper itself is mounted rigidly and does not slide in or out when the brakes are applied. The inner and outer pistons do all the work and squeeze the pads against the rotor.

One of the drawbacks of floating calipers is that they can stick on their slides or bushings if these parts become worn or badly corroded. If the caliper cant slide, the outer pad may never make good contact with the rotor when the brakes are applied. This results in accelerated wear on the inner pad as well as reduced braking effectiveness.

Keeping the bushings and slides lubricated with a high-temperature, moly-based brake lubricant can minimize the risk of sticking with floating calipers. Ordinary chassis grease should never be used for this purpose.

Q. What are anti-rattle clips?

A. Some calipers have small springs or clips that go behind the pads to help prevent vibrations and noise. Shims may also be used behind the pads to further dampen noise.

When the pads are replaced, the anti-rattle clips should be reused (or replace if broken, missing or damaged) to help keep the brakes quiet. If these parts are left off, discarded or forgotten, the brakes may be noisy.


Spark Plugs

Q. Platinum spark plugs and iridium spark plugs - whats the difference?

A. Both are premium spark plugs that have electrodes made of wear-resistant precious metals to extend plug life and improve ignition reliability.

Platinum plugs come in several different configurations. Some have a small wire-like center electrode made of pure platinum, while others have a conventional center electrode made of regular alloy with a small platinum plug welded on the end (single platinum), or platinum plugs welded on both the center and ground electrodes (double platinum). Platinum plugs with the small, pure platinum center electrode may have one, two or four ground electrodes. The use of multiple electrodes reduces misfires and electrode wear.

Iridium plugs, by comparison, use an iridium/rhodium alloy for the center electrode. The center electrode is very thin (0.4 to 0.7 mm depending on the type of plug and the application), and there is usually only a single ground electrode.

As for the metals themselves, platinum and iridium are both good conductors of heat and electricity, and resist wear and corrosion. Both platinum and iridium are hard, strong metals that have high melting temperatures.

Q. What kind of spark plugs are required to meet OEM 100,000-mile service intervals?

A. Platinum or iridium long-life plugs. Standard spark plugs dont have the wear resistance of plugs with platinum or iridium electrodes.

With standard nickel-alloy electrodes, the spark gap between the center and ground electrodes grows about .0002 to .0006 inches for every 1,000 miles of driving. After 45,000 miles of driving, the gap can grow as much as 0.015 inches or more. This increases the risk of ignition misfire, so the plugs need to be changed.

To reduce maintenance, most vehicle manufacturers use some type of long-life, 100,000-mile spark plug. The brand and type of plugs a vehicle manufacturer uses in a particular engine depends on who the main supplier is for spark plugs. That doesnt mean another brand or type of spark plug wont work.

Replacement spark plugs can be the same brand and type as the original plugs, or they can be another brand or type - provided there is a plug available to fit the application (usually there is).

Consequently, you can sell any brand or type of long-life platinum or iridium replacement spark plugs for later-model vehicles that were originally equipped with 100,000-mile plugs. And you can also recommend either type of long-life plug as an upgrade for older vehicles that were originally equipped with standard spark plugs.

Premium spark plugs only cost a little more than standard plugs and provide longer life and improved ignition reliability.

Q. Can the shape or configuration of the electrodes on a spark plug reduce the risk of misfire and/or improve performance?

A. Yes. Spark plug manufacturers make a variety of different electrode designs for various reasons.

Most traditional spark plugs have a J-gap ground electrode. The electrode is so-named because of its appearance. The ground electrode protrudes from the plug shell and is bent over so the end is directly over the center electrode. For normal driving, this provides a good combination of longevity and fouling resistance. But it also shrouds the spark and increases the risk of misfire with lean fuel mixtures and high-rpm engine operation.

One of the tricks racers have long used is to cut back the outer electrode to the tip ends next to the center electrode rather than over it. This opens up the spark and reduces the risk of misfire. But it also drastically shortens plug life. For a race car, its not an issue if the plug only goes 500 miles. But street-driven vehicles need plugs that will go 50,000 to 100,000 miles.

Many racing plugs use an A-gap design. Its essentially the same cut-down ground electrode configuration except that instead of modifying a stock J-gap plug, it is made by using a shorter electrode and attaching it to the shell at a slight angle. The shorter electrode also means there is less heat buildup in it, which reduces the risk of pre-ignition when the engine is running hard.

Most NASCAR teams use spark plugs with four A-gap ground electrodes spaced every 90 degrees around the center electrode. Adding extra electrodes does not create multiple sparks when the plug fires, but it does give the spark more choices from which to choose. This reduces the risk of misfire and helps the plugs go the distance because wear is spread across four electrodes instead of just one.

One new spark plug design features a diamond-shaped open architecture electrode. An engineer from the company said that their design forces air gap discharges, creates an edge-to-edge spark path, allows free replenishment of the spark zone wth a fresh fuel/air change and exposes the flame front more directly to the piston head.

Other types of performance plugs for high-performance and racing include plugs with fluted center electrodes, plugs with a V-shaped ground electrode and plugs with surface gap electrodes.

The basic objective of most special electrode configurations is to make it as easy as possible for the plug to fire reliably. A spark jumps more easily from a sharp edge than a rounded blunt edge. So the more sharp edges it has to jump to, the better the odds of the plug firing under all types of driving conditions.

Special electrodes may also be shaped in such a way that they help unshroud the spark so that more of the spark will be exposed to the air/fuel mixture. This improves the propagation of the flame kernel once the fire is lit.

Q: Do 100,000-mile spark plugs really last 100,000 miles?

A: Under ideal conditons, yes. Long life spark plugs, such as those with exotic metals in them (platinum and iridium) are fully capable of lasting for a full 100,000 miles because these metals can eliminate electrode wear. But long-life plugs are not foul-proof if the engine is not running properly.

If, for example, the valve or value guide seals become worn over time, the engine can start to use oil and may experience premature plug fouling.

Such problems may occur far short of the 100,000 mile mark. Additionally, fuel delivery problemscaused by dirty injectors or sensor malfunctions somewhere in the system can upset the fuel mixture and contribute to fouling. Thats why its sometimes necessary to replace 100,000-mile, long-life spark plugs long before they reach the 100,000 mile mark.


Suspension & Chassis

Q. How often should shocks and struts be replaced?

A. It depends on the vehicle application, the mileage, the kind of driving the vehicle has been subjected to and the condition of the original shocks and struts.

Driving on rough roads with potholes, bumps and ruts can be hard on the suspension and dampers. The constant pounding accelerates wear and shortens the service life of shocks, struts, tie rod ends, ball joints, control arm bushings and even springs. The suspension and ride-control system are designed to withstand this kind of abuse under normal driving conditions, but unusually heavy loads, extremely rough driving conditions and driving in extremely dusty, wet or corrosive environments will obviously speed up the rate at which suspension and ride control parts wear out.

One shock manufacturer recommends replacing shocks and struts every 50,000 miles, but its hard to pick an arbitrary number out of the air thats right for every application. For the average vehicle under average driving conditions, 50,000 miles may be a reasonable benchmark for checking and/or replacing shocks and struts. It all depends on the condition of these parts.

Many motorists do not notice the gradual wear that has occurred in their ride-control systems because it occurs slowly over time. But after four, five or six years of driving, there is often a noticeable difference in the way the vehicle rides and handles now compared to how it handled and rode when it was new.

The safety aspect of ride control is often overlooked as a selling point for replacing worn shocks and struts. Yet it is a very important point to emphasize because the dampers help maintain traction on rough roads by keeping the tires in contact with the road. If the suspension is bouncing all over the place, the tires will be hopping and skipping and losing their grip. This hurts steering stability, handling agility and braking. Tests have shown that a vehicle with worn shocks requires a significantly longer distance to stop on a rough road than a vehicle with good shocks. The difference in stopping distance is typically greatest on vehicles with high centers of gravity like many of todays SUVs. That margin might make the difference between avoiding an accident and being involved in one.

Sometimes a customer will want to replace his original equipment shocks or struts with aftermarket performance shocks or struts. In this kind of situation, the mileage on the parts is irrelevant because the customer is making a ride-control upgrade. Hes not replacing worn parts. The selling opportunities here are almost unlimited because there are a wide variety of aftermarket shocks and struts from which to choose.

Q. Whats so great about gas shocks?

A. They dont fade like ordinary shocks. When the piston inside an ordinary shock strokes up and down, it churns the fluid and forces it through small orifices. This creates resistance that dampens the motions of the suspension to provide the desired amount of ride control. But when the piston pumps faster and faster on a rough road, it tends to aerate the fluid and turn it into foam. Bubbles do not create the same resistance as a liquid, so the shock fades and offers less resistance than before. This softens up the suspension, allows more wheel bounce and body roll and generally hurts handling performance.

Adding a charge of high-pressure nitrogen gas to the fluid reservoir inside the shock puts the fluid under pressure. This helps prevent the formation of bubbles when the piston is working hard, so there is much less fade, and the shock remains firm.

There are high-pressure (up to 350 psi or higher) gas-charged shocks and struts, which are typically a monotube design with a floating piston that separates the gas charge from the fluid, and lower-pressure (70 to 250 psi depending on the application) gas-charged conventional twin-tube shocks. The high-pressure dampers are often preferred for all-out handling performance because of their greater fade resistance.

Q. What is the number-one cause of tire wear?

A. Misalignment, which is often caused by worn, damaged or bent suspension parts. The most common culprits are worn tie rod ends, but bent tie rods, bent steering arms, worn control-arm bushings, ball joints and weak springs can all be contributing factors.

When an alignment technician checks the alignment on a vehicle, he is supposed to do a pre-alignment inspection of the steering and suspension systems and measure ride height to check for spring sag. Unfortunately, too many technicians skip this important step and just hurry through the alignment so they can get on to the next job. Consequently, they miss a lot of steering and suspension parts that need to be replaced.

The consequences of not replacing worn or damaged steering or suspension parts can be a lot more serious than toe or camber wear on the tires. If a worn tie rod end pulls apart, the driver may lose steering control of his vehicle. The same can happen if a worn ball joint separates and allows the suspension to collapse.

Steering and suspension parts should be inspected any time a vehicle is experiencing a steering or handling problem such as suspension noise, a drift or pull to one side, instability or steering wander, or looseness in the steering. Any parts that are worn, damaged or out of specifications should be replaced without delay.

Q. What are low-friction steering and suspension parts?

A. They are joints designed to offer less turning resistance than traditional steel bushing joints. When ball joints first appeared back in the 1950s, they were a significant improvement over king pin suspensions. Cars at that time were much heavier than today, so it didnt matter much if the ball joints created a certain amount of resistance.

In the early 1980s, European vehicle manufacturers began using a new type of joint design that offered much less resistance. The low-friction ball joints and tie rod ends reduced steering effort and improved steering return on vehicles equipped with rack and pinion steering and MacPherson struts. The domestic vehicle manufacturers saw the advantages of the new joint design and also began using them on front-wheel-drive cars. Today, almost all front-wheel-drive cars have low-friction joints, as do many later-model trucks.

Ford pickup trucks with Twin I-Beam suspensions were among the earliest low-friction truck applications. The new joints greatly improved steering return. Chevrolet went to low-friction ball joints in 1988. Dodge made the switch in 94 when it introduced its redesigned Ram pickup. In 97, Dodge used the joints on the new Dakota pickup.

The low-friction joint reduces turning friction by using a highly polished (near mirror finish) on the ball. The ball is supported by a tough polymer bearing (typically Delrin, which is a DuPont polymer similar to Kevlar). A tight-fitting, long-life seal completes the assembly to keep contaminants out and lubricants in. Therefore, most low-friction joints do not have grease fittings and are sealed for life. But some of the earlier hybrid designs do have grease fittings, as do most steel joints with steel bearings.

On applications where the original ball joints, tie rod ends, tie rod sockets and idler arms are a low-friction design, the same type of replacement joint should be installed to maintain the same steering effort, return and feel.


Timing Components

Q. Is it still necessary to replace timing belts on newer vehicles?

A. Yes. Timing belt replacement is one service that isnt going away any time soon. Most engines with overhead cam timing belts still have a recommended replacement interval.

For newer vehicles, the interval is typically 100,000 to 120,000 miles depending on the application. For most vehicles with OHC engines that were manufactured prior to 1997, the recommended replacement interval is usually 60,000 miles.

Its also important to stress to customers that timing belts need to be replaced as a maintenance item, rather than as a repair. At best, a broken timing belt will leave a motorist stranded. At worst, the motorist will be stranded and will face a very big repair bill. This is especially true with so-called interference engines. These motors do not have enough clearance between the valves and pistons to prevent contact and damage if a timing belt fails.

Q. Whats the reason for replacing timing belts?

A. The timing belt in an overhead-cam engine drives the camshaft(s), which in turn opens and closes the valves. As the belt ages, it weakens. The rubber on the outside of the belt can harden and crack. The reinforcing cords inside the belt that provide tensile strength and prevent the belt from stretching can also lose strength. The laminated layers of the belt may also beginning to separate.

After 60,000 or more miles of continuous use, the timing belt may be on the verge of failure. Dont go by looks alone. Many belts with a lot of miles on them still look good as new on the outside. Even so, thats no guarantee the belt is still in good condition on the inside. So if a customer is driving a vehicle that is more than five or six years old, he may be driving on borrowed time if the timing belt has never been replaced. The risk of belt failure goes up sharply once the belt surpasses its recommended replacement interval.

Unfortunately, there is usually no noise or other symptoms to warn a motorist that the timing belt has reached the end of the road. One minute the engine is running fine, and the next it has failed. The only sound the motorists hears is the frustrating wheezes from an engine that cranks but wont start because it has no compression.

Worse yet, if their car has an interference engine (one that lacks enough clearance between the valves and pistons to freewheel should the timing belt break), the engine wont even crank because the valves will be right against the pistons. This can cause very expensive engine damage and will certainly cost a lot more to repair than what it would have cost to replace the belt and components.

Any timing belt that shows obvious damage such as frayed or exposed cords, damaged teeth, hunks of rubber missing, deep cracks, excessive surface cracking or severe glazing should be replaced without delay. Small surface cracks on the ribbing is considered normal, but extensive cracking or deep cracks are not.

If a belt has stripped cogs, something in the cam drive system has jammed or stuck, overloading the belt and causing it to shear teeth or jump time. The most likely culprit is the camshaft, which may have seized due to engine overheating or lack of lubrication (low oil level or loss of oil pressure).

Q. Should any other parts be replaced along with the timing belt?

A. Yes. It doesnt make much sense for your customer to replace only the timing belt. In fact, research indicates that a new belt will last only half of its expected lifespan if the timing components are not replaced at the same time as the belt. Nevertheless, statistics show that only about half of technicians replace the belt and hardware when doing a timing job. Its best to do the complete job, and that means replacing all of the components at the same time.

While the timing belt is being replaced, there are other components that should be replaced at the same time. These components can be found separately, or a better option is to sell your customer a timing component kit that includes all of the needed timing parts.

The tensioner, springs, idler pulley and possibly even the water pump should be replaced on most engines. Tensioner and idler pulley bearings are sealed for life and are not serviceable. So theres no way to clean, inspect or relubricate the bearings when the belt is changed. Over time, the grease inside the bearings breaks down and oxidizes, accelerating bearing wear and increasing the risk of a bearing failure or seizure. And the hotter the operating environment, the shorter the lifespan of the grease and the bearings. The location of the tensioner and idler pulley under the timing belt cover prevents them from receiving much cooling, so they tend to run quite hot.

When a tensioner or idler bearing seal fails, dirt and humidity enter the bearing and grease leaks out. The bearing is doomed and will eventually fail. The first symptom is usually noise. If ignored long enough, the next symptom may be jumped timing as the belt loses tension, or belt failure.

Many timing belt kits include most of the components needed to do a complete timing job. These kits include the tensioner, idlers and springs. If these parts are not included, look them up and recommend them to your customer when he is buying a belt.

As for the water pump, it is often located behind the timing belt. The lifespan of the water pump is about the same as the timing belt, so replacing both at the same time can save the labor of having to tear everything apart twice.

Q. Does a replacement timing belt have to be the same as the original?

A. Absolutely! Belt length, width, tooth profile and pitch must all be exactly the same as the original, and the material must be the same or better.

Do not substitute a less expensive neoprene belt for one made of HSN (Highly Saturated Nitrile). Some no-name brands use inferior materials that wont last as long as the OEM belt or a quality aftermarket belt.















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