Antilock Brake System

Antilock Brake System

Antilock brake systems have been around since the mid-1980s and are now offered as standard equipment or as an option on most vehicle makes and models.

There are a lot of ABS-equipped vehicles on the road today that will eventually need ABS replacement parts as they age.

What kind of parts fail? Wheel speed sensors are probably the most often replaced component. Most wheel speed sensors (WSS) are located at the wheels, which makes them vulnerable to road splash, corrosion and road hazards. The WSS wires and connectors are also often a source of trouble.

On many vehicles, each wheel has its own speed sensor. These are called "four channel" ABS systems. On others, a common sensor is used for the rear wheels (which may be mounted in the differential or transmission) but each front wheel still has its own wheel speed sensor. These are called "three-channel" ABS systems.

Another variation is the "single-channel" rear-wheel-only ABS system that is used on many rear-wheel-drive pickups and vans. This includes Ford "Rear Antilock Brakes" (RABS) and GM and Dodge "Rear-Wheel Anti-Lock" (RWAL). The front wheels on these trucks have no speed sensors and only a single speed sensor mounted in the differential or transmission for both rear wheels. Rear-wheel antilock systems are typically used on applications where vehicle loading can affect rear wheel traction, which is why it’s used on pickup trucks and vans.

Most ABS systems use magnetic wheel speed sensors that generate a frequency signal as the notches on the sensor ring pass by the tip of the sensor. The sensor ring is usually mounted on the back of the brake rotor or outer CV joint.

On some vehicles (many GM models, for example), the wheel speed sensor is built into the sealed wheel hub assembly – making it very expensive to replace if it fails because the entire hub has to be changed. On most vehicles, though, the wheel speed sensor can be replaced separately if it fails.

The WSS signal is sent to the ABS control module, where the signal pulses are counted so the module can monitor wheel speed. If the tip of the WSS becomes coated with debris, or there’s a poor wiring connection between the sensor and module, or the "air gap" between the end of the sensor and the sensor ring is too large, it may prevent the WSS from generating a good signal. An internal short or open in the sensor itself can also render it useless. The ABS control module will detect the problem and set a fault code that identifies the "bad" WSS circuit (a number that corresponds to left front, for example.) This does not mean the sensor itself is bad, only that there is a signal problem in that WSS circuit.

The troublesome WSS circuit can be diagnosed by measuring the resistance of the WSS with an ohmmeter, by checking wiring continuity and inspecting the wiring and connectors, or by spinning the wheel and checking the sensor’s output signal.

If a WSS sensor is lost, the ABS system can’t monitor wheel speed and can’t tell if ABS is needed or not. So it will set a code and disable itself. As long as the warning light remains on, the ABS system will stay "off line." Only when the fault has been fixed and the code cleared will the warning light go out, allowing the ABS system to become active again.

ABS systems are designed to be as "fail-safe" as possible. All ABS systems run their own self-diagnostics and will set codes and deactivate themselves when a serious fault is detected. An illuminated ABS warning light may seem ominous, but most vehicles should still be safe to drive and have normal braking. The only exceptions are some older vehicles with "integral" ABS systems that use the ABS pump and accumulator to provide power-assisted braking. On these vehicles, the brakes should still work, but without the benefit of any power assist if the ABS system goes down.

If the brake warning light is also on, however, it may indicate a more serious problem such as loss of brake fluid or a low fluid level. So if both warning lights are on (ABS and brakes), the vehicle should not be driven until the problem can be investigated.

Another ABS component that often fails is the hydraulic modulator assembly that contains the ABS solenoid valves, or in the case of GM ABS-IV systems, the motor pack and valve assembly. This is the heart of the ABS system that controls the cycling of hydraulic pressure to the wheels. On some systems, the ABS solenoid valves can be replaced separately if one fails.

But on many systems, the entire modulator must be replaced if anything inside fails. Failures may be caused by electrical faults (opens or shorts in solenoids), by internal corrosion or by debris in the brake fluid that jams a solenoid valve or prevents it from fully closing.

Modulators can be tricky to replace because they must be bled after they have been installed to remove all air from the circuits. On some vehicles, they may require using a scan tool to cycle the ABS solenoids. On others, manual bleeder screws may be provided for this purpose. Either way, your customer will also need brake fluid to refill the system. The old fluid should also be flushed out to get rid of any sediment or contamination that may cause future problems.

On systems that use a high-pressure pump and accumulator to provide power-assisted braking or to reapply pressure during an ABS stop, a defective pump or relay can cause a loss of pressure. So can a leaky accumulator. The ABS system monitors these components and will set a code if it detects a problem.

The accumulator can be dangerous to replace because it may contain up to 1,500 or more pounds of pressure. Your customers should be warned to never open up an ABS system that may still be under pressure. The accumulator must first be discharged by pumping the brake pedal 40 times with the ignition key off. Once all pressure has been relieved, it can be safety removed and replaced.

ABS control modules can also fail, though they don’t fail that often. Most ABS problems are electrical (bad WSS, pump relay, pump motor, wiring or solenoid) or mechanical (sticking, jammed or leaking ABS valve.) If a module does go bad, it may cause erratic or abnormal operation of the system (such as ABS braking during a normal stop.) ABS should only come into play when traction conditions are marginal or during sudden "panic" stops. The rest of the time, it should have no effect on normal driving or braking.

When ABS comes into play, the module energizes the solenoid valves in the hydraulic modulator to hold, release and reapply hydraulic pressure to the brakes. Sealing off the affected brake circuit prevents any additional pressure from being applied to the brake. The module then energizes a vent solenoid to release pressure from the line. This allows the brake to release momentarily so the tire can regain its grip. The vent valve is then closed and the pressure valve reopened to reapply the brake. This rapid cycling produces a pulsating effect that can usually be felt in the brake pedal during an ABS stop. The driver may also hear a buzzing or chattering noise from the ABS hydraulic unit – which is normal and tells the driver that the ABS system is active.

 


 

BATTERIES

The battery is a storehouse of electrical energy.

The battery supplies amps to crank the engine, voltage to keep all of the onboard electronics alive even when the ignition is off, and extra juice to meet the vehicle’s electrical demands when the alternator can’t keep up.

The battery’s ability to maintain a certain voltage level is critical in today’s vehicles. Low voltage can upset the normal operation of many onboard electronics and cause all kinds of problems from hard starting to stalling to erratic performance. That’s why a fully-charged battery in good condition is a must for reliable driving.

A 12-volt battery has six "cells," each of which may contain nine to 20 positive and negative plates (typically the greater the number of plates, the greater the amperage capacity of the battery.) Each cell produces 2.11 volts, so when all six cells are connected together in series, the battery’s total output is actually 12.66 volts.

One thing all batteries share in common is that they don’t last forever. Four to five years is the average life of most batteries. Life is limited because the chemical processes that make a battery work prove to be its undoing. The chemical reactions that occur between the sulfuric acid in the battery and the lead in the battery’s cell plates gradually damages the plates. Over time, some of the sulfate sticks to the plates and doesn’t return to solution when the alternator pumps current back through the battery. The plates become "sulfated" and lose some of their ability to hold a charge. As the sulfate builds up, it forms a barrier that further diminishes the battery’s ability to produce and store electricity. Eventually the point is reached where the battery will no longer accept a charge and the battery must be replaced.

Battery plates can also become "sulfated" prematurely if the battery is run down repeatedly (leaving the lights on, playing a killer stereo system without the engine running, etc.) or if the battery is chronically undercharged (frequent short-trip driving, especially during cold weather.)

Premature battery failure can also be caused by excessive heat (as in Arizona summers) and vibration. The lead alloys that are used in maintenance-free batteries are fairly brittle and can’t take much abuse. Rough handling or a missing hold-down strap that allows the battery to flop around on its tray can result in cracked or shorted cell connections and instant battery failure.

The Battery Manufacturers Association says probably 50 to 60 percent of the batteries that end up in the scrap heap for recycling are still usable but have been discarded because they won’t accept a charge. Sometimes a "dead" battery can be revived by applying a long slow trickle charge, by connecting it in parallel (positive to positive, negative to negative) with a good battery and charging both at the same time, or by using a special battery charger that applies a higher-than-normal initial charging voltage to break through the sulfate. But by the time a battery is four or five years old, it’s days are numbered, and sooner or later it will have to be replaced.

When a customer needs a new battery, your first job is to figure out the correct "group size" based on the year, make and model of the vehicle. You can also use the group size of the old battery.

A replacement battery must be a compatible group size with similar height, width, length and post configuration as the original. This is necessary so it will fit the battery tray and holddowns. Also, it must have the same or higher cold cranking amp (CCA) capacity as the original. For most vehicles, that means a minimum of 450 to 600 CCAs. The bigger the engine, the more amps it needs for reliable cold weather starting.

The next decision that has to be made is what type of battery best suits your customer’s needs: a conventional battery with liquid electrolyte or a gel battery? The acid in gel batteries is held by absorbent glass mats between the cell plates. Gel-type batteries are spill-proof and are well suited for hot climates (less risk of evaporation.) They are also more resistant to vibration-damage.

Some gel batteries have round cells with spiral-wound plates instead of the more conventional flat cell plates. This increases the internal surface area of each cell up to 20 times per amp hour and creates a current path that is 20 to 100 times shorter than conventional flat plate batteries. This allows the battery case to be up to 40 percent smaller and lighter than a traditional battery, to produce up to 25 percent more cranking amps and to recharge four times faster than other batteries.

One thing that should always be checked when replacing a battery is its sate of charge. Most batteries are dry charged (precharged) at the factory for maximum shelf life. Even so, customers should be advised to put a charger on the battery to bring it up to full charge before it is installed in a vehicle. This will reduce the risk of overtaxing the charging system should the battery be low.

The vehicle’s charging system should also be checked to make sure it is putting out adequate amperage and voltage to keep the new battery fully charged. The charging voltage is usually about 1-1/2 to 2 volts higher than normal battery voltage.

When batteries are sold, sell the oldest ones first to keep your stock fresh. All batteries have a date code that reveals when the battery was manufactured. The number indicates the year, and the letter corresponds to the month (A = January, B = February, C = March, etc.) The date code can also be used to determine the age of a battery in a vehicle if the age is unknown or unmarked.

Your customer will also have to decide how much warranty he wants to buy. Replacement batteries all come with some type of warranty, be it 24, 36, 48, 60, 72 or more months. As a rule, the longer the warranty, the better the battery – but the higher the price. Most warranties are pro-rated which means a certain amount is deducted for each month the battery has been in service.

 


 

BELTS & HOSES

All vehicles need replacement belts and hoses at some point in their life. The question is when?

Synthetic rubber provides flexibility for these components, but over time exposure to heat and chemical attack causes the rubber to degenerate, lose strength and become stiff and brittle. That’s why all belts and hoses eventually have to be replaced.

Most motorists never even think of replacing their belts or hoses – until one fails, and even then they only replace the one that failed. And so it goes until the next one fails, and the next one and the next one.

Most belt and hose manufacturers recommend replacing belts and hoses every four to five years because they know these parts don’t last forever. Sure, many belts and hoses go six, seven or even 10 years without a problem. But many don’t, and when a belt or hose fails, it almost always leaves the motorist stranded.

The reason not to wait until a belt or hose fails to replace it is to reduce the risk of a breakdown. Think of new belts and hoses as longevity insurance for the engine’s cooling and charging system – and maybe the engine too.

If a belt fails, it can cause the loss of engine cooling, power steering, charging and air conditioning (depending on what it drives.) With single-belt serpentine drive systems, one belt does it all. With V-belts, there may be separate or shared belts for the engine’s accessories (water pump, power steering pump, A/C compressor and alternator.)

It’s the same story with hoses, but more so. A radiator or heater hose that springs a leak will soon spray the engine’s vital supply of coolant on the ground. Depending on how bad the leak is, the first indication of trouble may be a rising temperature gauge, a temperature warning light or a cloud of steam billowing out from under the hood. If the vehicle is not shut off almost immediately, the engine may get too hot and suffer damage to the head gasket, cylinder head, valve guides and/or pistons and cylinders. The price of replacement hoses will seem cheap compared to what it costs to fix this kind of engine damage should it occur.

Heat is the number-one enemy of belts, especially V-belts. If a V-belt isn’t tight and slips, friction between the sides of the belt and pulley generate heat and noise (belt squeal.) This can glaze and harden the sides of the V-belt and cause it to lose its grip, which results in more slippage, accelerated belt wear and premature belt failure. Any V-belt that is glazed, cracked or frayed, therefore, should be replaced regardless of its age.

Belt tension is critical with both serpentine belts, flat belts and V-belts, and it must be adjusted properly and maintained for good belt performance, quiet operation and long life. Most engines with serpentine belts have a spring-loaded automatic tensioner that eliminates the need for an initial adjustment as well as readjustments. But on applications that don’t have an automatic adjuster, belt tension must be adjusted to specifications, then readjusted after a short break-in period.

Belts should be inspected regularly for obvious signs of wear or damage. Minor surface cracking is normal, but heavy or deep cracking, fraying, missing chunks of rubber or other damage are warning signs the belt has reached the end of its service life and needs to be replaced. Hard, shiny spots (glazing) would also be a reason for replacement as would noise. Glazing and noise can also be caused by pulley misalignment, so pulleys should be inspected to make sure they are properly aligned (especially if an engine is throwing, twisting or eating belts.)

REPLACEMENT BELTS

When looking up a replacement belt for a customer, you may need quite a bit of information to find the correct one. In addition to year, make, model and engine size, you may also have to know if the engine is equipped with air conditioning, power steering and/or an air pump. On some applications, you may also need the VIN number to accurately identify the application.

It’s always a good idea to compare a replacement belt with the old one to make sure they are the same width and length. A replacement V-belt that’s too narrow may bottom out in a pulley and slip, while one that’s too wide may not fit the grooves in the pulley. The length of a replacement V-belt or flat belt can vary a little depending on the amount of adjustment that’s possible. But on serpentine belts, the replacement belt must be the same as the original because most automatic tensioners have a limited range of travel. A difference of only an inch or so may be too much for some applications.

There is no recommended replacement interval for automatic belt tensioners, but that doesn’t mean these units will last forever. Like any mechanical component, they eventually wear out. Replacement becomes necessary when the unit is no longer able to maintain proper belt tension or the unit is making noise. Symptoms of a bad tensioner include clatter, rumble or chirp when the engine is running, visible looseness in the idle pulley bearings, dragging or seized idler pulley bearings (the pulley should rotate freely), physical damage to the idler pulley wheel, arm or base housing, or belt squeal immediately after engine start up or when belt-driven accessories are under load.

As for hoses, any hose that is leaking, cracked, blistered, swelling or shows signs of damage needs to be replaced. Hoses routed near exhaust manifolds or near sharp objects may rub and chaff leading to hose failure. Hoses that have become hard and brittle are also overdue for replacement.

Cooling system hoses often fail from the inside out due to electrolytic corrosion. Some hoses are more vulnerable than others to this type of problem depending on the materials used in their construction. Coolant neglect may be an underlying cause of such hose failures. In some instances, a missing or loose ground strap between the engine and chassis can force electrical current to use the coolant as a path to ground increasing the risk of electrolytic attack on the inside of the radiator hoses.

Replacement radiator hoses may be molded (preshaped the same as the original hose) or universal flex hose (consolidates applications.) The important things to match here are hose diameter and length. (New clamps should also be recommended.) And don’t forget to offer your customer a chance to purchase antifreeze.

 


 

BRAKE CALIPERS

The calipers on disc brakes squeeze the pads against the rotors when the brakes are applied.

It’s a simple job but one that can’t tolerate any fluid leaks, sticking or jamming.

If a caliper sticks, it may cause the pads to wear unevenly or the brakes to drag. That’s why the calipers must be carefully inspected when the brakes are relined, rebuilt or replaced if there’s a problem.

Loaded calipers are a popular replacement alternative to bare calipers. But their popularity varies from one area of the country to another. According to one brake supplier, loaded calipers are much more popular on the West Coast of the U.S. than on the East Coast. The reason? West coast technicians like loaded calipers because everything they need comes in one box; they don’t have to worry about mismatched parts from different suppliers, the complete assemblies are quick and easy to install and they see fewer comebacks because of brake noise or other problems. East Coast technicians also like loaded calipers for the same reasons, but do business in a market that is much more sensitive to price. Consequently, the Easterners typically reuse more parts and replace calipers only when necessary.

Regardless of which part of the country you live in, loaded calipers do provide a variety of benefits when doing brake jobs. Most brake suppliers have a loaded caliper program, so availability is seldom an issue. Price, though, remains the main selling hurdle to overcome.

One of the main advantages for the vehicle owner is that loaded caliper assemblies help restore the brakes to like-new condition. Not only do they get new friction, but also a professionally rebuilt caliper and properly matched hardware (shims, bushings, slides, etc.) This significantly reduces the risk of future leaks developing and uneven braking or pad wear caused by calipers hanging up or dragging.

Caliper piston seals don’t last forever, and once they start to leak, it’s the end of the road for the caliper and the pads. Fluid leaks are dangerous because they can lead to a loss of hydraulic pressure in the brake circuit that may cause the brakes to fail. Brake fluid leaking from a caliper can also contaminate the brake linings and cause them to grab or pull.

A caliper may also have to be replaced if it’s sticking. Internal corrosion can cause pistons to jam or freeze preventing the caliper from working normally or releasing completely. External corrosion on the caliper mounts, bushings or slides can cause problems too by preventing a floating caliper from moving normally when the brakes are applied. The result here may be uneven pad wear, uneven braking, dragging or a pull. With a loaded caliper, the caliper is replaced along with the pads.

Attempting to rebuild old calipers is often a waste of time. In many instances, the calipers are so badly corroded or worn, they can’t be rebuilt – or they leak when they are put back on the vehicle. Disassembling a caliper to replace the piston seal and dust boot is a messy job, and it may be difficult or impossible if the piston is stuck in place. Steel pistons often can’t be reused because they’re usually too badly corroded, and scratches or pits in the caliper bore may cause the caliper to leak even after a new piston and seal are installed. That’s why most technicians prefer to replace old calipers with remanufactured ones.

Replacing the hardware is also important because old corroded hardware can cause braking problems. We’ve heard of shims that have worked loose and caused a rotor to fail by rubbing and cutting through the rotor hat! If a technician forgets to install an anti-rattle clip, or installs one that doesn’t fit properly, the newly installed pads may be noisy. Loaded calipers reduce these risks by providing the proper hardware and replacing everything that should be replaced.

The type of friction material that’s included with a loaded caliper assembly is critical because it should be the same or better than the original. If a vehicle originally had ceramic pads, the loaded caliper should have the same type of friction material. The same goes for semi-metallic pads.

To avoid a mismatch of friction side-to-side, both calipers should be replaced simultaneously if you’re installing loaded calipers. If only one caliper is being replaced, be sure to sell the same friction pads for both sides.

When a loaded caliper is installed, the brake system should always be flushed and refilled with clean, fresh fluid that meets the OEM requirements for the application.

Caliper slides and bushings should be lubricated with a high-temperature brake grease, and related brake components such as hoses, lines, rear wheel cylinders and the master cylinder should all be inspected to make sure these components are in good working condition and are leak-free.

 


 

CHASSIS & RIDE CONTROL

Chassis parts carry a lot of weight and play a prominent role in maintaining wheel alignment, handling, steering stability, traction and driving safety.

Chassis parts are out-of-sight, out-of-mind, and are often overlooked as a profit opportunity for your store.

Most chassis parts are kept behind the counter because they are generally a slow-moving product line compared to many other items. Consequently, you won’t see many chassis parts on display except maybe some performance suspension parts such as handling kits, brightly colored sway bar bushings or coil-over kits for sport compact cars, or overload springs or lift kits for trucks.

Chassis parts inventories that are in stock are also limited to only the most common parts. Why? Because ball joints, control arm bushings and springs are long lived and may only be replaced once during a vehicle’s life – if at all. Many vehicles reach the end of the road with many of their original chassis parts still in place. That doesn’t mean those parts went the distance. Many were probably worn out and should have been replaced – but nobody ever noticed or told the vehicle owner that repairs were needed.

Unless a vehicle owner is making changes to the suspension to upgrade handling or towing/hauling capacity, or wants to change the ground clearance of the vehicle (raised for off-roading or lowered for handling and aerodynamics), chassis parts are seldom touched unless they are worn out or damaged and need to be replaced. Many drivers do not notice the gradual deterioration in ride, handling and steering that occurs over time.

Consequently, they may not realize their ball joints or springs or tie rod ends are worn out until things are really bad or something actually fails causing the suspension to collapse or loss of steering control.

Most worn suspension parts and steering components are discovered when a vehicle is in for other types of service work, such as a brake job, oil change or alignment.

A vehicle cannot maintain proper wheel alignment with worn chassis parts. Worn ball joints can upset camber/caster alignment causing uneven tire wear, pulling and suspension noise. Worn control arm bushings can also affect camber/caster alignment and cause unwanted noise. Worn tie rod ends upset toe alignment and cause rapid tire wear. A worn idler arm can cause steering wander and tire wear too. Even spring sag can upset alignment and have an adverse effect on steering, handling, ride quality and tire wear. That’s why alignment technicians always inspect the steering and suspension before they do an alignment. If worn or damaged parts are found, they must be replaced before the wheels can be aligned to specifications.

Sometimes a motorist will ask for an alignment if his or her vehicle is wearing tires unusually fast or pulling to one side. Most tire dealers recommend an alignment check when tires are replaced because accurate alignment assures maximum tread life and the best possible handling. But many people don’t want to spend the money and put off having their alignment checked – until it is too late and their new set of tires have been ruined because of worn chassis parts.

When parts are needed, you obviously need the year, make and model – and sometimes the VIN – to accurately identify the application. But with chassis parts, you also have to know which ball joint or tie rod a customer wants because parts vary depending on their location.

With ball joints, there are upper and lower ball joints on each side if a vehicle has a short arm/long arm (SLA) suspension, but there are only lower ball joints if the front suspension has struts. Left and right ball joints are usually the same, unless they are part of a control arm assembly. The rear suspension may also be equipped with ball joints. A special tool will be needed to separate the ball joint from the steering knuckle, and some ball joints may have to be pressed out of their control arms.

With tie rod ends, there are inner and outer tie rods on vehicles that do not have rack and pinion steering. Most recirculating ball steering systems have a parallel steering linkage with an idler arm opposite the pitman arm that’s connected to the steering box. A center link ties the two sides together. Those with racks have a simpler arrangement with an outer tie rod end on each side and inner tie rod sockets attached to the rack. The inner sockets are covered by rubber or plastic bellows. Left and right side tie rods are almost always different because one is usually has reverse threads to facilitate toe adjustments.

Replacing a chassis part usually alters steering geometry, so realigning the wheels is almost always necessary after the new parts have been installed.

Springs often have to be replaced because of sag or failure. All springs will sag as they age due to metal creep, but some may sag at a faster rate if a vehicle is heavily overloaded or driven on unusually rough roads. Spring sag changes ride height, which in turn changes wheel alignment. If ride height is at or below minimum specifications, new springs are needed. Springs may also break as a result of corrosion or metal fatigue. Many springs are painted or coated with plastic to protect them from the elements. If the coating is scratched, corrosion can attack and weaken the spring.

Springs are usually replaced in pairs. Upgrade options include replacing standard springs with variable-rate springs or overload springs. Both provide increased load-carrying capacity, but variable-rate springs provide a softer ride. Replacing coil springs often requires a spring compressor. Related parts that may also be needed include spring pads that go under the springs, new bearing plates for the tops of MacPherson struts and new fasteners.

 


 

COOLING SYSTEM & ANTIFREEZE

Selling antifreeze these days almost takes a degree in chemistry.

Coolants today come in various colors and formulations. There are "conventional" coolants (the familiar "green" antifreeze that’s typically good for two years or 30,000 miles), and a variety of long-life coolants that may be orange, red or even blue and are usually rated for five years or 150,000 miles. The color really doesn’t mean much because it’s just dye. It’s what in the chemistry of the product that counts.

Some types of coolants are formulated for specific vehicle applications or engine types (such as aluminum engines or bimetal engines with iron blocks and aluminum heads.) Some vehicle manufacturers have very specific preferences when it comes to the types of corrosion inhibitors they use. The North American OEMs like one kind of chemistry, the Asian OEMs like another and the Europeans have their own ideas about what works best. That’s why there’s so much confusion about what kind of antifreeze to use.

The aftermarket, on the other hand, is great at coming up with ways

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