Suspension & Driveline Parts

Suspension & Driveline Parts

By Larry Carley c2004

Suspension and driveline parts do not need to be replaced as often as some other auto product lines because of their relatively long service life. Most of these parts are engineered to go well beyond 150,000 miles, and many do. But some do not, and eventually most ball joints, wheel bearings, hubs, constant velocity (CV) joints and universal joints (U-joints) wear out. The lifespan of these parts is mostly a function of mileage. But environmental factors such as rain, road salt, dirt, extreme heat or cold and driving conditions also have an impact.

Most original equipment ball joints on late-model vehicles are sealed for life and have no grease fittings. None are needed because the polished steel ball is encased in a low-friction, self-lubricating polymer bushing. Low-friction ball joints are very durable and can withstand years of normal driving. But they may fail prematurely for several reasons.

One is contamination. If the protective rubber boot that seals the joint is torn, cracks or leaks, road splash and dirt can enter the joint and accelerate wear. If the boot has failed, the joint is doomed to a premature death.

Extreme driving conditions can also pound ball joints to death. Ball joints are engineered to handle normal loads and driving conditions. But there are limits, and when these limits are exceeded, the joint suffers accordingly. Driving 40 miles a day on rough washboard gravel or dirt roads is obviously going to wear out the ball joints much faster than driving on smooth pavement.

When ball joints become worn, the joint loosens up and creates slop in the suspension. The driver may hear clunking noises when hitting bumps or driving on rough roads. Play in the joints may also affect wheel alignment causing undesirable changes in caster and camber. If a bad ball joint is ignored long enough, it may fail catastrophically and break or pull apart causing the suspension to collapse.

When the suspension is checked, the amount of play in the ball joints should be measured with a dial indicator. If wear exceeds specifications, the joint needs to be replaced. Different types of joints have different wear tolerances, so always refer to the specifications in a manual and use the recommended procedure to inspect the joints. Jamming a large crowbar between the control arm and knuckle and prying with all your might is not an approved method of checking ball joints. Pry hard enough, and even a new joint may show excessive wear.

Some ball joints have built-in wear indicators. This type of joint must be checked with the joint loaded (the weight of the vehicle on the wheels).

When wear exceeds specifications, the ball joint has reached the end of the road. Most experts recommend replacing ball joints on high-mileage vehicles in pairs. Why? Because if one joint is worn out, chances are its companion on the opposite side is also nearing the end of its service life. Better to replace both at once than to wait and have to replace the other joint in a few thousand miles.

On vehicles that have short-long arm (SLA) suspensions, there are four ball joints: two upper joints and two lower joints (one of each on both sides). The joints are located at the top and bottom of the steering knuckle and connect the knuckle to the control arms.

If the spring sits on the lower control arm, the lower ball joint is the loaded joint that carries the weight of the vehicle. The upper joint is a follower joint that holds the suspension together but carries little load. Consequently, the loaded joint is usually the one that wears out first.

In SLA suspensions where the spring sits atop the upper control arm, the upper ball joint is the loaded joint. On MacPherson strut suspensions, there are no upper ball joints (the strut and spring support the weight) and the lower joints carry no weight.

The ball joints on some vehicles are press-fit or riveted to the control arms, making replacement difficult. Separating the joint from the knuckle also requires a puller or fork, so if you don not have one of these tools, you should buy or rent one.

CV JOINTS
CV joints on front-wheel-drive (FWD) halfshafts and all-wheel-drive (AWD) halfshafts are surrounded by a protective rubber or hard plastic boot. If the boot cracks or splits from exposure to excessive heat or cold, from old age, or from accidental damage, two things can happen. The joint can lose its vital supply of special grease, and/or dirt and road splash can contaminate the grease inside the joint. Either way, it leads to premature failure of the CV joint.

A classic symptom of a bad outer CV joint is a clicking or popping sound that is only heard when turning. A bad inner CV joint may make a clunk when the transmission is put into gear, or produce a growl or vibration at speed.

Few technicians replace CV joints individually anymore. It is much easier and faster to simply replace the entire halfshaft assembly with one that has new or reman joints already installed on it. Some outboard CV joints can be difficult to remove from a shaft, and the new joint must be locked in place and carefully repacked with grease before the new boot is positioned and clamped in place. It is a messy, time-consuming job, and if it isn't done right, the boot may leak and cause the new joint to fail. That is why replacement shafts have become so popular.

There is a lot of variety in CV joints and shafts, so when looking up a replacement joint or shaft you need to correctly identify the application. This is especially important on older Honda and Chrysler applications that used shafts from a variety of OEM suppliers. With individual joints, the spline count, diameter and length of the joint must be the same as the original. With shafts, the overall length must also be identical. If the vehicle has antilock brakes and the wheel speed sensor ring is on the outer CV joint, make sure the replacement joint or shaft has the same ring and that the number of teeth match.

If you need a boot for a CV joint, buy a premium boot that will provide added durability.

Other items that should be checked when servicing a CV joint or shaft include the oil seals in the transaxle (replace if leaking) and motor mounts. The outer hub nut should be replaced with a new one and tightened to specifications with a torque wrench, never an impact wrench.

U-JOINTS
U-joints are still used in the driveshafts of most rear-wheel-drive vehicles. Unlike CV joints, U-joints are not protected by a rubber boot. They do have grease seals inside the caps that keep grease in and contaminants out. Most original equipment U-joints are sealed for life and do not have grease fittings so no maintenance is required.

As the miles add up, wear in the U-joints may cause a cyclic vibration or noise when accelerating or driving. Play in the joints will often cause a clunk noise when putting the transmission into gear. Any visible play in a U-joint means the joint needs to be replaced. Changing a U-joint is not as easy as it looks because the two ends of the joint are press-fit into the yoke on the driveshaft. A hydraulic press must be used to remove and install the U-joints.

WHEEL BEARINGS & HUBS
In the good old days, all vehicles had wheel bearings that needed to be cleaned, inspected, repacked with grease and adjusted every 30,000 or 50,000 miles. The required maintenance generated a lot of grease, seal and wheel bearing sales. Nowadays, most vehicles have sealed wheel bearing assemblies that require no maintenance. They typically go 130,000 miles or more without a hitch in normal driving conditions. But like any other high-friction part, they eventually wear out. Premature failure can be brought on by water contamination (driving through hub deep water, for example), abusive driving and severe overloading.

The first symptom of wheel bearing trouble is usually noise. A rumbling, growling, chirping or cyclic noise of any kind from the vicinity of the wheels is a good indication that the bearings need to be inspected without delay.

Wheel bearing noise is usually proportional to vehicle speed, and does not change when accelerating, coasting or decelerating (which distinguishes it from differential, transmission or U-joint noise). The noise may change when turning, or become louder or even disappear at certain speeds. If a sealed bearing assembly is noisy or feels rough when the wheel is spun by hand, the bearing and hub assembly needs to be replaced.

If a wheel bearing is making noise, the bearing should be replaced as soon as possible. A catastrophic wheel bearing failure may cause the wheel to fall off.

On some vehicles (many GM models, for example) the sealed wheel bearing and hub assembly also contains a built-in wheel speed sensor for the antilock brake system. If this sensor fails, it will turn on the ABS warning light and disable the ABS system until the sensor is replaced. But the sensor cannot be replaced separately on these applications. The entire hub assembly must be changed. It is an expensive repair, but there is no other option for these kind of applications.

On newer vehicles with sealed bearing cartridges or hubs, the bearing cartridges or hubs are replaced as a unit. No grease or adjustment is required. But on older vehicles with serviceable wheel bearings, the bearings can be taken apart, cleaned and inspected. With serviceable bearings, the bearings are usually mounted in the hub of the brake rotor or drum. On 4x4 trucks, the bearings are in the hub. There is an inner bearing and an outer bearing. Each bearing also has three parts: an outer race in the hub, an inner race that rides on the spindle and the bearing assembly itself (a cage with tapered roller bearings inside). If any of the rollers or races are worn, pitted, cracked or show any damage, the entire bearing must be replaced.

Heat discoloration of the bearings would indicate loss of lubrication or overtightening. If the bore in the hub is damaged or does not hold the outer bearing race snugly, a new rotor or drum will also be needed.

When serviceable wheel bearings are repacked or replaced, new grease seals must also be installed. Reusing old grease seals is risky because they are easily deformed during removal. Grease leaking past an old seal can contaminate the brake linings and increase the risk of bearing failure from the loss of lubrication.

Wheel bearings require special high-temperature grease such as #2 NLGI lithium-based grease or a synthetic wheel bearing grease. Ordinary chassis grease should never be used to lubricate wheel bearings. Always use the correct type of grease. Also needed will be new cotter pins to lock the spindle nut in place, and possibly new grease caps for the hub if the old ones do not fit properly.

In a typical 3,400 lb. sedan, each pair of front wheel bearings as well as the rear wheel or axle bearings support 850 pounds, depending on the front-to-rear weight distribution of the car.

That's a lot of weight to carry for tens of thousands of miles, especially if you're also towing a boat or trailer. The constant load eventually takes a toll on the bearings, even with the proper lubrication and adjustment.

Tapered roller bearings are used in various automotive applications including inner and outer wheel bearings. What distinguishes these bearings from other type of bearings is that like a ball bearing which uses small steel balls between the inner and outer races, to reduce friction, a tapered roll bearing uses rollers for the same purpose. The wider footprint provided by the rollers allows the bearing to support a much greater load.

Also, the rollers are angled so that they rotate in a cone-shaped path. In a straight roller bearing, the rollers are parallel to both races and all the rollers are perfectly cylindrical. But this design cannot handle side forces so a tapered design is needed for applications like wheel bearings, axle and differential bearings that must cope with horizontal thrust as well as vertical loading. Quality bearings are made of high-grade steel, and the inner and outer races (called the cone and cup) as well as the rollers are case hardened (carburized and heat treated) to harden the surface of the metal. This improves wear resistance and the ability to withstand loads.

Tapered roll bearings are precision fit assemblies. So if the rollers, cup or cone are worn or damaged, the entire bearing must be replaced as a unit.

With that in mind, when should the wheel bearings be checked? When the brakes are serviced, when a front or rear axle shaft is replaced or when a steering or ride problem occurs that might be bearing related.

If the vehicle is making cyclic or speed-related noises such as squeaks, chirps, growls or buzzing while driving or steering looseness or wander, those are sure signs of possible bearing trouble.

WHEEL BEARING REPLACEMENT
A major automotive aftermarket manufacturer's study revealed that of the millions of brake jobs performed each year, 55 percent also needed bearing and seal replacements. So why isn't this automatically included in a brake job? Cost is the main reason. Motorists don't want to pay for bearings unless they are absolutely necessary, and many times they are not.

In the trucking industry, the law requires that wheel seals be inspected whenever a brake job is done. Worn or leaking grease seals can allow grease to leak out of wheel bearings, and dirt and water to enter the bearing cavity. Without a proper seal, the wheel end will fall off.

Noisy or rough bearings need to be removed and inspected. If the bearing rollers, balls or races are worn, pitted, cracked or feel rough when rotated as an assembly, replacement is required. Heat discoloration indicates the loss of lubrication or overtightening.

Bearing hub bores should be checked for damage and proper bearing fit. If the bore is damaged or does not hold the race snugly, a new hub, rotor or drum is needed.

When wheel bearings are installed, they should always have new grease seals. Prying out the old seals usually bends and distorts them, even if they are brand new. Do NOT reuse old seals because they can leak grease onto the brake, contaminating the linings causing uneven braking and may cause a brake pull to develop.

Unfortunately, there are some people who pound these parts in like hubcaps instead of using the proper seal tools to assure a precise fit. Consequently, the sealing element won't spin correctly causing the wheel to wobble because it is not making contact with the shaft. On some applications, the shaft has been damaged. Some manufacturers offer shaft repair sleeves that go over the shaft, giving a perfectly smooth sealing surface to seal.

The right fit is so important to the life of a bearing.

Over-tightening adjustable tapered roller bearings is a common error that can lead to an untimely failure. Tapered roller bearings on the front of RWD vehicles are never preloaded. In fact, they are snugged up with no more than 15 to 20 ft. lbs. of torque while rotating the wheel to make sure the bearings are seated. Then the adjustment nut is loosened 1/6 to 1/4 turn, and locked in place with a cotter pin. As a rule, end play should be about 0.001 to 0.005 inches.

Bearing cone and seal installation requires special drivers. Use the proper tools when servicing bearings.

The rear wheel bearings on rear-wheel-drive cars and trucks are usually pressed on and require a hydraulic press for replacement. The bearing must be properly supported during installation to prevent damage. The rear seals or O-rings must also be replaced to prevent possible oil leakage and contamination from the rear brake shoes.

WHEEL BEARINGS FOR BOAT TRAILERS
Boaters need to be reminded of the importance of periodic maintenance and service on their bearings. With trailer wheel bearings, even more frequent maintenance is required if the bearings have been in water. With a boat trailer, annual cleaning, inspection and regreasing is highly recommended (usually at the end of the season).

WHEEL BEARING SERVICE
When wheel bearings are serviced, the old grease need to be removed first and the bearings cleaned and inspected before being repacked with fresh grease.

Bearings must be dry before they are repacked with grease. Also, they should not be spun dry with an air gun because doing so may damage them. A lint-free paper towel should be used to dry the bearings as cotton rags can leave behind fibers that may cause trouble later on. Use a quality high temperature wheel bearing grease (a #2 NLGI lithium-based grease, for example) or a synthetic wheel bearing grease. When the grease is added, about three heaping teaspoonfuls is usually enough for most hubs.

The hub should not be packed solid with grease to allow room for expansion.

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