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Wheel Bearing Lessons

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Wheel bearings are either of the ball or tapered roller variety. Front-wheel bearing applications are an angular-type ball bearing, which will accept greater thrust loads than a Conrad-type bearing, and will accept a 100% load in the radial or thrust position and any combination of a 100% load. A tapered roller bearing will accept both a radial and a thrust load.

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All wheel bearings come in sets that consist of an inner and outer bearing. As is the case of a rear axle that uses a “C” clip to retain the axle to the ring gear carrier, the ring gear carrier bearings handle the thrust load and the straight roller at the flange end carries the radial load.

Some rear axles will have a cartridge-type wheel bearing set containing either ball or tapered rollers.

Seals

Basic wheel bearing seal construction remains the same, consisting of a metal retainer and seal. The primary sealing materials have changed from felt to rubber products, ranging from Buna-N to Fluoroelastomers, yet felt is still used as a dust shield for the primary seal.

A seal is only as good as the surface it rides on, and that surface needs to be lubricated. If the seal lip runs on a dry surface, it will overheat and become brittle. A scratch or gouge can damage the sealing lip and cause the seal to fail. The seal must be lubricated before it is installed to prevent it from running dry. A small amount of grease on the back of the seal and a film on the spindle is recommended.wheelbearingrunout

Don’t force the issue by getting a bigger hammer – instead, it is highly recommended that you use a seal installer. The installer will prevent the seal from being cocked when it’s installed. A shaft protector should be used when installing a seal over a splined shaft. The dust cap is also a vital part of the sealing system. A little extra care and a brass drift can make the job a lot easier.

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Vehicle makers are setting new specifications for sealing and drag on some new vehicles because a tight seal and fuel efficiency do not go hand in hand. To meet these OEM goals, some seal and bearing manufacturers are changing designs and materials in an effort to improve the overall performance of a bearing.

Wheel Bearing Adjustment

A wheel bearing that’s out of adjustment can reduce bearing life and can affect more than just the bearing. An out-of-adjustment bearing affects the operation and service life of the spindle, wheel seal and brake components. It’s important to adjust the wheel bearing end play to the proper specifications. If the bearing set is adjusted too loose or too tight, it can cause the bearing to fail prematurely. In fact, a recent survey showed that more than half of the bearings on the road today are adjusted incorrectly.

Bearing adjustment wasn’t critical to braking performance until the introduction of disc brakes. The caliper is mounted directly to the steering knuckle. If there was too much end play, the piston would knock back in the caliper, resulting in excessive pedal travel. The use of direct mount calipers is returning in high-performance vehicles.

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The following procedure is one method for adjusting the end play in a wheel bearing set.

Tighten the adjusting nut while turning the rotor or drum. When the effort to turn the rotor or drum increases, a preload is placed on bearing assembly and all raceway surfaces are in contact, providing no end play. Back off the nut one flat to allow insertion of the cotter key. The end play can be checked with a dial indicator. Mount the indicator with a magnetic or mechanical base as close to the center of the hub as possible. The indicator tip is set on a smooth surface at the end of the spindle. Push the rotor back and set the indicator to zero. Then pull the rotor or drum out and read the dial indicator.

Allow 0.004-inch (0.100 mm)  ± 0.003-inch (0.076 mm) of end play, then lock the nut with a new cotter pin. Whether you are checking a conventional wheel bearing or hub bearing, the best tool for checking adjustment is a dial indicator. Many four-wheel-drive vehicles and most trucks with a load rating of one ton and higher use a full floating axle. The axle has a bearing set, spindle and hub. The same adjustment procedure can be used for these applications.

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Over tightening adjustable tapered roller bearings is a common error that can lead to premature failure. Tapered roller bearings on the front of RWD vehicles are never preloaded. They’re 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 a turn and locked in place with a new ­cotter pin.

As a rule, end play should be about 0.001-inch to 0.005-inch. There should be no play on most FWD cars, but up to 0.010-inch of play in the front bearings may be acceptable on RWD vehicles.

Hub Bearings

In the late 1970s, the hub bearing began to appear on FWD vehicles. It was a sealed, lubricated for life, pre-adjusted bearing with a mounting flange attached to the strut knuckle, or rear axle flange and a hub for the rotor, wheel and CV joint. The bearing could be either a ball or roller type. Passenger car and light truck hub bearings are not adjustable.

The hub is directly affected by the condition of the bearing. The driver may first notice a noise coming from the wheel of the vehicle when the steering wheel is turned. There will be noticeable end play when the wheel is unloaded. Checking with a dial indicator will show an end play greater than 0.004-inch (0.100 mm).

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Bearing end play can also affect a wheel speed sensor and cause an intermittent ABS trouble code. If the bearing flange has runout, that runout will be magnified at the rotor friction surface. A runout of 0.0005-inch (0.00254 mm) at the bearing flange could result in 0.001-inch (0.0025 mm) runout at the rotor friction surface.

As electronic stability control (ESC) braking systems become more complex, the wheel bearing will still be the central component in the system’s operation. With the introduction of the electronic wedge brake (EWB) just around the corner, the caliper, wheel speed sensor and chassis controller will become the ABS system. These changes will require greater care in the servicing of the total suspension system.

Tools

To avoid damaging a new bearing, the bearing inner race must be carefully pressed onto a shaft, and the outer race pressed into its bore. Hammering a bearing in place can result in the rollers or balls dimpling the bearing races and causing premature failure.

Most bearings have about 0.001-inch of interference-fit built into an axle shaft or bearing bore, which means that these types of bearings must be pressed or driven into place. Tapered bearing cups or outer races should be driven in place using a special aluminum driver. In an emergency, an old bearing race cut through on one side with an air-powered “whiz wheel” will serve the purpose.

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Special tools are also available for pressing bearings into a steering knuckle. Installation of bearings into an aluminum steering knuckle or housing can be expedited by using an electric hot air gun to gradually expand the housing without melting or distorting the metal. Lastly, always adjust a tapered roller bearing by torqueing it to 15-20 ft.-lbs. and spinning the hub to center the rollers in the races. Back this initial adjustment off 1/8 or 1/4 a turn and retorque the bearing to manufacturers’ specifications. A typical final torque of 20-30 in.-lbs will leave zero end play and a slight amount of preload on the wheel bearing assembly.

Whether you’re installing a ball, roller or sealed bearing assembly, using correct procedures and tools will ensure a comeback-free wheel bearing installation.

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