Bearings Keep On Rolling

Wheel Bearing Cros Section
Wheel bearings keep the world rolling. The bearings allow wheels to rotate with minimal friction while keeping them centered and aligned on their respective axle shafts or spindles. Wheel bearings are designed to last the life of the vehicle, but they can fail at any point after 100,000 miles. Hard driving, aggressive cornering, and driving on rough roads accelerates wear. Water (especially salt water) can also ruin a set of wheel bearings if the water gets inside the hub when a vehicle is driven through hub-deep flood waters. Water inside the hub will degrade the grease and precipitate the formation of rust that corrodes the bearing surfaces. A bad bearing will make a chirp, growl, hum or squeal that increases in frequency with vehicle speed. The sound may come and go, or only be noticed when driving at a certain speed, but should be investigated to find out what’s causing it.

The wheel bearings on most late-model front-wheel drive (FWD) and rear-wheel drive (RWD) cars and trucks are part of a sealed hub assembly or are inside a sealed cartridge mounted in the steering knuckle. Since this piece is sealed, it is difficult to inspect directly. The best way to check a wheel bearing is to rotate the wheel by hand while feeling for looseness or roughness, and to rock the tire to check for play. Most sealed wheel bearings should have almost no play (less than .004 inches at most), and should be replaced if found otherwise. If one bearing fails, the others will soon follow, so it is recommended that all are replaced at the same time.

The wheel speed sensors in some hub assemblies can be replaced separately if there is a problem with the sensor, but on others the entire hub assembly has to be replaced if the sensor calls it quits. Its an expensive fix, but without it, the ABS will not work. Replacing a bad wheel bearing often requires special tools such as a hub puller or a hydraulic press. It takes a certain amount of skill to do this job correctly, and if done wrong the new bearings may be damaged or fail prematurely. A new hub or axle nut (and cotter pins) should always be recommended to customers who are replacing wheel bearings. New grease seals are a must when replacing a serviceable wheel bearing on an older vehicle. Always use a high-temperature wheel bearing grease that meets or exceeds the requirements for a moly-fortified NLGI No. 2 Grade LB Lithium 12-Hydroxysterate extreme pressure grease, or NLGI No. 2 Grade GC-LB Lithium Complex extreme pressure grease. Conventional greases and synthetic greases are NOT compatible and should NOT be intermixed. If non-compatible greases are intermixed, the combination may break down and separate at high temperatures leaving wheel bearings high and dry without adequate lubrication. On older vehicles without sealed wheel bearings, cleaning, inspecting and repacking the wheel bearings every 30,000 miles is usually recommended.

On boat trailers, the wheel bearings should be repacked every season due to the fact that the wheels are often submerged in water. Your customer may need a seal driver to install new grease seals on an older vehicle. Using a driver is important to make sure the seal is driven in straight, and is not bent or damaged during installation (which could cause it to leak). When replacing wheel bearings on older vehicles that do not have sealed bearings or hubs, the bearings must be adjusted to allow the amount of play specified by the vehicle manufacturer. In most cases, tapered wheel bearings should NOT be preloaded.