What Are Wheel Bearings?

by William Zane

Wheel bearing are one of the most crucial components of a car's suspension. They are usually located in the hub (the part that the brakes and wheels are attached to) or even the brake drum or rotor itself. Wheel bearings allow the wheel to rotate freely as the car travels down the road. Most cars have an inner and an outer bearing on each wheel.


A wheel bearing is a simple device made up of two main components, the bearing itself and the race. The bearing itself consists of a metal housing that is pressed over a row of ball bearings that circle the metal housing. These ball bearings in turn ride on the race, which is a very smooth metal surface. When a wheel is rolling, the action of the ball bearings rolling against the surface of the hub that allows the wheel to spin smoothly.

Wheel Bearing Problems

Problems with wheel bearings arise from wear, which can be caused by a variety of factors. Bearings are protected from dirt and debris by oil seals. If these seals fail and dirt finds its way into the bearing, damage can occur to the bearing and the race. Another factor can be long-term wear, affecting the bearings' ability to function properly. If a bearing falls apart completely, it can render the car undriveable and dangerous. The brakes will not function correctly and the wheel will not stay in its proper orientation.


Symptoms of a bad bearing are noisy rubbing as the car is driven and that usually gets louder as speeds increase. If the bearings are very worn, another symptom can be vague steering, vibrating suspension and darty behavior from the suspension as the wheel moves unevenly around the bearing.


Bearings can be checked by jacking up the car and pushing on the wheel. If there is excessive movement of the wheel on the spindle, it's probably the bearing. Wheel-bearing maintenance is relatively simple but time-consuming, since the wheel, brakes and hub need to be removed. Once the bearing is visible, check the bearings for wear and the races for any scratches or wear. Clean everything thoroughly and repack the bearings with a generous amount of bearing grease. This should be done every 20,000 to 30,000 miles.


Replacing bearings can be time-consuming, but most accomplished home mechanics can do the job. It involves removing the wheel, brake and hub. Once the hub is off, the bearing races are removed and new ones pressed in. This is usually the most difficult part. Once the bearings are packed and installed, everything is reinstalled in the reverse of removal. Refer to a workshop manual for detailed instructions about your car's model. This should be done every 40,000 to 50,000 miles.


A destroyed wheel bearing can result in a vehicle that is difficult to control. If you suspect that your bearings are bad, do not drive the vehicle until it is fixed or you know it is safe.


About the Author

William Zane has been a freelance writer and photographer for over six years and specializes primarily in automotive-related subject matter among many other topics. He has attended the Academy of Art College in San Francisco, where he studied automotive design, and the University of New Mexico, where he studied journalism.

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