A wheel bearing consists of a number of high precision steel balls that are held in place by a cage. The ball and cage assembly in turn ride between an inner and outer ball race. The purpose of a bearing is simple, it carries a load and helps the wheels rotate with minimum friction and minimum heat. Although wheel bearings are associated with cars they are used on all types of vehicles from skate boards to bicycles to aircraft.
When used in a car the bearing inner race fits on the axle while the outer race fits in a hub; the hub is that which the car wheel is bolted to.
The sound of a bad bearing:
- It is actually quite difficult to diagnose a bad wheel bearing as the car really needs to be driven to exactly replicate the noise. In the event you believe a rear wheel bearing replacement is required there are a couple of pointers that can help in isolating the source of the problem.
- If the bearing seal has failed the noise is quite faint at first, over time the noise becomes increasingly louder. The noise is similar to that you hear when you drive over a rumble strip on the expressway, although not as loud.
- Accelerate the car up to about 40 MPH, slowly sway back and forth, shifting the weight from the center to one side and then the other. Pay attention to the sound, does it get louder when you sway one way or the other? The damage will be on the side opposite the direction you are turning.
- A rear wheel bearing replacement is not always required, tires that are out of balance and become scalloped on the tread surface will also make a noise at speed; the noise is similar to that of a bad bearing.
Rear Wheel Bearing Replacement
Rarely will a wheel bearing fail immediately; you normally have ample warning before it has to be replaced. There are two schools of thought about replacing both sides at the same time; this is a decision that is best made after discussions with your mechanic.
As replacing a rear wheel bearing can be expensive it only stands to reason that you should insist on replacing the failed unit with an equally high quality, OEM equal, bearing and hub. As the wheel bearing is directly related to the safety of the occupants of the vehicle, never buy and fit an inferior part, it will only end up costing more in the long run.