Wheel bearings are an important part of an automobile, as they support the weight of the car while allowing the wheel to spin with little friction. Wheel bearings are subjected to a lot of stress and will eventually wear out and need to be replaced.
The physical stresses placed upon the wheel bearing causes rapid temperature changes inside the bearing. This results in changes to the pressure inside the bearing that may cause the seal to fail. If the grease inside the bearing escapes, the bearings will not properly operate and will begin to wear out.
Water and salt from the road surface are constantly coming into contact with the wheel bearings. These materials can cause the wheel bearing housing to physically corrode, but more likely will simply work their way into the seal and cause the bearings to wear and fail to work properly.
Wheel bearings are subjected to high levels of heat created by the rolling friction of the vehicle. This cycle of heating and cooling causes the metal in the wheel bearings to expand and contract frequently. While the hardened steel is designed to withstand this, as time passes, the metal will weaken and eventually fail.
