A wheel hub is mounted via an integral mounting flange to the chassis of a vehicle; the wheel of the vehicle is mounted on the other side. To allow the wheel to turn effortlessly the hub contains a bearing assembly. The hub is virtually indestructible as it is machined or cast from heavy metal, when there is a need for a wheel hub assembly replacement it is because the bearing has failed.
How to tell when the hub assembly needs replacing:
The entire hub assembly is a “no maintenance” item even though it takes the weight of the vehicle as well as shock loads while the car is in motion. The bearings are subjected to lateral loads when your turn a corner and radial loads of course, the bearings are designed to last for hundreds of thousands of revolutions and to rotate at thousands of RPMs. The bearings that are used in the engine of your car are kept reasonably cool and well lubricated with engine oil; this is not the case with wheel bearings. Wheel bearings are pre-lubricated and sealed during manufacturer.
In the past, it was possible to lubricate wheel bearings; modern vehicles are almost always manufactured using sealed bearings. Even if the bearings are pre-lubricated and sealed, eventually they will begin to fail and when they do a wheel hub assembly replacement is the easiest, quickest and least expensive solution.
How does a bearing fail?
A wheel bearing will fail when either the rollers or the bearing race begins to pit. Although bearings are manufactured to an extremely high tolerance, sooner or later slight wear will begin to take place, when it does traces of metal from the race and rollers gets into the lubricant, this only accelerates the wear and the eventual destruction of the bearing. As the bearing has to carry the weight of the car, once bearing failure is imminent you will know because of odd noises.