Bearings and Hub Bearing Assemblies
The vehicle’s wheel bearings are responsible for letting the wheel spin, the interesting part is that the bearing is able to do this while supporting the weight of the vehicle. A wheel bearing’s longevity depends on a number of factors. Corrosion will contribute to the failure of a bearing. The corrosion on the metal of a bearing near its seal can start to push that seal out and as soon as any contaminants enter the bearing grease that bearing will become compromised, and this is the very beginning of a bearing failure. A bearing’s seal is what keeps the grease that lubricates the internals of the wheel bearing. When that grease is unable to provide proper lubricating of the moving parts the friction from metal on metal contact is greatly increased and this causes excessive wear on the internals of the bearing. When the wear on the bearing progresses to the point that the original contact point of the bearing to the race has slightly shifted, then things like bearing play become noticeable. This is found when attempting to move the wheel in relation to the wheels hub. There should not be any movement but if there is, it is a sign of a failed bearing. At one end of the spectrum the bearing might make a grinding noise that is most notable when turning, unloaded and at a slow speed; or it might whine at high speeds. At the other end of the spectrum an extremely worn and separated bearing can let the wheel completely fall off. Thankfully, your vehicle will give you many signs before this happens.
Another type of bearing is called a taper bearing and this works a little bit differently than a sealed bearing. A tapered bearing system is usually found on older vehicles and it can actually be serviced because it can be removed, re-greased and reinstalled. A tapered bearing is usually found on the front of a rear wheel drive truck or the rear of a front wheel drive car. One example of this is a Volkswagen older than 1999. The taper bearing includes an inner and outer race that is pressed into the actual drum or rotor, and the tapered bearing rollers that fit into that race. When installed properly, the wheel should have the slightest bit of vertical play.
A typical front wheel drive Japanese car will have a front bearing that gets pushed directly into the knuckle. This differs from the hub bearing assembly that is actually bolted to the knuckle of the vehicle. The hub bearing assembly is somewhat easier to install because the bearing has already been pressed into its housing and the hub has been pressed into the bearing, the only thing left to do is bolt the whole assembly in. The former typically involves replacing the bearing and reusing the hub. This is because the hub has to be pressed into the bearing after the bearing is installed into the hub, there is no access to the outer race if the hub were to be pressed into the bearing first. To install the press-in bearing without removing the entire knuckle requires a hub tamer. Otherwise a shop press can be used to push the bearing into the knuckle, however when the entire knuckle is removed an alignment may be required after reassembly.