Brakes: Part 6 (Bearings and seals)

Another set of components that are related to brakes but rarely talked about are bearings, hubs, and seals. If any of these parts needs to be replaced when doing your brakes it will add a considerable cost, so let’s discuss each of these.

A hub is the assembly that houses the wheel studs, so the rotor sits flush against it. Hubs really only need to be replaced for a couple of reasons. In the same way that a rotor can warp, a hub can as well, especially if the vehicle has been involved in an accident like hitting a curb. But, because warpage is possible, many manufacturers these days are recommending, if not requiring, that rotors be resurfaced on the vehicle with an “on-car lathe.” Instead of removing the rotor to resurface on a bench lathe, it is done on the vehicle with a different machine. If the hub is warped, the machine will automatically compensate for that when cutting the rotor to minimize or eliminate runout (remember that word?). Otherwise, a rotor cut on a bench lathe on which the warp has been cut out will be placed back on a warped hub, thus not solving the problem. Another reason a hub may need to be replaced is if a wheel stud is spinning in its hole. Since the hub is threaded to hold the stud in place, it will need to be replaced. The last reason to replace the hub is if the bearing is bad and it only comes as a hub/bearing assembly. These are expensive, and found on many cars.

A bearing is a ring of ball, or cylindrical, bearings. It is pressed into the back of the hub. When bearings start to go bad you may hear a grinding sound if the bearing is dry. Most of the time, bearing noise sounds like a low hum while driving, and may actually go away when turning left or right when force and pressure is relieved on that particular wheel. Many times, it is difficult to differentiate bearing noise from a bad tire. Therefore, there are two more ways to pinpoint this problem. In our shop we will elevate the suspicious wheel, put the engine in drive, and slowly press on the gas. If the sound is not there, then it must be a tire problem since the tire is no longer making contact with the ground. The third method involves raising the wheel, grabbing the top and bottom of the wheel, and trying to tip it in and out. If it moves at all, even a miniscule amount, the bearing has play and is causing the noise. If the grease in the bearing looks contaminated and the bearing is in good condition, expect to at least pay for a ‘clean and repack’ on the bearings to lengthen their lifespan. Be aware that some vehicles have inner and outer bearings (both should be inspected thoroughly), and some are pressed into a hub as described above. Trying to remove bearings from a hub assembly is possible, but will almost always damage the bearing.

People don’t normally associate these parts when they think of brakes, but they are important components to the proper operation of them as a whole. I just don’t want you to be surprised when this stuff comes up.

Lastly, we have seals. Almost always seals are associated with rear drum brakes. Some rear brakes (especially on duallys and Heavy Duty trucks) can only be worked on by completely removing the rear axle. The backing plate on the brakes normally has a small slit to look inside and check the thickness of the brake shoes. Most shops will not disassemble these rear brakes unless you are ready to pay. This brake job is expensive because there is a lot more labor involved, and since you will also need to replace the axle seals and the differential fluid that will be lost when the axle is pulled. This would be a great time to perform a differential service, which is on the factory scheduled maintenance list. The shop should remove the differential cover to completely drain the fluid and then reinstall it with a new gasket.