A hub bearing assembly in a rear- or four-wheel drive vehicle connects the axle shaft, wheel and brake rotors to the chassis of the vehicle. Typically, the axle shaft runs through the center of the assembly, which consists of an axle bearing, axle seal and outer support piece.
A damaged rear hub bearing assembly can cause uneven tire wear, instability while driving and, in the extreme case of the assembly failing completely, catastrophic failure of the rear axle. The assembly sits behind the brake rotors and is typically bolted to the chassis to provide stability. To service or review the rear hub assembly, it is necessary to remove the brake rotors.