Rear wheel bearings are not nearly as complicated as front wheel bearings and we tend to not think much about them. But there are a few things worth going over because the rear wheel bearings do more than just allow the tire and wheel to go around and around. They also keep the rear tires and wheels on the car!
This is not true. The axle housing has a grease seal in each axle tube. The axle itself has a machined journal for this seal to ride on. The purpose of this seal is to keep the gear oil from getting into the area where the rear wheel bearing rides. But many people are confused because Ford uses rear axle flange gaskets for the axle retainers.
The axle retainers are the flat plates with the four holes in them that bolt to the axle housing and hold the rear wheel bearings in place. In fact, Ford has two of these gaskets per side. One for the rear brake backing plate and another for the axle retainer. The backing plate is sandwiched between the rear axle housing and the axle retainer and has these gaskets on both sides. These gaskets are designed to keep the brake dust out of the bearing, not to keep gear oil in. But I've seen people change them, even use silicone on them, to stop gear oil from leaking onto their rear brakes. Of course what they actually need to change is the axle seal.
I purchased a new rear wheel bearing kit which also included the axle bolt. For the B5 S4 ('00-'02), there are two different sets of possible front uprights. The early '00s had aluminum and after that they were changed to cast iron. The cast iron ones have press in bearings as seen below, while the aluminum ones come in a housing which bolts to the upright. I don't know if the rear uprights also differ like the front ones.
New rear wheel bearings with their respective retainers. Our Classic Mustangs all came from the factory with the smaller diameter rear wheel bearings as shown on the left. However, due to rear end swaps, it's possible to find them now equipped with the larger style as shown on the right