Is it hard to change rear wheel bearings on a 1981 BMW 320i. I am reading the book and it talks about shims and how to measure the length and so on. The doesn't show a good picture of it.
The measuring of the bearing seat bore depth is only required when replacing a trailing arm assembly (it was done when the car was assembled new, at the factory).
If you are simply replacing bearings, this is not required. It is VERY IMPORTANT to re-install the shims in their original locations. Don't mix them side-to-side.
The shims adjust for manufacturing tolerances for axial bearing preload.