In Reply to: Suspension bottoms posted by ken on March 28, 1999 at 00:38:55:
If you're sure the car is bottoming and that the thump is not coming from a loose suspension component, and if you've replaced the shock correctly, then it sounds like your spring has collapsed. Check the ride height (distance from the lowest edge of the wheel to the top of the wheel arch on the body) on both sides. It should be the same +/- 1/8 inch.
Also, shocks should normally be replaced in pairs. So should springs, if that's the problem.
If you're not sure it's bottoming, it could be any of the suspension components that might have a worn bushing or a loose bolt, and check that the shock mounting bolts, top and bottom, are tight. It's possible that the upper shock mount (a metal cup with hard rubber center that accepts the rod of the shock) could be torn, but that's pretty unusual in the rear.
"Thumps can be hard to find without expert help. I chased one in the front when I bought the car last year; went through control arm ball joint, then thrust link ball joint and bushing. That helped but didn't eliminate. Finally replaced right (swore the noise was on the left) sway bar link and that finished it. My belief is that all three were worn out.
'90 535i 5-spd, sharked, stage 1