Hi, my name is Joe and 3 weeks ago I bought a PB 96 SE, with only 70k miles. Everything seems to be working fine, except the ride. Changed tires but same. The car is very unstable specially in the back. Even the smallest imperfection in the road makes the car shake the back. Looks like the shocks are bad, but not. The only thing that I can see is the steering wheel not straight. Any idea? Thanks

Did you just rotate the tires or buy new tires?

What'* the Tire Pressure??

Have you had the alignment checked on this car yet???

This sounds a lot like my problem, my rear springs were basically shot. My alignment was off even after getting the car aligned and the rear would shake horribly. Finally it got to a point where the rear of my car was sagging. I changed the rear coil springs it it fixed all of those problems.

Check your ball joints and rear tie rods

Hi again and thank you all for the replays. I didn't have much time recently to write, but I do have new tires (2k miles old) whick are wearing very fast, specially in the rear. Looks like positive camber cause the outside already show some even wear...
Today I was driving home and for no reason TC and ABS lights came on. I'm starting to think that the car is going to be a headache... :(

Get the car aligned, that'* your problem. Tires wearing fast and unstable ride especially over bumps is indicative of incorrect toe. If you bought an older car and anticipate not taking care of the basics, yes, it'* going to be a headache.