Ok, so I've had a vibration that varies by speed for a while now with my '90 245 and it really chaps my rear because I have not been able to track it down and cure it yet.

The problem:

I get a short wave vibe at 25mph that seems like the rear u-joint (similar to when the rear UJ seized on my original DS), but it goes a way really quickly. Only seems to occur right at 25mph.

Things are relatively smooth until about 45mph where a medium to long wave vibration is felt through the steering while and remains until about 55-60mph where it becomes a long wave vibration felt more so through the body of the car than the steering wheel. Vibration is long but more apparent 60-80mph.

The steering wheel vibrates but it does not wobble back and forth as if the car is out of alignment. ALL wheels have VERY even wear since new and have been rotated. Because of this, I don't feel as though the tires are effected by the vibration. Vibration is not effected by braking, brakes are about two years old and stop strong and smooth.

Components:

The rear has adjustable torque rods and panhard bar from IPD; Driveshaft operating angle is proper. Trailing arms have been replaced, along with bushings; I thought my right TAB might be bad (changed the right over a year ago, but didn't do the right)when I stab the gas at any speed, 8/10 times it will result in a thud somewhere in the drive line. The bushing looked decent, but I installed one of my Kaplhenke TAB's anyway (I'll do the other soon enough); alas, the thud and vibes remained.

Center support bearing was changed less than a year ago.

Motor mounts are about a year old, but a bit gummy; Trans mount is about 6 months.

Front Suspension:
Everything as been changed, a few times in fact. New control arms and bushings, new ball joints, inner tie-rods and ends, 25mm sway (rear is 25mm too)with Kaplhenke endlinks. I've had issues with struts and gland nuts coming out killing struts and clunking like hell, both struts are good now and tight. I used to have a knocking when turning and going over bumps at slow speed, but that was solved with the Kaplhenke endlinks as they cleaned up the slop at the bottom of the endlink. I hear a binding noise when I make sharp left turns, my guess is a ball joint issue; perhaps slop in the ball joint stud because the nut is loose?

I'm going to give the front suspension a thorough inspection this weekend to see if anything is amiss. If it remains I'm going to start poking around my driveline more; maybe rebuild my old driveshaft and have it balanced. What about the output shaft bushing? Would this cause this? It doesn't seem loose when I grab the driveshaft and check for play.

I need help you guys, its so frustrating to put so much time, effort and money into something only to still have issues.