I have 1986 300E manual with 200,000 miles. I have a proble , when I am driving at any speed and I downshift to accelerate The whole car twists the backend jerkes to the left and the front end wants to take off to the right. I assumed this was a suspension problem because everything was original. I replaced the Motor mounts, trans mount, and ,steering dampner. I also put in H&R springs and Bilstien sport springs. I have new differential mounts but I am waiting till I get my rear sway bar before I drop the subframe. Anyway I still have the jerk in the suspension and it is driving me nuts. Please Help!

Try this thread: http://www.peachparts.com/shopforum/showthread.php?threadid=13126

Well, you have replaced most of the flex items in the drivetrain, except the diff mount bushings. Guess what???. Do you still have the OEM bar in the rear. This sounds like torque steering the rear end. Something is loose back there. The W124 can be shifty when applying full power to a less than tight rear drive. Also, they are sensitive to the tire pressure in the rears. Make sure that's on spec.

It's been suggested many times (here and in other threads), but what you've probably got are worn multilinks in the rear suspension. I had this problem, and it took the replacement of all ten links, plus the differential mounts, to fix it.