I have an '81 300 SD that gives off a rather harsh vibration while accelerating. You really feel it between 15 and 25 mph coming up through the floorboard and gas pedal. I was told by a Mercedes mechanic that it was a bad universal joint. It did remind me a lot of a similar problem in a BMW 325 which was indeed remedied with the installation of a new (rebuilt) driveshaft. I pulled the Mercedes driveshaft out and there seemed to be a notching effect in the universal -- that is, it would pop into a home base position which was straight ahead on both sides. Oh dear, one rebuilt driveshaft later, I still have the problem. I'm hoping it's not the tranny which seems pretty smooth all in all. Could it possibly be a bad torque converter? I have so little experience with automatics that I'm just guessing. I throw myself at the mercy of Mercedes master minds.