My '91 300E has developed an unusual (to me, anyway) vibration. It's nice and smooth all the time except: when traveling at 45+ MPH and the engine is pulling pretty hard. IOW, you're driving on the highway. All is fine. You start up a hill. The vibration starts. Take your foot off the gas and it stops.
It's not dependent on engine speed. When the vibration starts, if you pull the shifter back to 3, the vibration stays the same.
It's not really like out-of-balance wheels. It's more like a rumble throughout the car.
The motor mounts were just replaced and the transmission serviced. I noticed the vibration the first time on the highway after that. A coincidence, perhaps.

Ideas and opinions?

Thanks for your help.

You may want to take a look at the tranny mount.
Changing the motor mounts raises the engine back to specs and will put a strain on a weak trans mount. [ which is really the rear motor mount]

Hi,
I believe it is the U-Joints on your drive shaft that is causing it. I had a similar problem where it would vibrate between 35-45 mph acceleration and would go away after that. I replaced the all the U-joints (rt, center & left) even though only the left one was bad. Cost me around $100 for parts and $120 for labor. Hope this helps.
smk_texas
92 190e 92K