Originally Posted by yogarda

Hi All,

This is regarding my 1983 300D. Sorry for the long explanation below but this problem is detailed and has some subtle distinctions. I've read many posts about this and none has yet solved my problem.

Early last July my car suddenly developed a vibration in the driveshaft that is related to engine torque and specific speeds. Everything about the car had driven smooth and fine until I turned up an unusual road where there was both a sharp right turn and a steep incline at the same time. While climbing the (rather long) hill I reached 30mph and suddenly there was a violent shaking that eventually ripped the rubber mount that holds the propeller shaft bearing.

The character of this vibration is that it occurs only between 25-30mph, only under heavier torque or climbing any incline. I can let up on the pedal and accelerate slowly and prevent the vibration. I can accelerate moderately downhill and there is no vibration. It is definitely torque-related, and related to the angle of the car.
If I turn hard left, the vibration may not happen at all through 25-30 and beyond. If I turn hard right, it will be worse. This is reminiscent of the day this first occurred.

Over the past year I have ripped through TWO center bearing mounts. I have read many posts regarding similar vibrations and changed nearly everything that wears in my driveline. I'll start from the front of the car and note whether each part replaced seemed to be needed or not:

Engine mounts - needed
Transmission mount - maybe needed
Front flex disc - needed
Front propeller shaft centering bushing - not needed
Propeller shaft bearing - not needed
Propeller shaft bearing mount - ripped twice, I'm on my third
Rear flex disc - not needed
Rear propeller shaft centering bushing - needed
Differential mount - not needed
Both rear axles - 1 had a torn outer boot
Rear tires - eventually needed but not when the problem developed
Rear alloy wheels - I have a spare set for snow tires and the problem did not change with either set of wheels

The propeller shaft U-joint feels a little less smooth when bent to extreme angles but seems smooth at the minor angles needed when driving. I believe I've replaced every other relevant part. And yes, when the propeller shaft has been separated it was marked and reassembled in the correct alignment.

The problem developed so suddenly and has stayed so consistent that it isn't like a rubber part started to wear and is slowly deteriorating. Also I'd think if the shaft itself was out of balance it would shake regardless of the amount of torque being applied. The fact that shifting the car's position (via hard left or right turns) changes how it drives when straight... it's just plain confusing.

Does anyone have any other ideas for me? My plan of last resort is to put it in the dealer and ask them to run it on the lift to see if they can see anything.

Thanks as always for your time and your Borg collective brain!

Garrison