After reading many posts on mounts I decided to replace the motor & trans mounts on my 1984 300cdt.
While there is noticably less vibration at idle there is a noticable vibration that starts at 40mph which begins to subside when I get over 60mph. It is also very noticable when the car is slowing down and quits when I get below 40mph.
The vibration is definitely not related to the engine speed, only the speed of the car. If I put the car in neutral while over 40 the vibration stops.
When the mounts were replaced they had pretty much collapsed. Is it possible that the new angle of the engine/trans has affected the drive shaft joints?
The car has relatively low miles 150K. The engine runs well & trans shifts & feels smooth other than vibration noted.

Any help would be apprectaied.

Tom H
1984 300cdt 150,000

Would you reread this part of your post.... it seems to be contradictory...

"The vibration is definitely not related to the engine speed, only the speed of the car. If I put the car in neutral while over 40 the vibration stops. "

I guess I should say that the vibration is more related to car speed than engine speed. The vibration does not occur if sitting still and revving the engine up to 4K. It also does not occur while shifting through the lower gears at different engine speeds. It begins in high gear when I pass the 40 mph mark.
If I shift into N at 60 the vibration goes away. If I go back into D the vibration returns as long as the speed of the car is still over 40mph.

I have have gone over many posts dealing with this subject & wanted to include the following:
Replaced engine shocks when replacing the mounts.
Tires are new & balanced.
Vibration comes from center of car.

You might want to examine the drive shaft. Start with the center bearing, check for wobble.

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Shane83SD

The center bearing looks pretty bad. The rubber part surrounding the bearing has separated from the bearing holder. Not sure how long, but the exposed metal part of the holder has a good deal of rust. The bearing itself seems to roll a bit rough as well. The whole thing appears to spin freely inside the holder.
How much support does the bearing holder give to the drive shaft? The old rubber bearing holder did not seem too thick although 20 years may have gotten the best of it.

You'd best replace that pretty quickly. It's an easy job once you have a proper wrench for the large nut near the spline on the driveshaft. Mark the 2 driveshaft pieces BEFORE you seperate them. They are balanced in one orientation only.

Studied MB & Haynes manuals & previous posts advice on how to remove the driveshaft to replace the center bearing.
I did the following:
Monkey wrench & channel locks to loosen the locking nut.
Disconnected emergency brake mechanism.
Dropped exhaust from rubber mounts on rear of car.
Jacked up transmission & removed support brace/plate.
Removed bolts for front and rear of shaft.
Struggled to free drive shaft from flex disk until I looked at the one in the box.
Tapped flex disk guide washers free from drive shaft & it was free. No pry bar needed!
Removed old center bearing bolts.
Removed shaft from car.
Separated shaft & tapped out old bearing.
Pressed new bearing in to new holder & tapped it onto the shaft.
Put shaft back together and did the above in reverse order.
Mechanic estimated 3 hours to do the repair. I was done in 4.

Now having replaced the engine & transmission mounts & shocks and center bearing, lower ball joints and upper control arms the vibration noted above and alot more of the rough engine feel and old car ride is gone. Smooth over 80. It just keeps getting better.

"Removed old center bearing bolts."

Make sure you soak them good in wd40 or simular.

Mine where rusted and one snapped.

Louis.

A bad center bearing carrier will, as you found out, allow the driveshaft to "orbit" at certain speeds and loads, causing vibration.

The usually croak around 150,000 miles or so, just like flex disks, shocks, and engine mounts.

Not a bad job, all said and done, just dirty.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!