The vehicle is a 75 300D. During the first part of acceleration, I can feel the engine vibrate then it smooths out it progresses. Motor mounts look good - no cracks, no oil deterioration, etc.

Is it the mounts, or something else?

Any thougts appreciated - Ron

Considering it's a 75', yes I would replace the motor mounts at least. On my 86' the mounts were bad even thought they looked fine. I had the same vibration during acceleration as you and replaced the motor mounts and transmission mount and it went completely away. I am going to replace my engine shocks soon also.

Tank - thanks. Was afraid it was the mounts. I have replaced them, but that was about 10 years ago. Never thought of the transmission mount.

Ron

I just found the source of a similar sounding vibration - it was the center support bearing on the driveshaft. That feels mostly like its in the transmission hump. And in my case you could feel it from a startup through about 45-50 mph. At 45 it tended to drone in and out about once a second.

I had previously given the bearing and rubber support visual check and a shake, but decided to take it completely out for my search on the vibration. It was so loose and dry I could make the bearing oscillate just spinning it by hand. And the rubber mount was significantly torn on the upper side where I couldn't see it until removed from the car.

Probably the original bearing at 325,000 miles.

These bearings are sealed, so it does no good to spray it with something like WD40 as a test.

Ken300D

Ken 300 D - thanks for your input. I guess it is another item to check out.

Ron

Ron:

Deep thumping vibration only on acceleration is diagnostic for a bad tranny mount. Very easy to replace, two screws and a nut, I thnk on your car all you have to do is lift the tranny a bit to get it out -- if that won't work, just drop the crossmember (four bolts) while holding the tranny up with floor jack.

Check to make sure it goes in the right way, there is usually a front and back! Two little bumps on the rear side fit up against the tranny bracket (at least on the 280 SE).

The rubber seat for the center carrier bearing going bad causes vibration at all speeds and loadings, worse under accelation, but always there.

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!

Ron, any luck in correcting the problem yet?

I had this replaced on my car to but for me it had no effect upon acceleration. It would vibrate only when i "reached" certain speeds.

My engine mounts were a different story- when they were bad, I would floor the accelerator and the car would shimmy and shake like an old truck, then shift and -same pattern through the rpms all over again in the next gear. It seemed like the harder I hit the pedal, the more it would shake.

When I first got the 300TD a few weeks ago I could feel a vibration from about 40-50 mph. I changed out both half shafts and the rear flex disc and the vibration is no longer there. Not sure which of the two resolved it though.

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Jim