I replaced the donuts and bushings on the driveshaft hoping it would stop the bucking this car does sometimes, but it didn't. It seems to happen in 2nd through 4th gears when lugging the engine down. It feels like if you stepped on the gas, let off, stepped on, let off, etc. It will get worse with each pulse if I don't either up shift or push in the clutch, to the point of real violence. I've had plenty of different cars and trucks but none that acted like this. Any ideas?

I have no solid ideals on the actual cause. When confronted with a mechanical problem in a car I cannot relate to I always did a standard tune up first.

In many cases the problem was located or some indication of where it was located was found. I would make sure the valves had reasonable clearances and the injection pump was properly timed in this case. Why the symptom increases in violence is especially challenging.

I have to assume you are not taking the engine down near it's stalling point. If the motor mounts are totally shot for example the injection pump linkage may be oscillating with a moving engine. It also almost sounds like you are losing a cylinder at lower loaded rpms. Best of luck and wait awhile. People with more productive opinions should post.

My old 1980 euro 300d w/ 4 speed manual did the same thing, it was unpleasant. I figgered it was the result of the torque of the diesel, the slop in the 200k drivetrain and the flex of the flex discs synergystically combining to produce some unholy oscillation.

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Cheers,
Robert

There you go. Don't lug the engine, its not good for it. Google "lugging engine" to see why.

put it in neutral and coast for awhile ,,,,whats the rush is my moto

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1980 300sd turbo 284k (parts car with bad tranny}
1980 300sd turbo 145k (daughters daily driver)
1985 300td turbo 215k (my daily driver)

This has happened to me a few times, but I assumed it was because I was shifting at the wrong time. When I shift at the right speed/rpm for the gear, it never happens.

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