Drivetrain vibrations - 323i Manual Trans. MY2000

[cgdR]

After changing transmission (used), clutch, flywheel, flex disk, center support bearing, and rear differential bushing (Heavy Duty), I have 2 probably related vibration problems:
1) full throttle in 2nd and 3rd produces pounding, presumably at the CSB.
2) low-medium throttle in 3rd, 4th, 5th produces a loud rumbling sound throughout the cabin. Coasting is fine, and at full-throttle the noise is less perceptible.

Given the inability of the first shop to resolve the issues, I took it to a shop that specializes in drive shafts. They changed the CSB again, the U-joint, and rebalanced the shaft. That pushed the RPM for the pounding/slapping from about 3000 to 5000, but the problem remains the same.

Any ideas? Could any of the "new" parts be the culprit? Engine mounts failing? Drivetrain alignment problem?

PS. The box was changed at 135,000 mi because the 3rd gear did not engage after my daughter learned to drive in the car. However, the car's transmission has had issues for a very long time: the clutch would often shudder since new, and the 5th gear detent had been stuck for several years. Otherwise, the car was very smooth.

[HBWT]

good insight.

[skiwi]

Did you have any luck with a response to your question? I have developed a very similar drive train vibration after changing my auto trans...

[cgdR]

The car is back at the shop that had assured me that replacing the U-joint, rebalancing the shaft, and correctly indexing the splines would fix the problem. Since that job didn't do it, they're on the spot to find the issue. They're going to start by checking all engine/trans/diff mounts, but I am concerned that after that they may be soon running out of ideas.

[skiwi]

Interesting....hope they sort it out.

I know the diff mounting on my car is definitely shagged and the trans and engine mounts are probably well past their prime...

I will need to look into the other areas you mentioned.

Thanks for the info and please keep us posted!

[cgdR]

It took months of perseverance, but my vibrations are gone. It looks like a left engine mount finally did it. The mound had not been changed before because it did not look bad. The tech also replaced again the CSB and the flex disk which had been damaged in a few thousand miles by either the vibration or an improper installation. Seems simple, but it looks like a simple component can become a bit worn and throw the whole drivetrain catastrophically out of tune.

My initial fear was that one of the parts that I had gathered was responsible (used trans and new flywheel and clutch from eBay, other parts from lots of different vendors.)

[skiwi]

A fairly easy fix, and not too expensive! Thanks for the feedback, I'll definitely look at replacing mine now.