Vibrations, CSB/driveshaft issue

[evilnickwong]

Recently I had a clunking noise from a torn CSB, so I had that along with the guibo changed on my M40 '91 318i.

When my mech took the old CSB out, it was a slim bracket version, I found a similar pic on realoem from a '84 M10 318i, like this:

http://www.realoem.com/bmw/showparts.do?model=1372&mospid=47271&btnr=26_0123&hg=26&fg=10

The new one from the dealer is a bigger version and looks more like the kind I see nowadays for E30s, this one:

http://www.realoem.com/bmw/showparts.do?model=AJ52&mospid=47273&btnr=26_0012&hg=26&fg=10

Before installation:
1) Noticed that the CSB flange was facing the wrong way and the driveshaft was angled a little.
After installation
1) Mech installed CSB with flange the other way (which should be correct) and the driveshaft is now straight, but...
2) ...I now have a vibration around 60-75kmh that I can feel through my seat. Clunking is gone though.

We've tried adjusting the preload of the CSB back and forth and also the tightness of the clamping nut, but at best, the vibes are still there.
So now, is the CSB I got the wrong one? Should I go and get the slim bracket version instead?

[tonytony]

did you mark the drive shaft before you took it apart? It might be off balance now

[evilnickwong]

Yeap marked both ends before taking it apart. I did read that even one spline tooth out of the original position and it could affect the balance? It's possible that we lined up the marks by eye, but might be actually 1 or 2 splines off I guess.

[jlevie]

In almost all cases, a failure of the rubber mount of the CSB is the result of binding u-joints in the drive shaft. Replacement of both the CSB and drive shaft is required. You can replace only the CSB, but the new part will have a short life and there may be vibrations from the drive train from the binding u-joints.

[evilnickwong]

jlevie: I understand that from your similar reply on my other thread (the one about the diff mount), but there was zero vibrations previously with the same drive shaft, so I don't understand why with a new CSB, the vibrations appear.

[jlevie]

If the old CSB's rubber mount had failed, the drive shaft wasn't constrained like it is now. So binding u-joints may not have produced vibrations then that you could feel.

[evilnickwong]

Hmmm I suppose that makes sense too. A binding U-joint will feel rough/unsmooth throughout it's range of motion or at certain points?

I did ask my mechanic specifically about the U-joints, but he said they were OK. It'll be a pain to remove it again to inspect. :(