Car-77 240d

I just replaced my driveshaft center bearing. I didn't drop the whole shaft, just pulled the back half off to replace the bearing. Anyways, I just looked at a write-up here which says the "shoulder" on the center support bushing must face the rear of the car. I believe I put mine on backwards (the old one was destroyed and i didn't notice any mention of this in Haynes). Could this cause a vibration? I have a vibration that starts around 40-45, reduces as I climb up to 70mph, but never completely goes away.

It is also possible that the shaft is not properly re-alligned. I have already seperated it and repositioned it once. This did reduce vibration. I did mark it, but the splines are small and the markings far apart. I was going to try moving the shaft over two splines in the opposite direction of the last adjustment, but first would like to know if this bearing mishap could be the problem.

Also, can flex disc orientation cause vibration? It would seem to me that if the flex discs are replacable, they should be balanced themselves (otherwise installing a new flex disc would require re-balancing)

Any input would be greatly appreciated. This is my only car and I really need to be able to drive it as soon as possible.

Also, I did inspect the U-joint and it is nice and tight, so I doubt this is the source of vibration. I never had vibration before, even when the bushing for the center bearing was completely torn up and doing nothing to support the shaft.

failing old flex couplings will certainly cause vibration and shuddering. when you install the center bearing do push the car forward and back a couple of times to center the drive shaft the tighten the big nut .if you did it jacked up then it it misalign when on ground.
flex coupling has a k marking for the clutch side.

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mark

Thanks Mak,

unfortunately I went to turn the bearing around and punched in the cover or the race... it became sticky. I took a close look at the back flex disc again, as I could see small cracks while i tapped it with a hammer to push the driveshaft forward, and decided that they should just both be replaced. I lost all patience and decided that I wanted this job done right.

Got her loaded on a flatbed and brought to a reputable mechanic (my uncle has used him for many years) with plenty of old MB's in the lot. Today's lesson was to know when to give up and hand it over to a professional.

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Old Blue-'77 240D just rolled 111111 miles...
with the recently repaired odometer

The two piece shaft is balanced at the factory as one piece, so you might have to take it to a driveshaft shop and have it balanced again.

Also there are small balancing weights on the shaft that are small square pieces of metal. They are only superglued on and are easy to knock off when you are working on the shaft. If you lost one of those you will never get the vibration out without having the shaft balanced.

I had a vibration at low speed which was a too tight rear U-joint once. I soak the rear joint in a coffee can of oil now. It must be free to wiggle and the rear sleeve rubber inside the rear hanging support arm must be good.

I doubt your mechanic has a machine to balance the drive shaft, so he will have to send it out after replacing the center support bushing. Your vibration is most likely from the misaligned DS halves although vibration can also come from not replacing the DS yoke in the original position to the differential and transmission yokes; the DS is originally balanced at the factory on the car. Worn flex discs can also cause vibration but since you say there was no vibration before you started this project, that's probably not the reason. Even though the center support bushing was on backwards, that's not likely the cause of the vibration either.

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