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Humming vibrations from rear over 80 kmh

Started by Berggreen, 21 November 2022, 01:45 AM

Berggreen

Hello All

I have excessive humming-type vibrations from the rear which set in at exactly 80 kmh and remain upwards in speed. The car is a 12/1977 350SE.

The story is that I sent the car to my regular Mercedes workshop to have the center bearing on the propeller shaft replaced along with the flex disk.

After I picked up the car the vibration problem appeared (no vibrations before that), and it went back to the shop, where they insured me that the shaft had been marked up before disassembly. As the old center bearing was damaged during disassembly we could not reinstall it, but we reinstalled the old flex disk which was actually ok. But no difference - the vibrations were still there. They also rotated the propeller shaft in many other different positions to try to trouble-shoot and even tried to mount a different propeller shaft from a 280SE, also in the workshop at the same time, but again no difference!

They then removed the drive shafts to the rear wheels, and with the car on the lift the vibrations disappeared. They identified that the heads on the drive shafts had tight regions of movement and the bellows seems to have leaked grease, and what came out looked thin and oily. So they took the shafts apart and cleaned everything, added new grease and mounted new rubber bellows. Still the shafts had some regions of slight tightness, but they went ahead annd installed them. Unfortunate, it did not make any difference. The humming vibrations are still there and completely unchanged, even when they rotated the drive shafts from left to right. So they sort of gave up on the idea that the drive shafts were the source of the vibrations. (What do you think?)

Finally, as the old differential had symptoms of wear and was noisy, so one with lower kms was installed, which removed the wear noises, but again the vibrations are still there over 80 kmh!!!

We are now totally frustrated and going out of our mind and have no more clues what to do. :o

Have any of you experienced something like this or do you have any good suggestions what to try next?

Thanks,

Christian
02/1971 MB 280SL (aut.) - olive green 291H
11/1970 MB 280SL (man.) - silver 180G
12/1977 MB 350SE (aut.) - deep green 825H
03/1969 Volvo 1800S (man.) - dark green 94

ProfessorExperimental

#1
Checked you haven't lost a wheel balance weight?
Checked your wheel bearings?

Now accepting the premise that it's something the workshop did: sure, they marked the prop shaft, but did the same bolts go back in the same holes? I marked my RX7 propshaft to the diff when I rebuilt the diff, but that doesn't mean I bolted it up exactly as it was... My vibes only set in at 170 though so I CBF chasing it.

[Edit] while trying to help fichtl with the helper springs issue I just noticed on the parts diagram that there's a centring sleeve inside the end of some versions of the prop shaft... Yours maybe? Check Niemöller to see what I mean... https://www.niemoeller.de/en/w116/w116-mercedes-280SE/B024/410101 part 22
-Mark

rumb

Have the driveshaft balanced. Also the big nut that locks the 2 parts together must be tightened with the suspension loaded, not with wheels hanging.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS