Hello All,

I recently did some major part replacement including:

New rear axles
New rear subframe mounts and trail arm bushings
New shocks
New sway bar links
New flex discs and Center bushing along with new guide bushings on the ends of driveshaft
New transmission mount
New rear diff mount
New motor mounts

After all was put back together the car mysteriously vibrates badly starting at around 42 mph.

I marked the driveshaft in the center and in relation to the rear diff and transmission, so that is not the issue.

I have tried loosening the Center carrier mount bolts and rolling the car to seat the shaft. That didn’t help.

I jacked up the rear and ran the car in drive and could hear the vibes start but couldn’t see any abnormal vibration looking under it, although the rear passenger side wheel did not turn as freely as the drivers side but I think that is a dragging brake caliper issue.

The vibrations occur in all the driving gears, but do not occur in park or neutral.

I’m pretty well stumped as to what to do next so I’d appreciate any fresh perspectives or similar experiences and general advise by the members.

Thanks in advance,

Marc
1981 w123 300D

When you tightened the 46mm DS nut followed by the center bearing mount, was the car still on all 4 wheels? If not, this can make a difference. Aligning the DS to the transmission or differential should not make any difference.

Did you install the axle spacers left to left and right to right? This is crucial.

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Don't Chrome them; polish them

Hi,

As far as the axle spacers go, the left side from the old axle fit. On the right side the original spacer was too thick to get the circlip in place so I ordered a thinner one from the dealer and it went on and had no play that I could see.

I didn’t do anything to the DS nut up in removal or replacement. Maybe that could be my problem. I need to go find a 46mm wrench and try that.

Is it odd that I didn’t need to loosen that when I dropped the DS?

Thanks!

If you didn´t have to loosen the DS nut for removal, then it was loose enough to collapse the two haves (but it should be tight). You say you replaced the center bushing, I assume you mean the center bearing carrier/mount (hopefully the bearing as well), so the two DS halves had to be separated to do this. Did you match the alignment of the two halves at reassembly?

Once the DS is mounted, the center nut must be tightened so the two halves can not slide. The center carrier is mounted but not tight. Tightening it is the last step. So when the car is rolled for setting, the nut and center bearing carrier must be loose just enough to seat before tightening.

After car is rolled, or rear of car bounced up and down - while on all 4 wheels - tighten first the nut, then center bearing carrier. It's important that all this be done with the car supported on all 4 wheels.

If you run the engine and DS with the car off its wheels, it's best to raise the rear trailing arms to avoid stress on the axle ball bearings at the full down position.

__________________

Don't Chrome them; polish them

Hi Marc,

I had a similar experience with a 1982 240D with manual transmission. The problem turned out to be the collar on the back of the transmission that mates to the flex disc had rounded out bolt holes. The problem was spotted by an employee of a local shop with a sharp eye and a keen sense of how things should look. They replaced the collar with a used piece they had on hand. No problems since.

Marvin Kraft
Green Valley, AZ

The universal joint could be bad. Did you check it while on the car?

Markmaru did you remove the large nut inside the final drive flange at any time ?The part that the prop shaft or driveshaft and the coupling fit to .