I'm the second owner of an 87' 300 SDL... I bought it 4 years ago with 69,000 on it and now have 122k on the odometer. It runs great, is immaculate in and out and the only thing I've had done to it is a few hundred in front end work when I bought it.

The problem?

It has developed a vibration above 42 mph. At first I thought it was drive train related, but now I think its something else. Under acceleration, the vibration comes in at 42 mph. When you release the pedal, the moment the car goes below 42 mph the ride smooths out. At 60 I lifted, put it in neutral and it vibrates until 42 and then it immediately smooths out... so I don't think its a drive train problem - apart from the rear-end anyway.

The vibration is a seat of the pants, from mid car back vibration. Nothing big, but noticeable. My Brother noticed it too, without my saying a word... "hey, you got a little vibration here."

I understand all the suspension contact points with the frame and body are dampened by rubber bushings - and with the car being 29 years old and never having been changed, could this be the problem?

Any help or comments, no matter how far fetched would be appreciated.

ETA - The last set of tires I had - Michelins with a 90,000 warranty - were toast in 33k miles. The wear was not out of the ordinary - like under inflated, over inflated, out of alignment - they just wore out that quick. I have brand new yokahama's on there now. It was doing this with the Michelins and now the Yokahamas, so I know its not tires and I had the alignment checked - everything is copacetic.

Thanks,
Mike

Carrier bearing?

I had the same issue with my last set of Michelins. 90K warranty, had broken bands, strange wear marks, and would develop "flat" spots if the car sat for more than 2-3 days. Changed them out with less than 20K on them, and now have over 30K on the Yokohamas that replaced them with not so much as a wobble.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Visual inspection of things is best. Could be tire related and that should be eliminated first probably. Do you remember if the vibration started as soon as you changed tires?

Although even if it did not is not conclusive. Easily an out of balance or defective tire. You pretty much have to get that out of the way other than a visual inspection showing something else first.

It was already happening. I was sure it was the tires that were guaranteed 90k, but only lasted 30k - no abnormal wear patterns, they just wore out.

New tires and it is still happening. The odd thing is that its not getting worse. I would have thought if it was the carrier bearing, the worse it wore out the worse the vibration or at least, a change in the mph the vibration appeared.

I am just looking for ideas that I might be able to take care of before going to my local shop.

mw:

Examine all components of the driveline:
flexdiscs fore and aft, centering bushings fore and aft, u-joint, and the center support (aka carrier) bearing and its rubber mounting.

Then proceed to the axle shafts and CV joints.

I'm pretty sure it is your drive shaft u-joint. They get a little notch worn in them that's difficult to see/feel by visual inspection. Been thru this with my 436k mile SDL.

You can test by putting a couple washers between one of center carrier bearing housing flange bolts and the car mount point to change the angle of the drive shaft at the u-joint. If the vibration changes or goes away you've found your issue. Have the u-joint replaced & shaft balanced. Ran me about $300.

Otherwise the list is long...OE motor mounts, trans mount, center carrier bearing & housing, flex disks, differential mounts, & of course axle shafts(pull & reverse R to L).

Since you've ruled out wheel stuff, and with your lower miles I think it is just the drive shaft (seat vibration) but all the power train rubber is probably going south.

P.S. buy good rubber like Lemforder, Phoenix, or dealer...knock offs like euro don't last.

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1986 300SDL 440,xxx