I have an '81 300 SD that gives off a rather harsh vibration while accelerating. You really feel it between 15 and 25 mph coming up through the floorboard and gas pedal. I was told by a Mercedes mechanic that it was a bad universal joint. It did remind me a lot of a similar problem in a BMW 325 which was indeed remedied with the installation of a new (rebuilt) driveshaft. I pulled the Mercedes driveshaft out and there seemed to be a notching effect in the universal -- that is, it would pop into a home base position which was straight ahead on both sides. Oh dear, one rebuilt driveshaft later, I still have the problem. I'm hoping it's not the tranny which seems pretty smooth all in all. Could it possibly be a bad torque converter? I have so little experience with automatics that I'm just guessing. I throw myself at the mercy of Mercedes master minds.

Ask yourself this question. "Why does the noise come on at 15 and go away at 25". Is it because the transmision shifted into 2nd at 15 and 3rd at 25, then you likely have a transmission problem.

If you still have the driveshaft out start the car put it in gear and rev the engine SLOWLY from 0-40 mph see if there is any noise. This will require very little throttle without a drive shaft. Also note the RPM vibration occures at. DO NOT PUT THE CAR IN PARK UNTIL AFTER YOU SHUT OFF THE ENGINE or you will hear the load noise of a parking pawl trying to engadeg into a rotating parking plate. If you get vibration doing this test you have pretty much isolated the problem to the transmission. If you dont get vibration you have not yet eliminated the transmission.

If you already have the drive shaft in the car try a road test using full throttle acceleration and followed by another using very light acceleration. This will cause the transmission to shift at different points. If the problem occures at the same speed all the time no matter what gear your in you have now isolated the problem to be something that follows wheel speed only. That would include somewhere from the output shaft of the transmision (unlikely) to the tires (somewhat likely, more likely if the problem occered at about 50 mph).

Problems that are agrevated with speed and keep getting worse as speed increase are generally accociated with pure imbalance. Problems that get aggravated within a certain speed range are generally accociated with system stability issues and may be highly aggrevated with imbalance. It is unlikely the problem is in your wheels because the typical wheel and tire combination has dynamic stability issues in the 50 mph range. You appear to be well below that speed. But if the radail plys break down in the tire side walls the dynamics could change.

The drive shaft on the other hand should have stability issues at a speed faster than the car can go unless something happened. Something that would change the drive shaft stability would be its mounting or a crack, and infact the transmission, engine and differential mounts could also come into play. The most likely components supporting the drive shaft that have been known to degrade are the drivechaft center bearing support or the rubber flex couplings.

You may want to put the car up on jack stands and run it. If the problem will occure on the stands take a look at the wheels to see if they are obviously bouncing up and down. If not remove the wheels and install 3 standard bolts on each wheel to hold the rotors firmly in place. Run it again and see if you still have a problem.

I will give you what I consider my most likely guess. And that is that your problem is most likely in the driveshaft center bearing support.

John Roncallo

Sorry, have owned a tranny shop for 15 yrs.

Tranny's "DON"T" vibrate, never have seen one it will always be the shaft or mounts, etc:

JKohn1

Guess what, I have a 84 500SEL, 91 300D, and a friend has an 87 420SEL and another friend has an 88(?) 300E, and all have the exact same problem. Same speed, only when accelerating, and 1st or 2nd gear. I have learned to accept it as normal. If someone comes up with a fix, I would love to hear about it. By the way, my 84 500SEL has all new engine, trans, differential mounts, new flex disk and new center support mount and bearing, and rebuilt driveshaft.

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84 500 SEL (307,xxx miles)

Is the vibration totally dependent on speed or is it also dependent on load?

Don't forget the drive axles. They are very susceptible to vibration under load from the CV joints if worn.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

same thing on mine... problem was that one of the pistons/cylinders wasn't being compressed correctly/enough. fixed now and runs smooth

Many cars with 2-piece drive shafts and center support bearings have drive shaft vibration issues. Other than the above mentioned things to look at also look at things like the bushings that hold the diff. including the one right at the front. also look at the sub-frame bushings. Every thing from the front of the car to the back needs to be attached nice and firmly and in a straight line. I've seen people have a-little luck fixing minor drive shaft vibrations by shimming the trans mount up or down or the front of the diff. up or down but never tried that myself.

I have had the problem at about 40 mph. I started expermenting and on my car (the 84 500SEL) raising the rear of the tramsmission about 3/16" made it almost go away. You can also try lowering the center support by using washers, and changing the angle of the diff using washers. The center support and diff tricks didn't help mine at all, but it didn't hurt it any either, so they both went back to original. There is a procedure to allign the drive line but it requires special tools which I have never been able to find anywhere. Even the local dealer said they didn't have them. They just said to replace all mounts from front to rear and install a new driveshaft and that would fix the problem. I didn't wait for them to give me an estimate.

Paul

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84 500 SEL (307,xxx miles)

Over the years I think I've done just about all the above; motor and tranny mounts (several), flex discs (several), shimming the center bearing support, subframe bushings, diff mount, ad nauseum.

One thing that is interesting; it absolutely does not do it until the car is fully warmed up. For the first 5-10 miles, it doesn't have a hint of the vibration, even under pretty hard throttle. But, after the entire driveline gets good and warm, it begind to vibrate under acceleration, and seems to get a bit worse the hotter everything gets. I thought masybe an expanding driveshaft was binding a bit, but after lubing and torqueing my center DS slip joint, it moves forward/rear quite easily, even with the big nut properly torqued - so can't be that.

DG