This is my second problem with this car, first one is intermittent stalling, that has me searching for expert help. I get these two fixed and I am one happy man. Again, 1972 350SL with 130,000 miles. I have had a vibration on acceleration and at certain speeds, not necessarily RPM. Mostly between 40 and 65 MPH and more obvious when more torque is applied. I have targeted the driveline as the problem, but could there be something else? I have replaced rear transmission mount, driveline flex couplers and entire driveline (new and balanced). Vibration still there. Question: should there be some end play between driveline ends and transmission/differential connectors? Do you entend driveline until tight and seated in recesses at connection points? Is there a proper sequence (ends first, center bearing next, etc)?

What about your motor mounts? Just a thought. You have checked and done everything I would think of, I would however install new motor mounts, and loosen the trans rear mount, and the exhaust hangers that connect to the tranny, start the engine and let it warm to operating temp so that the engine settles and the exhaust expands. Then go in and retighten everything up to ensure it is positioned well. Is the vibration coming from the rear? What about your half shafts? Have you checked those, sometimes when it is a noise or vibration during acceleration one would think the rear end, if it quits when you let off the gas? Does it seem like a balance vibration or a mechanical vibration? Remember these cars are really tight, vibrations and noises travel really well, I had a humming in my S 140 once, could not find it, finally had to take it to an expert at the dealership, it was the drivers rear bearing, It sounded like it was everywhere in the car. Good luck!
Brian

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Brian W. Heitman

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Thank you very much. Great advice. I can look at these since it doesn't seem to be in the driveline. Thanks again,

I would have to say it is a mechanical vibration. Just does not seem like a tire. wheel thing. The vibration is a loping, surging type, sort of harmonic going up and down. This is on accelleration and especially with load. I feel it mostly if not completely in the steering wheel. Don't feel it in the seat or dashboard when I lay my hand on it. Does not seem to be coming from the rear end. Starts in at around 2000 rpms @ 40 mph and continues up to around 70mph. Above 70 feels good. Letting off the gas helps , but not completely. Haven't tried your other suggestions , but thought better information may help.

Sounds to me like it could be your rear end differential. In the case where vibration or noise (humming) occurs that is of the mechanical type that is strong during acceleration under load, and then lessens when you let your foot off the gas usually means that the differential is experiencing some problems. Have you checked the fluid or changed it according to maintenance intervals? The one thing that throws me off though is you feel it in your steering wheel, that could be unrelated, does the vibration in the steering stop when you let off the gas as well, as I said the solid build of these cars makes it very hard to find problems sometimes. Take a look at your records regarding the differential, see if it is leaking, leaking can cause the differential mounts to fail, if no problems found call the dealer and ask if you can get an appointment with a specialist, drive the car with him in it and describe the problem, this cost me about $99 bucks, but well worth it as I was told exactly what was wrong, very hard to diagnose over typing. Good luck!
Brian

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Brian W. Heitman

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Thanks again Brian. I will probably end up doing just that. I did have the rear end seals replaced just a couple of months ago. They had to tear it all apart so should be okay. One would think if mounts are bad they would have been noticed then. If I get it fixed I'll post the cure.

Doug Spray