Hi everyone,
I have a 1983 300D Turbo sedan which is in great shape except for a vacuum leak that I suspect. When I'm driving, there's a really noticeable droning sound, like what you'd think sitting in a prop commuter plane sounds like. The sound is only when I'm moving, not when I'm idle. I originally thought this might be a bearing problem, but I also noticed that my door locks don't work when the car is off, and the cruise control pulses the accelerator. I know that the door locks and the cruse work off vacuum so I figure that maybe my sound is also a vacuum leak. Also, does the vacuum do anything to the transmission? It clunks a little more than usual. Where are common places that I should for this leak? Is it a vacuum pump? Is this presumed vacuum problem pretty typical? I hate it when my car has awkward sounds so this really bothers me. Any advice would be really great. Thanks!!!

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

DieselHead: On the vibration/noise, first thing I'd check is the driveshaft support, that's what the description sounds like to me. The car has a 2 piece driveshaft, the bracket that holds up the "middle" joint has a rubber support, which can wear out and cause a noise like this. i don't connect the vacuum problem to the noise. The vacuum pump itself may be bad, which is common on high-mileage cars. Your cruise is electronic, not vacuum, at least if it's an MB factory cruise. i may be wrong on that, but I'm purty sure about it. Vacuum systems can be a problem. if the pump is bad, it can allow engine oil into the various vacuum operated systems and really compound the problems, the oil swells the rubber diaphrams and connecting hoses, causing further damage and failures. Is the engine still shutting off OK? Vacuum operates the shut-off, usually the first complaint is either the door lock system or the engine shut-off system. Yes, the transmission is about the same as a gasoline engine transmission. It has a vacuum modulator like a gas engine transmission, but uses an alternate scheme to get the vacuum "correct", so the transmission will work as though a gasoline engine is supplying the vacuum, instead of a vacuum pump on a Diesel engine. So a shorter version of this is "Yes, a vacuum problem can cause the harsh shifting".
Gilly

Check the replies to my post of 5/3/2001, Icesailor provided a really thorough method of checking for door lock leaks. The post was titled: "82 300TD A/C problem". About the droning noise, my car does that too on the highway, especially at speeds above 75 mph. It doesn't seem to get any worse over time so I assumed that this is a characteristic of the Diesel engine, although I've never asked anyone about it. Oh, to search for the post, just click on the globe(search) icon above.

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Dave
1995 C280
1999 Triumph Daytona 955I - my speed fix.
1982 300TD - Gone, but not forgotten.