Our 1983D-turbo went in for a problem with motor-boating and draining the battery due to incomplete disconnect. The key switch had been replaced but they claimed the mechanical part was worn out. It took them 2 tries to get the right mechanical piece - then they said the vacuum pump was under-performing and needed replacement.

Our garage says they've tried 3 aftermarket vacuum pumps and they're all too weak.

Mercedes is quoting them over $400. for one.

My guess is that they are missing something like a gasket or leak or something.

I read elsewhere here that there is a vacuum switch on the ignition switch and a vacuum actuator elsewhere - are they blaming the pump rather than the correct cause?

Thanks!

Hmmmm....sounds more like a failed mechanic than anything else.

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Sounds likely. It's relatively easy to check the vacuum output at the pump - just disconnect the output tube, install a vacuum gage (most turbo boost gages will have a vacuum side as well as a pressure side and they're cheap at Harbor Freight) and actually measure the vacuum with the engine running. Not sure how much is enough but someone on here will know.

Yep, I'd go looking for a leak. If you have a friend who vapes you can have them blow a cloud in the area in question (say, near the ignition switch) and see if the "smoke" gets drawn into the questionable area. It points up vacuum leaks pretty well.

Dan

Thanks for the quick replies!
I've been searching the Net for more info but can't find one number.
Some good data for our 1983 W123 300d here:
https://www.ifixit.com/Device/Mercedes_W123
and here
https://**************.com/problems/vacuum/determining-correct-1980-1985-diesel-vacuum-system-hose-and-line-routing
But ...
Anyone know what vacuum level indicates a properly working pump, please?
If I'm to move the garage off stuck at the pump I need to get them that number.
Thanks!

It sounds like their thinking is even with numerous vacuum leaks, such as door locks, climate control, fuel shut off and ignition switch, if you throw enough vacuum at it the problem will resolve itself. And it may...temporarily.

Have they checked the fuel shut off with a hand vacuum pump? Have they bypassed the climate control or door locks to see if it shuts down?

Thanks - I will forward those tests to them.

I recall I usually see ~16"Hg vacuum when my 300D vac pumps are working well w/ no leaks anywhere. If they haven't checked the vacuum right at the main tube, with nothing else connected, then they are idiots to be blaming the vacuum pump and you should vacate that shop and never return. Not saying they are, you need them to explain exactly how they tested.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans