It started with the car not shutting off (1985 300TDT). No problem, I know about the stop lever. So I take it to an MB independent. They are a bit far from home and I have no easy way to drop the car off, and they are busy. I wait for it and they track it down to the door circuit. But it's getting late, and they might not be able to get parts to finish it that day. So they say they can block it and I can bring it back. What I'm really thinking is I imagine that it must be the master vacuum switch in the door and I will fix it myself.

So that's where I am at. I am not skilled enough to track down a vacuum leak that could be anywhere, but now that I have a better idea of where it is, I think I can handle it. I read the "Diesel Giant" page about replacing the part.

My questions, should I just go ahead and replace the master vacuum switch and see if that fixes it? I imagine it is a cheap part and probably due for a change.

Or should I try to track the problem down a bit further?

Do I need a mighty vac?

Thanks

Peter

Yes you do.

For the remaining questions..........it depends on your skills and your patience.

I PMed you something.
This might be a time to develop a new skill or you will have to dip into the bank account! The thing to do is to devide the job up into bite sized sections that are easy to chew on. Unless you trace the problem to something under the dash/doors it is more likely the shutoff problem is caused by the vacuum lines/hoses are under the hood.
The first thing to do is get a good strong light open the hood (engine cold) and carefully run your hand down all the hoses looking for cracked/disconnected hoses or connectors which are most often the cause of vacuum leaks.
This is the sticky on vacuum diagrams.
http://www.peachparts.com/shopforum/showthread.php?t=105297
If you can find the right diagram it is mostly connecting the vacuum gauge to a hose or connector and seeing if what is supposed to be happening is happening.
Connect the gauge to the Vacuum Pump (members where is the best place to connect it?) first. If the Vacuum Pump vacuum is OK (see the manual for minimum allowable vacuum pump reading) go to and remove the hose from the shutoff valve and connect the vacuum gauge to the hose and have someone turn the ignition off and observe the vacuum.
If what I PMed you dose not help post the results and the members will be able to advise
e.

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84 300D, 82 Volvo 244Gl Diesel

Definitely worth getting a MityVac. I have used mine a ton over the past few years, definitly worth the money I paid for it. And it will save you a bundle in mehcanics time. The door lock system is pretty easy to diagnose. You can test each door seperatly without pulling the door panels and see if it is leaking vac. Then you know which panels need to be removed. I guessing you have a actuator that is leaking.

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No. While nice to have, it's not essential. You can plug the individual vacuum consumers in the door lock system to isolate the problem. And it's very improbable that the master valve is the cause of your problem.

For someone who is not thoroughly familiar with troubleshooting a vacuum system.........and for someone who doesn't want to leave the engine running for hours.........a Mityvac is definitely essential.