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1985 300D Vacuum Check Valve

Hello, I am currently learning the vacuum system in this beast while I am trying to fix this problem. The problem is the locks don't work at all and I have to manually shut off the engine from under the hood. However, I feel I am making some progress. When I remove the vacuum check valve (yellow thing with one tube going in and two grey tubes going out) and plug that one hole then the engine shuts off just fine. So I figure the problem is either this check valve or something beyond that point. Before I start checking beyond this point I am hoping to check this check valve. When I blow or suck through either of the two grey ends my breath flows freely in one grey hole and out the other (No breath goes through to the yellow end). I cannot blow or suck through the yellow end at all. It is because of this that I think this check valve might be the problem. Can anyone confirm that I am on the right track or perhaps tell me how I can check this part? It is difficult for me to go out to get parts due to time issues so I hope to purchase the correct part the first to time to the shop.

Reply to
cablet
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Your car most likely has a vacuum leak in one of the door locks, fuel filler or trunk lock. All are vacuum powered as is the engine shut down. A leaking door lock actuator will cause all of the symptoms in your car.

Reply to
T.G. Lambach

I have an '82 123 300D. And I have the manuels on CD and paper. If your car is the same, I could look it up for you. I've been through that system extensively, although a few years ago. Hasn't broken recently.

Larry In the back yard, under the oak.

Reply to
Central Florida

If I understand correctly, you plugged the one line from the pump. Did you try plugging just one of the gray lines, then the other? I think that check valve is a one-way flow.

Like TG says, most likely a door lock element gone bad. Or the vac hose running to the drivers door, at the hinge. The easiest place to check that stuff is in the passengers foot well, under the carpet. After unsnapping the carpet, remove the couple of screws that hold the cover plate. Under that is where all the connections to the doors, fuel flap, trunk lid, etc. are located. Each element has a lock side and an unlock side. In other words, vacuum must be applied to one side of the element to lock the door and vacuum must be applied to the other side of the element to unlock the door. You will need a hand held vacuum pump (thirty bucks at the local parts store), a couple of golf tees and some time. Unplug each element's pair of lines. You will be able to tell the pairs of vac lines by their color/stripe code. Apply vacuum to each line. That will lock and unlock each door. If (or when) you find an element that doesn't respond, plug that line. Then start the car and see if that was the only leak. If it was, the car should shut off. Depending upon which element is bad will determine the complexity of your next lesson in the art of car care.

Larry In the back yard, under the oak.

Reply to
Central Florida

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