I have been doing some troubleshooting, trying to isolate a slow leak. If I lock the doors after driving the car, all 4 door locks lock appropriately, and if I try and unlock them within a few minutes they will all unlock. But, if I wait a while (1/2 hour or so), then they don't unlock anymore.

I have been checking hoses with my Mityvac and have found a slow leak in the plain, yellow hose that runs from the check valve under the hood to the front driver's door (at least, I think that's where it runs). The reservoir hose holds vacuum just fine and so do the rubber door diaphragms.

What does this leak indicate?

ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

Which car?

Should have specified - '78 300D.

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

The 3-way valve in the driver's door. Its called the master switch or something like that, but its a 3-way valve.

If your doors are locked, then that solid yellow line goes to the 3-way valve, and then out that valve to the yellow/red lines. So if you checked all your yellow/red lines that lead to the other doors, then the 3-way valve is leaking. If the doors are unlocked, then the above is true for the yellow/green lines.

To check the 3-way valve without taking the door panel off, pull up the drivers carpet and get to the vacuum lines. Pull the yellow/red line that leads to the valve in the drivers door, and plug it. Lock the drivers door and draw a vacuum on the solid yellow line under the hood (or plug that one and pull the vacuum on the yellow/red line, whichever you want). Repeat for the yellow/green line with the door unlocked.

If its not that, it could be any of those black rubber connectors.

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now

I would recommend pulling all the carpet and mats and exposing as much of the vacuum system as possible, pick a nice sunny day with no interruptions and go to it. My issue was the vac. reservoir, which I patched at the inlet with silicone, and the fuel door lock pod. Not sure if yr 78 has the fuel door pod. I just plugged it and took it out of the loop. Not too many people can even figure out how to open the fuel filler flap anyway.

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1985 300D Gretchen (Astral Silver) 220k
1983 240D 4-speed Evelyn (Orient Red) 203k


TANSTAAFL

I feel the same way.

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now

Continuing to do some troubleshooting on my locks. I went ahead and pulled the driver's side door panel and pulled out the 3-way master valve (I kept getting a slow leak when applying vacuum to the plain yellow hose in the engine area).

I can't find any leaks anywhere else so I am testing the valve as shown in the attached picture. I am applying vacuum to the center port (where the yellow hose connects from under the hood) and am plugging the ports for the yellow/red and yellow/green hoses. The plunger is all the way depressed inside the valve (if you pull the plunger out of the valve to the left, then you immediately lose vacuum) and I applied 13 inches of vacuum. After 30 minutes the vacuum has leaked down to 5 inches...

I am thinking that this is my problem and that this valve should hold vacuum indefinitely (maybe), but definitely longer than 30-45 minutes.

Looking for some confirmation - does this sound right? Shouldn't this valve hold vacuum for a while?

ryan

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__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE