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  #1  
Old 04-08-2009, 06:09 PM
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Hopefully, a simple door lock vacuum question

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

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Old 04-08-2009, 06:27 PM
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Which car?
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Old 04-08-2009, 06:40 PM
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Should have specified - '78 300D.
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Old 04-08-2009, 06:46 PM
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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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Old 04-08-2009, 07:37 PM
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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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Old 04-09-2009, 11:24 AM
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Quote:
Originally Posted by ichbineinekrous View Post
...Not too many people can even figure out how to open the fuel filler flap anyway.
I feel the same way.
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  #7  
Old 04-09-2009, 06:35 PM
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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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Hopefully, a simple door lock vacuum question-vacuumgauge.jpg  
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Old 04-11-2009, 01:08 PM
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When you move the plunger, it may lose vacuum briefly while between the two positions, but it should hold vacuum when in both the 'locked' and 'unlocked' positions.

I think you've found your problem.

While you have the valve out, can you put vacuum to the 'lock' and 'unlock' circuits (where they connect to the master valve)? They should hold vacuum indefinitely.

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