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1979 300D. Just awoken after 28 years in storage. 6,000 original miles!
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11 Posts
Discussion Starter #1
Hi everybody- I need some help trying to narrow my search for the dreaded vacuum leak. The front and back locks on the driver's side lock and unlock just fine, but the passenger side locks only and will not go up/unlock. If I unlock the doors using the driver master and give the passenger lock a little lift assistance, it will go up/unlock. Seems like weak vacuum to unlock the passenger side locks. Any suggestions where I can narrow my search?
 

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1980 Mercedes 240D, 1988 Acura Legend Coupe 5MT
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13 Posts
Take off the door panels and check out the 4 rubber diaphragms that are part of the locking mechanism. Most of them on my 240D were cracked thus not holding vacuum pressure.
 

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Premium Member
99 SLK230 Kompressor, 5 Speed Manual
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1,117 Posts
Use an auxiliary vacuum source like a Mity-Vac to apply vac to the line that goes across from the drivers locks to the passenger side locks. If it doesn't hold vacuum, move to the line to the rear passenger door. If it STILL doesn't hold vacuum, move to the filler cap line. This should narrow down to which of the three diaphragms is leaking. I don't know how you can determine a leaking diaphragm by a visual inspection unless it happens to be smashed.

Logical thinking and an aux vac source will find your problem. If you need more clarification of the procedure, just let us know and we will walk you through it in more detail.

Hope this helps.
 

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Premium Member
1967 250 SL, 1965 300SE lang
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3,073 Posts
I can't find it but somewhere on the web there was a really good primer on how to deal with the vacuum system. DieselGiant has some stuff but not exactly what you need. Basically there is a "lock" vacuum circuit (yellow tube with red line) and an "unlock" vacuum circuit. At any given point in time if things are working correctly either "lock" or "unlock" will have vacuum. The lines for the doors are under the carpeting, starting from the driver's door down from the hinge, then running straight back and also across the front of the front seat bottoms across to the passenger side. If you take out the carpets you will see the tubes and the junctions. All of the actuators can be tested without taking off door panels.

You MUST get a mitivac or something like it.

Basically you connect a vacuum line to the mitivac and you apply vacuum, you should see the door (or trunk or gas tank) actuator move the latch. You can hit and miss until you figure out which line goes where.

Note that the junctions can also leak.

autohaus az has inexpensive replacement parts, much cheaper than diesel giant.

Note that the gas cap has a "lock" circuit only, and not an unlock. The rest have lock and unock. Gas cap unlocks by a spring when "lock" circuit is not vacuumed.
 
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