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Old 10-05-2001, 09:25 PM
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Vacuum Door Lock Operators

I have a 1977 240D which I bought new. It has been a great car.

The most trouble I have experienced has been with the vacuum door lock operators.

I have become proficient in replacing and/or repairing them.

My question: Is there a way to determine in which door the faulty operator is located before removing the trim, handle etc?

It would be a lot easier if I could avoid using the elimination method I have used to this point.

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Old 10-05-2001, 11:57 PM
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Join Date: Jan 2001
Location: California
Posts: 2,068
First, you want to make sure your vacuum problem is with the operators in the doors. Disconnect both vacuum lines that go to the gas cap lock. This will isolate the gas cap lock as well as the trunk lock. Wait for a while and see if the car holds vacuum. If so, then you're lucky - the leak isn't in a door lock operator.
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Old 10-06-2001, 02:05 AM
MikeTangas's Avatar
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Join Date: Apr 2000
Location: So. Cal
Posts: 4,430
The following holds true for 108's, but should still be close on newer models.

Where the vacuum lines and electrical enter the lower A post on the driver's side, you should find two "y" junctions. One set of lines yellow, the other black (yellow to unlock, black to lock). One leg of the "y" comes from the master valve, with one leg running across the under side of the dash and the last leg dropping down to the floor.

The leg that drops to the floor should be to the left rear door. You can disconnect those lines and attach your hand pump to check the actuator for the rear left rear door.

If you remove the glove box door and liner, you should be able to cut into both lines and check function of the right side. You can repair the cut with a short section of appropriate sized vacuum hose. You can also pull the trim cover off the passenger side "B" post and access the lines going to the right rear door to individually test that actuator.

If you opt to do the tests this way, be sure to isolate the vacuum reservior but taking it out of the equation. Any leaks will show up very quickly without the reservior (plus you can cycle the entire system in about 3-4 pumps).

Personally I opt to pull the interior door skins, seems like a lot less work that trying to dig out the "y" and cutting and splicing.
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

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