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Old 07-27-2006, 03:11 PM
DieselBone's Avatar
for the glory.....
Join Date: Dec 2004
Location: Mechanicsburg, Pennsylvania
Posts: 355
stupid vacuum problem is driving me nuts!

First off....

CAR: 83 wagon

PROBLEM: car looses vacuum when locks are in the un-locked position, therefor car does not shut off when the car is un-locked. When the doors are locked, car shuts off fine. I used to be able to lock and un-lock the car many times before I ran out of vacuum, now I am lucky if I can do it once. What the heck happened? I am at my wits end on the problem. One other thing, when this problem first started if the car was shut off and doors un-locked, there was a buzzing/humming noise coming from the dash that would go away when you locked the doors, very weird!!

-Randy Wakefield

1969 220D 4 speed (parts car)
1976 280C
1976 280S
1981 240D 4 speed (parts car)
1982 300D
1983 300TD (Ivory)
1983 300TD (gold)
1985 300TD (gray)
1987 190D 2.5
1970 280SEL (sold)
1977 240D 4 speed (sold)
1974 280 (rusted to death)
1927 Chevy 4 door sedan
1938 Chevy 2 door sedan
1950 Willys Jeepster
1955 Studebaker President 4 door
1977 Ford F250
1979 Glastron 17'
1948 John Deere A
1960 John Deere 2010
1979 Satoh S650G
2000 Bichon (Doby)
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Old 07-27-2006, 03:39 PM
rrgrassi's Avatar
mmmmmm Diesel...
Join Date: Jun 2006
Location: Royse City Tx
Posts: 4,872
Sounds like you have a leak somewhere. It's the finding it that is a real pain. I just ordered a manual from MBUSA. I hope it has a diagram with color coding so I can chase all the vacuum lines my self on my 300D. Darned A/C keeps splitting the difference with windshield vents and center vents when the 3rd button is pressed.

70's SPM #5608 Fairmont A-4 MOW car

06 VW Jetta TDI 210K miles

03 VW Golf TDI 5 speed 372K Miles

RIP--Lost in fire...82 300D 322K was My Daily Driver-On the search for a w126 now...

90 Dodge D250 5.9 Cummins/5 speed. 350K
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Old 07-27-2006, 04:02 PM
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
Randy, one of the diaphragms in the doors is leaking but only on the upstroke.

You'll need to connect a Mityvac to the supply to each door and figure out which door is the culprit.
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Old 07-27-2006, 05:47 PM
Posts: n/a
I agree, here are a few more hints. The vacuum lines that control the "unlock" function are yellow with a green stripe. The yellow/red lines control the lock position. The yellow/green lines start in the drivers door and go to the other door locks. They travel under the front floor matts within black plastic "covers." The easiest way to test the system is to use the "Mityvac" to check the various portions of the system at the rubber tees located in these lines. When you find the section that will not hold a vacuum, you have found the leak. Do a search on vacuum leak and you will find lots of info.
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Old 07-27-2006, 10:33 PM
1984 300d
Join Date: Apr 2006
Location: Austin, TX
Posts: 102
Replace the short lines

I have had the same issues. In running the problem down, I replaced the short flexable lines that connect the hard plastic ones to the valves. The stuff is cheap ($1.25/ft) and the original does not last forever. As you go through testing various lines, just replace the ones that you touch. Replace everything under the hood (simple) as these are very likely to be loosing vac. I had some of the under hood rubber connections that were falling apart. A few of the interior ones were questionable. A little preventative maintenance can really help out. There are many choices as to replacements, I choose a 3.5mm ID silicon that is good to a very high temp (not good for fuel).
Mercury is a boxer

1984 300d
1999 Prelude
Medici road bike
Klein touring bike
Klein mtn bike
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