The locking mechanism had a vacuum leak on my 85 300td. I disconnected the door locking system under the hood and plugged the line a few months ago, now I'm trying to troubleshoot it. All the door pod mechanisms, including tailgate and fuel door test fine both opening and closing. On the switching valve on the drivers door there are three lines. I can pull a vacuum on the rear one and it locks all the doors. I can pull a vacuum on the center line but nothing happens. The center line holds vacuum. I can't pull a vacuum on the front hose to the switching valve. I also can't pull a vacuum on the hose going to the system from under the hood.
Is there any one with wisdom as to what is happening? I assume this means that there must be a leak somewhere between the line under the hood and the driver's door switching mechanisms. But, I'm assuming the center line on the switching valve is the unlocking line. Why won't the doors unlock when I pull a vacuum on that line? What am I missing here?

EDIT:
Now I'm more confused. I can still pull a vacuum on the rear most line of the driver's door switching valve but nothing happens. I've also looked at the sticky vacuum diagram and now know the middle line is the line from the vacuum pump. It still holds a vacuum so I know the line from under the hood to the driver's switch is good.
So, I'm concluding that my problem is a leaky unlocking line somewhere. Any hints as to where it might be? Where should I tap into the unlocking line downstream to test it?
But there is still the oddity as to why the doors wont lock when I pull a vacuum on the rear line at the driver's door switch. I also locked the driver's door and then pulled a vacuum on the system from under the hood at the locking mechanism line. I assumed this should lock the doors since the unlocking line should be excluded from the system by reason of the driver's door being locked. I could only get 10 inches of vacuum there (as opposed to 24(?) when I tapped into the locking line directly at the driver's door switch?
Any ideas? My mind is a vacuum.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

TTT

ANyone have any ideas? I replaced the valve on the drivers's door. (by the way--the dealer says there is a new valve for that location--$51. I bought the old version for $18).
The unlock system won't hold vacuum so I know I have a leak there somewhere. But the locking side is still holding vacuum but non of the doors lock. Does anyone have any idea why this would be happening. They worked fine before the whole problem arose and they worked once when I pulled a vacuum on the locking hose on the driver's door switch. But now nothing happens either with a mity vac or with the system vacuum.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Kerry - have you looked at the vacuum diaphragms for your particular model. They are "stuck" at the top of the diesel forum.

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Jim

I think the next "junction" down the line is in a plastic tray under the passenger floor mat. Should be a couple rubber 4-ways under there

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This Space For Rent
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Yes, I looked at the diagrams after my initial explorations so now have a rough idea of where the lines run.
I tested each of the diaphragms at each door and all worked fine isolated from the system.
The leak in the unlock side seems to be just a matter of tracing down a leaking connector somewhere.
But, for the life of me, I can't figure out why the doors aren't locking. There's no indication of any leaks anywhere on the locking side and it holds both with the system hooked up (car shuts off fine when in the locked mode) and holds vacuum with the mity vac but no movement at all on any of the locks.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

try using the mity vac on each door actuators. the rubber boot that seals the unlock side of the actuator diaphragm around the actuator shaft ALWAYS splits and leaks away your vacuum. as far as the locking problem, it sounds like you have a massive leak on the locking vacuum line either going across the floor to the passenger side of toward the back on the gas door/trunk line.

... double check that you don't have any lines crossed at the driver door switch.

Could be a kinked hard line- holds vac yet it cant pull the actuators, try opening and closing the dooes with the mityvac hooked up.

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This Space For Rent
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http://www.**************.com/store/item.php?item=123%20Vacuum%20Door%20Lock%20Advanced%20Troubleshooting%20and%20Repair

try this site for some good parts and troubleshooting info. It helped me fix my llocks.