hey guys....
got another problem. front passenger door wont lock at all, the lock will always stay up. I can force the lock to go down but it will pop back up with force. I tried to strace the vacuum lines from the vacuum pump to see if i have oil in the vacuum system because i was told that oil would complicate stuff. I did find a little bit of oil but it was located in one of the stop valves ( small blue cylinders branching off from the main vacuum hose that connects the the brake master cylinder). There are 2 of these valves, one of them are ok, but the other when i pull it out shows a little oil on the tip of the connector and also releases some vacuum from the system. when i removed the line from this stop valve, it seemed like air was coming out of it. I then tried to lock the doors and then the front passenger door lock when down.

do i need to replace this valve or is there something else that i need to check on. Also will i have any performance problems such as the A/C system malfunctioning...and ect..

your comments are greatly appreciated

The door locks on a '78 are operated from a swith on the driver's door -- the yellow plastic line goes to the vacuum swith there, and the lock/unlock lines (yellow with red stripe and yellow with green stripe) go from the driver's door to the vacuum elements in the doors, the trunk latch, and the gas filler door.

It sounds as if you have vacuum applied to the passenger door element all the time, or that one of the lines is plugged.

You will have to remove the door liner to get to the locking element -- pull the lines off and use a mitiVac hand pump to test. If it doesn't work, replace it.

You can also check the operation of the system with the mitivac by connecting it in the engine compartment and manually pumping down the door lock system.

My guess is that you have oil or dirt (or bits of a failed check valve) in the locking system -- if you have oil, the vacuum pump diaphram is bad and you need to replace it, and clean out all the vacuum lines.

The little blue thing is a check valve so that the system doesn't leak down when the engine is off -- you can replace it with any similar check valve if you don't want to spend the money on the MB part.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!