85 300SD Door Lock Problems

[85Piece]

Hi All,
I am having a problem with the door locks on my 85 300SD, as it is now I can only lock and unlock the doors using the trunk, and I have to push the rear door locks in manually. The front ones went simultaneously last winter, and I have just been kind of lazy.

Anyhow here's my problem, I got a vac tester and it seems the pump is good, but I can not for the life of me find this master door check valve which seems to go bad with these a lot. Can anyone tell me where this is located exactly?

Any other ideas of what I might try out as I am checking through this?
Any help would be appreciated!
Thanks
Jim

[Oracle12345]

Your may have a vacuum leak in your lines that run along the floor pan. Also you may have problems with the vacuum diaprhams that are inside the door. If they cant hold vacuum then they have to be replaced.

[Bcollia]

Common problems on these. My 81 300SD has this from time to time, just not annoying enough to chase vacuum lines...

[tyl604]

My experience on 81 300SD. The driver's rear stopped working. The vacuum actuator was broken and I replaced it for $20 - very easy after you remove the door skin. Now the passenger front must be done manually; suspect it is also a vacuum actuator but have not looked. Do not know where the master is located but one thread said that it was inside the driver's door.

[Phil]

I have never seen a check valve on my 83, I am not sure if they have them on the SDs, they maybe only on the Ds. If you connect your Mitty Vac tester to the line that connects to the pump and pump it up or pull a vacumn does it hold or leak out? If it leaks then I would look under the carpet in the front passanger side. Under the carpet is a channel that has all the hoses in it and many of the connections so you can start testing there to see what works.