240D door lock issue only 2 doors

[Marcan82]

Hello everyone hope you all had a great summer and having a good fall so far.

A new issue arose with my 1978 240D with only the passenger front and rear locks not locking using the drivers master door lock. They will unlock if for example they are manually locked with engine running but both doors will not lock with either engine running and pushing down on drivers door lock or with engine off using key in lock cylinder in drivers door. There were a few loose vacuum connections underneath the passenger floor mat but those have been fixed with no change.

Engine shuts off almost immediately after turning ignition off so I’m not thinking there is a leak anywhere.

Point or note is when engine is turned off and i go to lock pass door using key it locks but with some springy resistance.

[Marcan82]

Edit: they will UNLOCK if they were manually locked ONCE ENGINE IS STARTED

[Diesel911]

On the driver's door is a switch that has vacuum in I believe in the middle and the 2 outside nipples go to right and left. In the Manual there is a test for that and there is an allowable vacuum leak off.

See post 6 for a vacuum diagram

https://www.benzworld.org/threads/1984-300d-vacuum-system-doors-locking-troubleshooting.3080863/

[Diesel911]

Not picking on you specifically but in the last 10 years I have noticed decreasing interest in people in looking into old threads for the information. In the link below Hunter went through the trouble to organize the better threads on some issues.

Frustrating for me is that there is a member that posted here and on benzworld.org that posted a step by step on trouble shooting the whole lock system. The frustrating part is ci cannot remember his member's name. And in fact, I cannot remember the symptoms I had when one of the door actuator diaphragms developed a leak and nor can I remember the symptoms when I had that driver's door 3 nipple switch go bad.

http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html

Later I just decided I was done with the vacuum door system and disconnected it and went all manual.

[Marcan82]

This is a great start thanks very much. I did have a search for old posts but was unable to find my symptoms.

[jsb357]

Originally Posted by Diesel911

Later I just decided I was done with the vacuum door system and disconnected it and went all manual.

THIS ^^^^

I did a ignition cylinder swap as well so now I one key for
the doors and trunk and one key for the ignition.

Just like American cars back in the 70's

[Shern]

Originally Posted by jsb357

THIS ^^^^

I did a ignition cylinder swap as well so now I one key for
the doors and trunk and one key for the ignition.

Just like American cars back in the 70's

Unless that was a personal preference, it’s pretty easy to re-key your ignition tumbler to match the doors.

[Shern]

You have a leak somewhere.

Do you have a MityVac or equivalent? If not, stop right here, buy one, and return to the thread. The vacuum system on these cars is elegant but troubleshooting without the correct diagnostic equipment is a fool’s errand.

The spring-y sensation in the passenger door is due in part to a spring connecting the vacuum actuator and the physical (keyed) door lock. That spring had actually broken on my 240 and prevented me from using the key on the passenger side entirely.

[tyl604]

Mityvac is the way to go. You will always need it if you keep the vehicle.