Howdy folks,

Just getting back into the world of MB diesels, I just picked up a '78 240d that needs basic maintenance but otherwise a decent rig.

This is my 1st MB with 123 chassis....longtime 115 person previously. I've never had to deal with the vacuum door lock system. This 240 has an issue, the driver side/driver side rear door will lock by hand when inside/doors closed....but the passenger side doors won't lock....if I push the front one down there's resistance and it actually will push up the rear door lock, then if I push the rear door lock down it pushes up the front one! It's comical really.

Anyway I have a digram of the system and will eventually buy a Mityvac tester so I can go through and repair the system but in the meantime...I just want to lock the doors.

In looking at the diagram and reading posts I deduced that I could unplug the vac going to the yellow tubes that feed the door systems, plug the other end up , and it should be good to go, right?

Well I didi this, and nothing happened ! So I'm kind of stumped, maybe I'm missing something? I tried to upload a photo of my connection setup in the engine bay by the firewall but it said "upload failed" for some reason.

thanks,

Mk

Can you key lock the passenger door? If the door is in the locked position, you’ll still have resistance.

Seems like you may have an issue with the master actuator located in the drivers side door.
If you remove the line in from engine side you still have (from memory) two check valves to contend with, and possibly, a closed system. If you want to vent the whole system, look for the Y connector in the passenger side foot well. Tbh though, messing with this system at all is a fool’s errand without a mity vac…

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1981 240D 4sp manual. Ivory White.