1984 Mercedes 300D turbo - trunk lock problems.
 

OK, the trunk lock is acting up again. Rarely, the trunk won't unlock and open when the engine is turned OFF. When this happens, I have to pull the cable release located under the rear seat (driver's side) to open the trunk. This afternoon, for some reason, the trunk will ONLY open when I pull the cable release. I sprayed the inside and outside of the trunk lock with a special lock lubricant I have which normally works....this time no joy.

There is a slow leak in the vacuum system which is affecting the door locks; I know I need to track it down and fix it....seems like there is never enough time. About 18 months ago, I replaced the trunk lock vacuum actuator...it is hard for me to believe it would fail so soon. Also, I managed source a BRAND NEW genuine MB truck lock.....perhaps I should install it?

Now, when I manually pull the upper lever/cable to the left (which is what the cable release does), the trunk lock opens immediately. Sans that, the trunk lock is remaining stubbornly LOCKED. Photos are attached...my finger is pointed to the cable that I can pull to the right which unlocks the trunk lock. All ideas and input are appreciated!

I managed to locate some of the trunk parts for the 1984 300D. First photo may be a new vacuum trunk lock actuator....although I'm not sure....I have two of them but am unsure if they are the truck lock vacuum actuator?

Second photo is the new genuine mercedes benz oem trunk lock. I'm thinking the problem may be either the vacuum trunk lock actuator OR the trunk lock or perhaps both?

I thought there were two key positions on the trunk lock

In position one the trunk lock be controlled
by the position of the vacuum rod.

And in the other position the vacuum rod position had no
ability to unlock the trunk so it would be key only.

This would be the "valet" setting.

It's that way on my SEC

Wow be thank full that you have the cable because it is only on the cars that have the security system.

I have no idea how the security system interfaces with the trunk lock operation, but you can test the vacuum actuator.

When I did that on a door lock actuator, I submerged the actuator in water, and I had a hose hooked to one of the nipples. If it bubbles you have a leak. If no bubbled hook the hose to the opposite nipple and repeat the test.

Also, a good time to test if you are getting vacuum to the actuator.

His car has the security system. It might work differently. Or if something in the security system is buggers it might prevent what you are speaking of.

Not you can see part of the security system in the OP's pictures.

See the text in the attached picture.

The trunk lock key slot is in the horizontal position. I've been able to open the trunk easily for the past six months or so... I'm going to take Diesel911's suggestion and use his idea of placing it under water then connect a hose to test for proper function.

I do know there is a vacuum leak somewhere in the system because the passenger door locks respond slowly when starting the car and when shutting the car off. So, obviously, I am going to need to check the entire vacuum system for proper function as well.

"you can deal with this OR you can deal with that!!"

https://www.youtube.com/watch?v=miC1VZ9UVCQ

thank goodness our cars don't look like a bread box on wheels!!

Concerning my post #2, photo #1 above, I cannot seem to link the part number on the package it came in with the part itself. It appears to be a type of door vacuum actuator....does anyone know for sure where this part goes on the car?

Hang on a min… There’s no such thing as a localized leak. Either your system has vacuum or it doesn’t.

How quickly does vacuum leak down?

Do the rest of your vacuum locks function?

When trying to open your trunk, have you ascertained whether you still have vacuum in the reservoir?

This same W123 vacuum diagram is posted somewhere in our threads. At this site someone cut the bottom off but you can still see the trunk vacuum actuator connections.

The vacuum line to the trunk runs along the passenger side of the trunk. Unless my memory is not working well.

When the trunk vacuum actuator is out, I believe you will find a part number on it.

An eBay seller has this as a part number 123 800 08 75. The question is if there is a different actuator for the one that has a security system.

On the door vacuum actuators there used to be a fix if the exterior boot was ripped.

https://www.pinterest.com/pin/832391943607541896/

Vid trouble shooting the vacuum system
https://www.youtube.com/watch?v=TkLAKd4zlgs

Post 16 has a pic of me testing a door actuator and other info.

http://www.peachparts.com/shopforum/diesel-discussion/322550-w123-door-lock-actuator-diaphragm-2.html

Thank you to everyone for your contributions; obviously I am going to need to devote a day or perhaps more to tracking down the vacuum issues. I drove the car around for awhile today and for some mysterious reason, the trunk lock began to work properly. It appears to be an on again, off again problem.

She's strange........and I like it!

https://www.youtube.com/watch?v=aoiu3RhQ3ZI