1972 300SEL vacuum doorlocks R.I.P!

[silverbenz]

I've read that the automatic vacuum doorlocks never work on old mercedes, and I thought, "cool, mine work, I've got the last one"..
until today. With key, I could unlock the driver door, and the other locks
would slowly rise also. The same when locking.
Today, only the drivers door lock opens/closes with the key, and the other three doors are stuck in the unlocked position; I can't even lock them manually.
I've read a thread about a vaccum pump, can anybody tell me where it is? Also another thread said to block off the manifold lines with golf tees
leading to the vacuum lock system, and just use them manually.
I'd rather have my auto system back. My manuals have no sections
on the lock systems.
any tips from the cyber-garages?
Thank you again,
-Baron von Krieg 1972 300SEL 4.5L V8

[cth350]

no vacuum pump on these babies, it's strictly engine vacuum.

The system can work well, but after 35 years or so, the vacuum diphragms, being rubber start to decay. You need to fix them door by door.

Also, there are a dozen vacuum connection points, starting with a few under the good. There are check valves, junctions and the yellow plastic hoses that interconnect everything.

Spend a lazy afternoon walking through the system and hunt for vacuum leaks.

-CTH

[silverbenz]

Until then, my rear and passenger doors are stuck in the unlocked position. Can I disconnect the vac lines and operate (lock) them manually
until I find the system problem, and if so where is a good place to disconnect these 3 doors? My maual has no vac diagram.
As of now, I can't lock my car, and occasionally travel the ghettos
of California!

thank you,
Baron

[cth350]

It's been a while, but manually locking the doors from inside the car should always be an option.

-CTH

[silverbenz]

That's what what I would have thought, but when the automatic vacuum system went out, the drivers lock works fine w/key, even smoother than before; but the other three lock buttons are stuck 'up' , unlocked, and if I try to push them down, they do not budge. It's not even like they are 'compressing air' in the tubes, they are rock solid stuck up.
Just not sure where to begin the beguine on this one.

thank you,
Baron

[johnathan1]

Start by testing each diaphragm to see which one is leaking...

I believe the locks should work manually if vacuum is present (while the car is running)...so let the car idle, then try locking them manually again.

[silverbenz]

I tried your suggestion; but engine running or not, the lock buttons
are up and hard as rock. I applied about 5 lbs of pressure, didn't want to push any harder. Again, the drivers door works w key only, other 3 are stuck.
Which diaphrams are you refereing to and where are they? I'm sorry,
I have no door/vacuum diagrams/chapters in my shop manuals for this car.

thanks, you guys are great,

Baron

[Blue 72 250]

My manual locks get very stiff if I dont use them a lot. Then the linkage will not want to budge. I would assume that you are seeing a similar result. You are going to need to remove the panel off of the door and lube em up.

[mb-novice]

I'm completely new to this, ive very recently ( 2 weeks ago ) bought a 72 300sel with the same problem, and what works for me, is locking the driver's door from outside when i get out, and then opening every other door and manually locking them. it seems to only work that way

[silverbenz]

mb-novice, my prob must be different, as I cannot push the lock buttons
down at all, in any situation, except the drivers door, which functions with the key. the passenger door has a keyhole, but the key will not lower
the lock, hard as a rock.
I don't think it's a lube issue, as it happened suddenly; one day the system just stopped working. It wasn't a gradual thing. I'm wondering,
are the locks connected in series, starting with the drivers door? It makes sense, that maybe the problem is between the drivers door and the other three doors.
At this point I'd be satisfied if I could just disconnect the vac lines to the other 3 doors, and keep them locked manually, and open/close my drivers door with key only. There's a line to the trunk too.

In spite of all this vacuum crap, damn, I love driving that car around.
That air suspension is AMAZING.

-Baron von Krieg

[cth350]

Time to remove the driver's door panel. -CTH

[wbain5280]

Yes, remove the door panels and you'll see the linkage. It may be a simple fix, like oiling them.

[Tomguy]

You can clean and oil the mechanisms for manual operation. You can take the rubber diaphragms off and clean them with denatured alcohol, and put a layer of silicone over them for the vac locks to work again. Replacements are available for around $5/each I believe. Typically the trunk is the first one to go. Make sure your check valve in the engine bay is working.

This can help:
http://www.peachparts.com/shopforum/attachments/vintage-mercedes-forum/14000d1070976056-72-280-se-looked-today-info-needed-locklines2.jpg

[silverbenz]

I pulled off the drivers door panel, and the small vacuum spool valve that screws to the door body, had come loose; the vibrations had backed out both screws and it was 'floating free' held in place by only the linkage and the three vacuum lines connected to it (This is part # 28 on the diagram
that TOMGUY posted). So the valve actuating rod couldn't move, as the valve body was floating free.
I used better screws, with some thread lock and remounted it. Note that the valve body has slotted mount holes to allow for fore/aft adjustment,
but I mounted it in the center, and all locks work great, even the trunk locks too.
I took the opportunity to lube all pivot/slide points while I had the panel off. It was shockingly CLEAN in there, as the previous owner had the entire vacuum system rebuilt (He threw money at this car by the thousands of $$$)
Thanks to all who helped me out here.
Baron von Krieg