How do vacuum locks work?

[Baxterdown]

Hi guys,

I replaced a driver's door-lock broken clip on my 1972 W108 and my car's vacuum locks are now working! But, I'm not sure if they're operating correctly. So, I have a few questions:

OPENING LOCKED CAR
When I turn the key on the driver's door and unlock the car, should all locks unlock? Mine don't.

STARTING CAR
As a follow-up to the question above. When I unlock the driver's door, the other three locks don't unlock. But, the second I start the car, they do pop-up and unlock. Is this normal?

ENGINE RUNNING
Just because I know y'all are gonna ask :-) LOL! When the engine is running and I'm in the car, all locks lock and unlock when I operate the driver's door lock.

Also, a couple of related questions...

STICKY LOCK
The rear passenger lock is sticky. It goes up no problem, but will not go down fully. If I push it down manually it does go down with little effort. I'm not sure it's a vacuum problem. I'm thinking its a lubrication issue. Any thoughts?

DRIVER'S DOOR
I have to push in with the key to lock/unlock the driver's door. Any idea on how to fix this?

Thanks!

Jose

[Tomguy]

Lock operation:
There is a vacuum tank in the LEFT FRONT fender (behind the rocker panel) that stores vacuum for when the car is not running.

The doors should ALL lock *AND* unlock when the driver's door is. This is the same with the gas door AND the trunk as well. The gas door requires a vacuum to stay locked, so if your system leaks, it will not stay locked.

The driver's door lock CANNOT be pushed down when the door is opened. Idiot-proofing, German style. You need to use the key, or open the rear passenger door and lock that way.

If your locks only work when the engine is running, and don't even work properly when it's shut off you have a MAJOR vacuum leak. That's normal. The 40 year old rubber diaphragms don't hold up. You can find replacements, or clean yours really well and coat them with a layer of silicone. The slow lock is probably a bad diaphragm. The door locks are spring-loaded so they can be locked/unlocked, with resistance, without moving the diaphragms, so this sounds like what you're feeling.

[Baxterdown]

Tomguy, thanks for the reply. To further clarify:

All my doors (with the exception of the sticky one) do work with the engine off, at least in part. After I turn off the engine the doors will lock when I lock the driver's door. It's only when I try to unlock them with the engine off that they won't unlock.

As I'm typing this I just remembered that I tested the vacuum system when I was installing the pin by pushing the vacuum pin on the driver's door in and out several times and all the doors locked and unlocked (the engine was off) perfectly. I'm starting to wonder if I did something to that one vacuum. I'm gonna check it tomorrow!

[ScooterABC]

Originally Posted by Baxterdown

Tomguy, thanks for the reply. To further clarify:

All my doors (with the exception of the sticky one) do work with the engine off, at least in part. After I turn off the engine the doors will lock when I lock the driver's door. It's only when I try to unlock them with the engine off that they won't unlock.

As I'm typing this I just remembered that I tested the vacuum system when I was installing the pin by pushing the vacuum pin on the driver's door in and out several times and all the doors locked and unlocked (the engine was off) perfectly. I'm starting to wonder if I did something to that one vacuum. I'm gonna check it tomorrow!

So you have leak(s). When the engine is running you have sufficient vacuum to exceed the leaks. Leaks can be in the actuators or in the lines/junctions for the lines. Leaks can be in either the "lock" circuit or the "unlock" circuit or both. You need a Mitivac to diagnose the problem. Do _not_ just start replacing things.

I don't know how things are routed on a 108, but on a 123 most of the good stuff is under the carpet on the front passenger side. You take up the carpet and identify the junctions. On a 123 the "lock" circuit is color-coded differently than the "unlock" circuit so what you can do is find a junction and apply vacuum and see if something locks or unlocks. Then see if while applying vacuum the vacuum pressure is holding. If it isn't, then you have a leak down-stream from there. As an example, on a 123 I _think_ that the unlock and lock lines found under the right front passenger carpet control the front and rear right doors, the gas cap, and the trunk. So if you try to either lock or unlock from that position and you aren't holding vacuum you need to move one step further down the line to see which one(s) are leaking. So you move down-stream to the line that just operates the rear door. See if it holds vacuum for lock and unlock. If it does, it's fine. etc.

The fact that it locks everything right after you turn the engine off means very little. See what happens if you turn the engine off and DON'T lock the doors, and come back in an hour and see if you can lock the doors then. If you can't then you have a leak in both the locked and unlocked circuits.

I think there is a tutorial on one of the websites, possibly diesel giant, but I don't know for sure.

[Baxterdown]

AHA!

This morning I remembered that I had disconnected the line into the gas door lock when I first got the car because it was malfunctioning and it had locked on me at the gas station once. I didn't want to take any more chances until I fixed the clip.

I reconnected the line and all is good now!

I've driven the car around this morning and the doors are working just like you guys described and open and close (all four, including the one that was sticky) when I lock/unlock the driver's door with the engine off and on. Fingers crossed!

The only thing left now is figuring out why do I have to push driver's door knob/key in to engage the lock (for locking and unlocking). Any thought?

Jose

[ScooterABC]

Originally Posted by Baxterdown

The only thing left now is figuring out why do I have to push driver's door knob/key in to engage the lock (for locking and unlocking). Any thought?

Please clarify - are you saying that you can't turn the key in the lock cylinder unless the key is button is pressed in, or are you saying that you CAN turn the key but it does nothing unless the button is pressed in?

If you can turn the key without pressing in the button then you probably need to adjust the length of something (but I'm not sure what). If you can't turn the key without pressing in the button then I think you have a worn or incorrect key or that the spring return on the button isn't applying any pressure. What happens if you hold the button out with one hand and try to the turn the key with the other?

[Baxterdown]

ScooterABC, the best way to clarify is with a video demo!

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

[ScooterABC]

OK so the lock cylinder is fine but the lock actuator isn't hitting where it is supposed to hit to lock/unlock. Take off door panel and see what is happening inside door would be my next suggestion. It shouldn't be working like that.

[Adv_rider]

Guys, where can I find a vacumm diagram for the W108? .. 1972 280SE 4.5