450SL - Help diagnosing door lock problems: vacuum or mechanical? Pic included
 

Alright, here goes. I am trying to figure out what is going on with the drivers side door locks in my 1980 450sl. When I decided to look at this, I thought I was simply going to be looking for a broken vacuum line or whatnot in the actuator, but now after looking at it for a little bit, I’m not exactly sure what the problem may be or if it’s purely vacuum, purely mechanical, or both. I will try my best to explain what is going on, so hopefully someone can help me out. Let me start off with what I know so far:

1) The door doesn’t seem to lock or unlock with the key. I always leave it unlocked anyways, so I’ve never had it functioning properly

2) The black lock lever (number 1 in the picture) has always stuck out a little bit like this. When I try to press it in all the way, I can’t get it to go in.
a. I am thinking this is because of vacuum in the actuator (3 in the picture). When I manually pull down on the connector between the actuator and the actual door catch, I can hear it release air

3) The lever (number 2 in the picture) was screwed in very tight. Almost so I couldn’t even manually get it to rotate

So I guess there are a lot of potential issues here, and I’m trying to figure out how to narrow it down and a) get the lock working and b) get the vacuum to work properly. Part of the problem is that I am not sure what position the vacuum actuator is in (if it is a locked position or an open position), so it’s hard for me to test different situations.

Are there certain things I can test for to figure out what the state of the door is, and then go and fix it to what it should be? What if I were to disconnect everything and kind of just re-assemble it to a certain state (either locked or unlocked) so I can go from there?

Any thoughts or advice would be greatly appreciated. Thanks!

Could be lots of things on that car....sounds like you are getting pressure from the system, so doesn't sound like a vacuum problem - or you could not have enough pressure to move the actuator.

The black switch (the interior door lock) will always stay flipped out when unlocked or when the door is open (it will not lock when door open).
I would check for leaks and then lubricate the connections.

The other problem could be the vacuum reservoir - you are getting some pressure, but maybe not enough to make the door locks move. I think the vaccum reservoir on your car is under the hood (big plastic tank looking thing).

Thanks JFawcett.

I think I'm getting enough pressure from the reservoir, but just so I can make sure, how much should I be getting?

That makes sense with the black switch. I was always trying to do it with the door open. So I should close the door to try and see if that works or not.

As for the hinge part, should that be screwed very tightly to the door frame, or should it be pretty loose and rotate easily?

Alright, I tested it...
 

...and you were right. When I closed the door, i was able to lock the door with the black switch.

I got out of the car and closed to the door to test the passenger door and trunk. When I turned it once to lock it, I noticed that the passenger door did not lock, but the gas flap did lock.

Then when I went to unlock the door, I turned the key once and the gas flap stayed locked (although the driver door unlocked). I turned it a second time and the gas flap unlocked.

Is this normal? Should the gas flap unlock on the first turn of the key, or should it take 2 turns to do it? Also, the same question for the passenger door.

Thanks!

Good news on the locking....I think you have a vacuum leak.
The vacuum should have enough pressure to lock and unlock doors, trunk and gas tank 3 or 4 times. Then you need to start engine to re-pressurize system.
I would work from the driver's door to test the system - as that is the master lock on the car.

Not sure about your year, but do you have an alarm on the car? Could have been disconnected and that COULD be part of problem with locks.

I would start trying to determine if you have a vacuum leak. Look around the tank first - look for any deteriorated rubber connectors, anything around the door hinges (hidden by the rubber boots).
good luck!

vacuum issues can be difficult to find. Do you have a vacuum tester ( mityvac) they are a must . Start central , work until you find a line,pod or device not holding vaccum

Door lock tumbler....