1980 300SD frozen door locks - not temp related....

[dunl]

My locks are frozen in the unlocked position, and I'm hvaing trouble finding out why.  Here's what I posted on www.mercedesshop.com.....

1980 300SD

Bought this with non-functioning door locks. After working on the shut-off vavle leak, I have decided to jump on this one. First some info:

1) Door locks do nothing at all, except for the pull handle/knob locking thingies (feel free to name these for me) are in the upright position, and remain so all the time. The drivers one is completely disconnected, and can be lifted out of the hole.

2) Pushing down to lock the doors is prevented by heavy resistance. I say resistance, as it SEEMS to move a slight bit downward, but I'm afraid to go harder and break something.

3) Yellow line and yellow line with brown stripe going into the cabin through the firewall. Yellow line appears to have excellent seal - its counterpart with the brown stripe appears to have heavy leakage. I haven't been able to source a MityVac locally in my area, so I simply sucked on the line. While I can feel suction on other lines I have tried, and tell if there are good seals, this line feels like it is completely disconnected somewhere, and I am simply pulling as much air through the line as can be pulled - without resistance of any kind.

4) Key does nothing to the locks. Works to manually open and close the trunk.

I'm wondering if the levers for the locks on the doors remaining in the upright position are a symptom of anything particular, rather than just a symptopm of something being wrong.

Also, what is the best way to track down this problem? I can simply start ripping apart the doors on the vehicle, but if there is a more intelligent way to go about it, that would help a lot.

Thanks,
Dunl

Any 116'ers on here that can help a newbie out?  Thanks.

[michaeld]

Dunl,
I'm no expert on the door locks, but I'll pass along what I do know.
First of all, the doors operate by vacuum (it sounds like you knew that, but just making sure!), which is the source of resistance when you push down.
The other thing is that the only mechanical lock on the system is the driver side door.  It is the only one that responds (easily, anyway) from the outside w/ the key.  It is the driver's side door that "arms" the system.  Obviously, if you can lift the whole assembly out of the hole, there's a somethin' very wrong with it!  I would suggest that you repair/replace that unit first and foremost, as the other doors simply won't function correctly without the "master" driver's side door being in order.
Hopefully, someone w/ more experience than I will have something more detailed about the door locking system.  Good luck with it.

Mike

[dunl]

Okay, that helps. I knew about the vacuum, but I didn't know that the driver's door operated the whole system, as I thought with the passenger side lock as well, the front doors operated the rest (or impeded as the case may be). 

The whole assembly doesn't lift out, just the lever on top of the inside door cover used to manually lock and unlock the doors.  Looks like either the thread broke off (now that it's disassembled), or someone replaced the shaft under it.

Thanks, that's helps some. 

[oscar]

Just another note, it sounds like the driver's side door knob may be threaded.  Regardless, the thread of that shaft should poke through the door lining near the window when the door is unlocked.  You should be able to pull and push that thread/shaft to operate the lock.  CAUTION That particular lock will only operate when the door is closed.  That lock can't be physically operated whilst the driver's door is open.  It's mechanically impossible. 

As far as the passenger doors are concerned, feel free to push or pull the knobs despite the resistance.  Even without a vaccum present, or doors open or closed, the rubber diaphragms in the vaccum elements that operate the locks will provide resistance and you wont do any damage.

Back to the driver's door, it also sounded like that vertical shaft that holds the knob is disconnected, Am I right?   I'm not sure.  Eitherway check the linkages between that vertical shaft and locking mech then the horizontal shaft from there to the master switch (round black barrel with the three vaccum lines attached), you'll also be able to check the 3 vaccum lines on the master switch.  Again the door has to be closed to operate the lock.  Obviously too, the inner door lining has to be removed to view and manipulate the linkages.

So check these physical parts first before you worry about the rest of the vaccum, .  That is of course if it's a mechanical problem as I'm assuming from what you describe.  I'm also assuming you know how to take the lining off.  One piece of advice after you've remove small parts, handles and trim from inside the door, bump the moulding upwards to remove.  Let us know if you need more info.

[oscar]

Sorry Dunl, forgot something. 
There is a way you can test the lock of the driver's door with the door open.  Simply put a pen, or your finger or screwdriver sideways into the area of the door's latch that would hit the strikeplate on the pillar.  Once that part clicks over, it's as if the door's closed and you'll be able to operate the lock mechanism.  Just remeber to pull either the inside or outside door handle to release the latch and simulate the door opening, before you shut the door again.  There's a  possibility that with a good push the latch will be damaged when contacting the strikeplate if it's already set in the closed position before you try closing the door.

[oscar]

Hey Dunl, can you believe I left something out.

In my car the yellow line with stripe goes to that master switch I mentioned earlier.  Thicker yellow line no stripe goes to vaccum tank in the boot/trunk.  Some models may be reversed with the stripe going to the tank. 
With the door lining off you'll see if it's disconnected at the master switch. 

The vaccum tank is located under the parcel tray but accessible thru the trunk sitting above the fuel tank.  With a torch and your head looking towards the left hand side, you'll see a yellow line of some kind going thru a rubber grommet connecting it to the tank, unless it's fallen out of course.  This line out of the tank is as just a likely cause of central locking not working.  Good Luck.

[John Hubertz]

Is that the standard w116 location for the "egg crate" vacuum canister?  I know my 107 had it in the front fender....

[OzBenzHead]

Is that the standard w116 location for the "egg crate" vacuum canister?  I know my 107 had it in the front fender....

I believe so, John. It's where mine is, and also those of my W116 friends. My W108 has it in a nacelle in the front LH fender - in a similar place to where the NA 116 has its climate control vacuum tank.

[dunl]

Thanks for the tips guys, I'll respond to each.

mb350: yes, the vertical shaft that holds the knob is disconnected, and there is no thread that is apparent on it. (should be an easy fix, with a new shaft and a die of the correct size, I would think, or possible a threaded one if I can find one).  I'm sure I've tried it with the door closed, but I will try it again to make sure.  I did get the correct procedure for removing the door, and thank God, cause I'm sure I'd be asking for replacement clips right about now.    I think I'll stick to testing it with the door closed, as I don't want to make more work by messing with the latch.    As for the trunk tank...are you sure my model comes with one?  I haven't checked yet, but I was told in the past that it was only on later models, not mine?  I'll check it though....


John Hubertz/OzBenzHead: What is this egg crate type cannister you speak of, and how is it connected? 

Thanks again,
Dunl

[oscar]

As for the trunk tank...are you sure my model comes with one?  I haven't checked yet, but I was told in the past that it was only on later models, not mine?  I'll check it though....

What is this egg crate type cannister you speak of, and how is it connected?

To answer both, I've read that W123 and W126 diesels do have a vacuum resevoir/supply tank and I'm only assuming all W116 diesels would too.

The "egg crate" refers to the shape of the flat plastic vacuum reservoir/cannister with it's multiple cup shapped exterior for strenght. See the pic below.


This is a view of my boot with the barrier (bottom of photo tilting towrds camera) removed.  Fuel tank is obvious and the vacuum supply tank is that bumpy part with yellow vacuum line entering. (Note that the line and vacuum tank connection is accessible without removing the barrier).

Whilst trying to find a schematic of a 116 300sd's vacuum system (to no avail), I came across a few posts in other forums which suggests problems to do with vacuum linkages and vacuum pumps causing problems.  If it's not the supply tank line or a loose yellow line with stripe connecting to the masterswitch in the driver's door, I'm out of suggestions.  See how you go,  here's to hoping it's still something simple.

[dunl]

Well, some success  , but not complete .

  I found the egg crate tank you were talking about, after checking all over to see if I could find the magic hidden compartment in the BOTTOM of the trunk (boot, as you call it ).  Whoops.  Anyway, nothing seems to be wrong with the line.  It appears to be secure, although it seems to enter the tank without any way to check this connection at the tank area.

   I then removed both front door panels, hoping the passenger side would give me a clue about the locking mechanism for the driver's door.  Alas, they appear to be different.  Whether one of them is an aftermarket, I'm not sure.  The driver's side allows me to actually see the locking mechanism turn, while the passengers side has some kind of a barrier that I would need to remove first.  Also, the passenger side vacuum lines appear to go into some kind of a holding tank possibly? that I can only describe as a dual-bladder or double-barrel shape.  The driver's side lines go into the black barrel as described earlier in the thread.

   I had lubricated the driver's mechanism already, and today was able to lock and unlock it using the vertical shaft.  The key, however, appears to do.....nothing.  Honestly, it doesn't even feel like it's attached to anything, and the end of the lock tumbler is notched but doesn't contact anything.  So I can now manually lock and unlock the door, but not with the key.

   The passenger side door lock is now free also, and can be locked and unlocked manually or with the key.  However, still not optimum as this would just be an inconvenience for any thief.    When locked with the key, only that lock moves, and there is a "hiss" from somewhere in the system. Aha! Maybe the culprit?

   The only other symptom was that the rear passenger lock moves the front passengers when manually engaged....unfortunately always the opposite way.   

  Guess I will keep looking, but thats for the tips.  Has helped a lot so far.   

[oscar]

Is this what you saw in the passenger door??  If so, this is the vacuum element that operates the lock.  There's one of these in each of the rear doors as well.  Filler cap lock and trunk, plus various climate control parts have smaller single elements to actuate locks, flaps, heater water and so forth. There's none of these in the driver's door.  Hence the difference between both front doors.
Driver's door has the master switch ie:

which you've found.   The 3 lines attached to the barrel are yellow maybe striped-vacuum supply, white and black-lock and unlock (not necessarily that order, can't remember).  The white and black lines split somewhere, retain their colour code and go to each of the locks that are part of central locking.

Remember, front passenger door wont operate the locks on other doors.  Only master switch driver's door will.

Re the back door locks moving the front passenger doors'.  From what you describe this is a good thing.  It indicates a relatively air tight system.   With the lock and unlock lines going into the lock element, top pic, imagine moving that mechanism down as if locking.  The blue plastic part's fixed to the door and the black and alloy parts move together up and down. 
If, for example, the two black rubber diaphragms in view are part of the "lock" circuit, there's two similar diaphragms underneath that are part of the "unlock" circuit.  Pushing the lock down causes the top diaphragms to collapse and the lower ones to expand.  The forced change in pressures in both circuits cause a paradoxical reaction in the other door locks (except driver's door which doesn't have vacuum element). 
Hang on. How about, two 10ml medical syringes, retracted half way and conected by their nozzles with tubing.  Pull back on one plunger, what would happen to the other syringe. That's what's going on. Too easy.

I'm still thinking about the "hiss".  Not sure whether it's normal or not.  I hear a hiss when my recirculting air flap is activated on my a/c dial.  I'm sure it's just in the lines.  If your system's leaking, it may be only one of the diaphragms in one of the circuits.  Although, when one goes the others aren't far behind.

I have a couple of questions;
Did the master switch move any of the other locks?  Also, how long does your system hold a vacuum?

Run your engine, keep it running and pull the yellow line out of the supply tank after about a minute.  You'll hear the air rush in.  My line pulls out relatively easily and if the grommet comes out, it's only flared on the outside.  There's no glue or compound holding it in place and it creates a seal itself when the vacuum develops.  Run the motor for a couple of minutes again and wait a few hours.  Pull the line again and judge whether as much air rushed into the supply tank.

[dunl]

Yup, that was what I saw.  You're just FULL of good info today.   

I'll check it out maybe tomorrow, but I'm heading to bed right now. It's 10:39 PM right now, and I'm too bushed to take in everything you're saying correctly.

Thanks, we'll chat again.
Dunl