Door Lock Issue - Front door will not lock

[billsutton]

My right front door does not lock. Insert the key in right or left door lock, and the lock knobs raise and lower. All the other doors, trunk, fuel cap, lock, but not the right front.

The car was recently repainted, all the panels removed. The paint shop looked at it, removed the interior panels, lubricated the actuator, and said the problem is a faulty actuator. It may be, but before I chase down that hole, has anyone experienced a similar problem and encountered a faulty actuator?

 

[gsxr]

Bill, just to clarify... the right front door lock knob does not raise or lower UNLESS you have the key in the right front door, correct? And if you lock / unlock from the other door or trunk, the right front does not move?

If so - it does sound like possibly a faulty actuator, but you'd also need to check the vacuum lines. The central lock system is vacuum actuated with electrical signals.

BTW, welcome to the forum!

 

[8899]

Bill - welcome to the forum!



Please start an OWNER thread, add some words about your car, where/when you got it, what you have done to it ....and of course a photo of that freshly re-painted beauty!

 

[billsutton]

Problem at last resolved. It was not the acuator, but rather a mechanical connector that had bent over time. Not an easy fix, involved complete dissassembly of door panels

 

[zentoed]

I had this same problem and was happy when a searched turned up this thread. It turns out my latch mechanism was indeed bent as well. So if figured I would add some pictures of what I found in the hopes of helping someone else.

To be clear, the symptoms here are that the lock knob goes up and down manually or as a result of activating the central locking system BUT the door will open whether the knob is up or down. Another thing you may notice is that the door lock knob has very little movement.

 

[gsxr]

I had this same problem and was happy when a searched turned up this thread. It turns out my latch mechanism was indeed bent as well. So if figured I would add some pictures of what I found in the hopes of helping someone else.

To be clear, the symptoms here are that the lock knob goes up and down manually or as a result of activating the central locking system BUT the door will open whether the knob is up or down. Another thing you may notice is that the door lock knob has very little movement.

zentoed, THANK YOU for posting the additional description & photos. A car I bought a few years ago has the issue you describe, but I haven't had time to investigate yet. Sounds like it may be exactly what is shown in your photos. I'll add to this thread when I get the door taken apart...

 

[zentoed]

I have been giving some thought as to why/how this problem develops. My theory is that failure of lubrication of the door latch mechanism is probably to blame. What I observed when I had the latch in my hands and was trying to understand its operation, is that the the door latches in two steps. When closing the door, the latch encounters the striker on the door jamb and rotates through two detents. It is only once the latch engages the second of the two catches that the door lock knob can be depressed and the door locked. If you try to depress the lock knob with the door latch not completely engaged, it physically cannot move the components inside the latch, even though the door lock knob may move a little bit. The engagement of the second detent clears the way for the movement of the internal locking components.

So, in my case the door latch had some resistance to rotating to and through that second detent, but the door for all intents and purposes was closed securely. It appeared to be closed completely and tightly. But I suspect it was only on the first detent. In this state, if you apply enough force by hand, you will likely bend the latch components over time. This car had some inconsistent driver door power lock actuation from the day we got it, but I suspect loaning it to a family member while their cart was in the shop, may have brought the problem to point of more noticeable failure.

The other thing I noticed is that the power locking mechanism has a lot of slack, or slop, or vagueness in its action. Even with my latch bent as it was when I disassembled it, operating the power locking system resulted in the door lock knob in question moving downward some amount and have it appear that the door is locked. I don't think that the vacuum actuator is capable of putting enough force on the system to bend anything.
I think at some point I will have a look at the other doors to prevent a similar failure and investigate further.

So, it may be a good idea to periodically check your doors to ensure they do not, in fact, open even when the door lock knobs are in the "locked" position.

I saw another post about the importance of door latch maintenance and lubrication and you can add this type of failure as another reason to keep up with that.

So, that is my theory.
Your mileage may vary.

Tony

 

[gsxr]

In today's episode of "Don't Do What Donny Don't Does":

I encountered the problem described above after loaning our beater E420 to a family member. I now believe the root cause of this issue is the lock knob being forced down with the door open. If someone doesn't realize Mercedes driver doors must be locked with the key from the outside, they may keep pushing down the lock knob! If the lock knob is forced down, it will bend the lock mechanism as seen in @zentoed's photos. Most domestic vehicles allow pushing the knob down and closing the door, which can result in locking keys in the car. Now we know, if loaning a car to a non-German-car-driver, make sure to educate them on the German lock procedure!

Since this was a high-mile, not-exactly-pristine 034, I was reluctant to spend several hours extracting the lock mechanism from inside the bowels of the door cavity. And then trying to re-install it. FSM job 72-250 doesn't look fun. And, it looked like the parts which "needed unbent" (sic) might be accessible with some creative metalwork. At first I tried drilling holes for access, but this didn't provide quite enough space, and then I discovered the upper slotted tab was bent as well (this connects to the outer door handle). So, I took a Dremel with small cutoff wheel and created an access flap.

With the flap open, there was enough room to bend the mechanism mostly back into shape. It wasn't great, but it got the mechanism working again. At least until I installed the door panel and drove the car around the garage to park it... and it wouldn't lock! Gaaaa! Now what? Took it apart, inspected everything, fiddled some more, tested fine... re-assembled, same problem. Great.

Third time apart, I discovered the problem now only occurred with the door panel in place. Turns out, the lock rod was slightly bent as well! This caused the plastic knob to jam against the door frame and prevent fully locking, even though the mechanism below was fixed. After straightening out the lock rod, everything worked normally with the door panel installed.

Obviously this surgical procedure s isn't recommended for any nice 124, or any 036... but for a beater, it will get the driver door locking again. I still have another car that needs the lock assembly removed and bent back into place, haven't had time to mess with that project yet.

Photos below of the butchery.

The faint of heart may want to avert their eyes.

You've been warned.

 

[Jlaa]

In today's episode of "Don't Do What Donny Don't Does":

I encountered the problem described above after loaning our beater E420 to a family member. I now believe the root cause of this issue is the lock knob being forced down with the door open. If someone doesn't realize Mercedes driver doors must be locked with the key from the outside, they may keep pushing down the lock knob! If the lock knob is forced down, it will bend the lock mechanism as seen in @zentoed's photos. Most domestic vehicles allow pushing the knob down and closing the door, which can result in locking keys in the car. Now we know, if loaning a car to a non-German-car-driver, make sure to educate them on the German lock procedure!

Since this was a high-mile, not-exactly-pristine 034, I was reluctant to spend several hours extracting the lock mechanism from inside the bowels of the door cavity. And then trying to re-install it. FSM job 72-250 doesn't look fun. And, it looked like the parts which "needed unbent" (sic) might be accessible with some creative metalwork. At first I tried drilling holes for access, but this didn't provide quite enough space, and then I discovered the upper slotted tab was bent as well (this connects to the outer door handle). So, I took a Dremel with small cutoff wheel and created an access flap.

With the flap open, there was enough room to bend the mechanism mostly back into shape. It wasn't great, but it got the mechanism working again. At least until I installed the door panel and drove the car around the garage to park it... and it wouldn't lock! Gaaaa! Now what? Took it apart, inspected everything, fiddled some more, tested fine... re-assembled, same problem. Great.

Third time apart, I discovered the problem now only occurred with the door panel in place. Turns out, the lock rod was slightly bent as well! This caused the plastic knob to jam against the door frame and prevent fully locking, even though the mechanism below was fixed. After straightening out the lock rod, everything worked normally with the door panel installed.

Obviously this surgical procedure s isn't recommended for any nice 124, or any 036... but for a beater, it will get the driver door locking again. I still have another car that needs the lock assembly removed and bent back into place, haven't had time to mess with that project yet.

Photos below of the butchery.

The faint of heart may want to avert their eyes.

You've been warned.

@gsxr, the upper butchery is clean with nice incisions, but the bottom butchery is ..... medieval! I think, after you bask in the smug satisfaction of a job well done, you will want to clean up the drill-holes with cleaner incisions!