vacuum lock problem on 1987 560SL
 

Hello All,

I have this strange problem with the passenger door lock on a 1987 560SL.

I can unlock it from the driver side door central control just fine, however when I go to lock up all the doors from the driver door lock using the central locking system, it fails to lock the passenger door lock!

I thought it was a vacuum leak but then I would not be able to unlock using the central locking system would I?

I have to go, manually lock the passenger door lock with my key and then it locks.

One thing I did notice, once I've activated the central locking system, I can go to the passenger door, open it, lock it using the key, close the door...I then hear two or three popping noises and the door then locks!

any ideas?

dom

more symptoms
 

ok, here's more stuff to hopefully help someone diagnose the problem:

If I use the master key and lock the passenger door, it also locks the driver's door...it also unlocks both doors when I do it from the passenger door lock....

I can still unlock both doors from the driver door lock but not lock the passenger door.

So which door lock is malfunctioning?

My guess is that neither lock is malfunctioning... rather the problem is probably in one of the wires that plug into the passenger door lock mechanism. Again my guess is that the problem is caused by corrosion either at the plug or somewhere along the inactive wire.

Has the floor of your car ever been flooded... especially back seat passenger side?

If I recall correctly there is a wiring harness under the rug just about where the right back seat passenger would put their feet. The wires are brown or brown with black stripe. A number of them run together at that point and are crimpted together. They tend to corode with a green powder... especially if the rear window has been left open during rain storms.

Check the plug at the front door lock first and then if necessary do the rug thing. To access the junction of the harness... remove the right rear passenger side door sill, rear seat cushion and whatever else necessary to lift the rug. lift the pad under the rug and cut open the harness with the brown wires in it. Find the junction and repair as needed. I soldered mine.

;)

thanks for the info!

please confirm that I'll have to remove the door lining on the driver's door to get to this "plug" you're refering to?

being an SL, there's no back passenger seat but will check the area under the rug directly behind the passenger seat which would correspond to your instructions and look for corroded wires.

don't know if the floor has ever been flooded, have owned the car less than three weeks and bought it from a wholesaler who had no clue as to its history or value.

thanks again for the info

dom chang

I would check the passenger side actuator and door latch. There is a small adjustible connecting rod between them. My guess is that something is loose or the actuator end broke off (this would explain why you are bale to unlock, but not lock).

Vin

dom,

Never locked my doors before closing them, but I did have some strange symptoms something like yours. For example, I could not lock the Driver door from the passenger side. Maybe the popping noise is a lube or alignment problem in the passenger door locking system?

I have not truly mastered the Germanic intricacies of the locking system, but seems to flow naturally from using the passenger door only with a lady passenger, locking and unlocking doors for her with the master key, and keeping valets out of the trunk and glove box by passing them the other key.

I found a surprising solution to my particular symptoms.

I bought a new master key from the dealer for my VIN# just to have a spare. The New master worked all locks just as the manual indicates locks should work. Not so with the old, worn master. The master and secondary key do not work all the locks the same way.

I have no idea if you problem is a worn master key, but if all else fails....

I would suspect the its the passenger door plug that has the problem but then again it might be that the driver's door is not sending the signal.

Because your car is different from mine I would trace the wires from the vacume motor. Mine is under rear seat.... don't know about your model.

thanks to all for your feedback, have narrowed it down to the locking mechanism on the passenger side door....I cannot detect any vacuum leaks or hissing noises as I work the door locks so I believe that the lines are ok.

not sure on taking the door lining off to get a closer look at the connector rod mentioned by vinamg, with my luck, I'd end up breaking something and not be able to put the door lining back on!

Maybe I will have the auto shop look at it next time I take it in, it's a minor nuisance right now, couple that with the beginning to come loose door handle on the driver's side, and it could become something major but for now I can live with it.

thanks for your help

dom

ok, decided after researching "door lining" on this website and finding great instructions that I could handle the removal of the door lining.

did so, checked out the vacuum line leading to the lock actuator, it was fine...unhooked it from the actuator and could feel air moving when unlocking/locking the locks.

removed the lock actuator and hooked it up to a different vacuum hose which normally activates the gas cap door lock, it worked fine as well.

the lock mechanism rods and connectors looked fine though they moved stiffly so I applied liberal amounts of WD40 till they got smoother...hooked everything back up and voila, now all door locks unlock and lock no matter which doorlock I use the keys on!

I do have to hold the key in the lock position about five seconds to give the vacuum at the passenger door lock a chance to apparently build up and activate the lock but it beats having to walk over to the passenger side to lock the door manually!

there's still a buzzing sound coming from the vacuum pump in the trunk after I've unlocked the doors like it's trying to build up the vacuum reserver but it's something I'll guess I'll get used to.

thanks again to all who provided advice and feedback, it helped greatly not only to narrow down the problem but encouraged me to get this done.

dom

Now before you button the door skin up Dom, you might want to clean the lock linkage and lightly lube it with something longer lasting the WD-40. Maybe some white lithium or similar grease.

doh! too late, she's all buttoned up.....will put the lithium grease on those parts next time I've got the door lining off.....or is there a prescribed grease?