W126 door lock puzzle - PeachParts Mercedes-Benz Forum

gregga · #1 10-10-2006, 04:43 PM

My '89 420 SEL door locks have been keeping me up at night. If I lock the car from the trunk, the alarm will sometimes go off a couple hours later. If I open the driver's door from the inside while the engine is running or after the aux vac pump quits, all the locks open. If I pull the door handle after the engine is off but before the aux quits, only the driver's door will unlock. The lock knob cannot be used to unlock at this time as vacuum is pulling it down. When the driver's door is the only one unlocked, the key won't lock it from the outside unless it is turned HARD to the open direction until the lock pops, then it will work. If the passenger lock is opened and locked, inside or outside, it always opens and locks all the locks, even if the driver's side is stuck. As soon as the aux pump quits, the driver's lock works from the outside normally. I replaced the door handle thinking it was in the electric switch but no change. Also replaced were the vacuum operators in the driver's door. No change. Any thoughts?

whunter · #2 10-10-2006, 05:44 PM

Sounds like Four issues are possible.
* Vacuum leak.
* Mechanical binding in latch and/or linkage.
* Electrical short.
* Alarm malfunction.

Factory Alarm System Issues
http://www.peachparts.com/shopforum/showthread.php?p=1143583

Door LOCK issues, link thread.
http://www.peachparts.com/shopforum/showthread.php?p=1214456

Have a great day.

gregga · #3 10-10-2006, 08:56 PM

Well, the passenger door works fine when the driver's door doesn't. Would the leak be in the driver's door? And why does it work fine after the aux pump quits but not before? The aux pump HAS to shut off or the engine has to be running to have the driver's door open all the other doors. The passenger door works no matter what. And there isn't binding, the lock knob is held by vacuum force. If you are strong enough, you can pull the knob up. It works freely after the aux pump quits or the engine is running. And the only time the alarm goes off is when locking the car through use of the trunk lock. And then it waits a couple hours to go off. Why not other times? The links don't address anything like this.

Hatterasguy · #4 10-10-2006, 09:44 PM

Disconnect the alarm, problem solved!

Sounds like you have a leak, vacuum leaks can be a royal pita to track down. Get out the vac diagram, a beer, a vacuum tester and go at it.

The W126 has a seperate vacuum system for the door locks. They shouldn't care if the engine is running or not, thats what the pump in the trunk is for.

whunter · #5 10-11-2006, 01:29 AM

Quote:

Originally Posted by Hatterasguy

The W126 has a separate vacuum system for the door locks. They shouldn't care if the engine is running or not, thats what the pump in the trunk is for.

Unless some previous owner/technician butchered the vacuum/lock system together.

Hatterasguy · #6 10-11-2006, 07:16 PM

Yeah that would never happen!

Is so God help you, hope you can figure it out!

whunter · #7 10-12-2006, 01:12 AM

Quote:

Originally Posted by Hatterasguy

Yeah that would never happen!

Is so God help you, hope you can figure it out!

It will allow him plenty of time to catch up on consumption of his favorite adult beverage, (and four letter word practice).

blueeagle289 · #8 10-12-2006, 06:43 AM

The alarm system on this particular car seems to be very sensitive. I had a problem with mine going off when parked in a heavy wind area (and we get quite a bit of that in Dallas at times). I finally just disconnected the alarm system -- under the passenger floor board area on the right side; two connectors. I have had no more problems. If your alarm is in fact the base problem, I would just make it inactive.

gregga · #9 10-12-2006, 08:35 PM

The language and drinking levels might surprise you. In the pictures are a few of the tasks I've already undertaken. I don't like disconnecting an alarm system tht works fine as long as I don't arm it from the trunk lock. The door locks all work fine as long as I unlock before shutting off the engine or waiting until the aux pump quits or lean over and open the passenger door. This all tells me things that will lead me to the correct solution, getting it to work the way it was designed. I just haven't figured out the clues yet.

demuniga · #10 09-09-2012, 04:01 PM

In the process of getting rid of my wife's 1987 420 SEL. After 20 years in the family and 199,000 miles it is time to have it go to a good home. Someone is going to get a great car!

I had the same problem as gregga where the drivers door only locked/unlocked with the key & the passenger's lock mechanism would unlock the other doors + the fuel door & trunk.

Instead of pulling apart each door panel to see where the leak may be in the actuator or line, I pulled up the driver's and passenger's carpet to get access to the yellow vacuum lines. One by one I used a golf tee to isolate the actuators in each door & attempt to operate the lock system. Sure enough, when I plugged up the right front door vacuum line the other three door locks worked flawlessly with my keyless remote.

Keep up the great work on this forum. This site has saved me hundreds of dollars with the tech advice from other members.