Automatic Locks - PeachParts Mercedes-Benz Forum

Rothrock · #1 08-26-2007, 08:29 PM

I just got a 1972 280SE 4.5 overall in good condition. I'm pretty car illiterate, but will probably have to learn quite a bit.

I'm having some problems with the automatic door locking. It works when I lock the driver's side door – all the others go down, the trunk, and the gas cover also lock. But then the next morning they don't all go back up and the trunk remains locked.

If I start the car after a bit all the other doors do go up. And if it hasn't been very long since I parked it they work just fine.

Overall not a big problem, but I don't have the trunk key, so if it is locked I can't get in. So two questions:

Any advice on the vacuum locking system?

Is it easy to get a trunk key if I have the ignition key?

Wodnek · #2 08-26-2007, 08:40 PM

There is a vacuum leak somewhere in the system. The most likely is one of the diaphragms. Do a search on this site. I think there are a couple good troubleshooting guides in the diesel forum.

300SDog · #3 08-28-2007, 12:25 AM

Dealership can get master key for you, just show them title/registration and its surprisingly inexpensive like $15. I dont think anybody takes vacuum automatic locks seriously, rare to find them 100% operative. I'd say you're doin pretty good if they lock the car. Its common practice to rev the engine to unlock the doors.

Tomguy · #4 08-28-2007, 12:47 AM

I'd suggest checking your trunk lock diaphragm as it's the most likely culprit. Of course, it could be one of the 3 doors or the connecting lines, but the trunk one is the most likely one I'd say.

JimFreeh · #5 08-28-2007, 06:04 AM

All your locks should use a single key.

Trunk lock has several positions, you can unlock it and it remains unlocked, or you can lock it and it requires the key each time you open it.

Access the trunk vacuum lock below the trunk latch, you should see an access panel.

Disable it by blocking off the vacuum with a golf tee and see if things change.

Vacuum systems can leak in a lot of places, get a mighty vac and test the system.

Jim

jaimekop · #6 08-28-2007, 08:39 AM

Don't take the "old car" excuse for poorly functioning vacuum locks... With proper trouble shooting and repairs, they can maintain vacuum for more than a week... I believe the older style (like on your 108) lock actuators have replaceable diaphrams which are not too expensive. For long term reliability, replace all of them. Get a hand vacuum pump with a gauge and use it for trouble shooting... A diagram of where the lines are run should be available in most repair manuals. Also be ready to replace any rubber connections along the way... there are also available and not expensive.

Jaime
'95 E320 - pump driven locks - it cheats
'84 300TD - Locks hold vacuum at least 1.5 weeks
'80 280SE - surprisingly, holding vacuum since I bought it, I haven't run it since!

aublutiger · #7 08-28-2007, 01:25 PM

The exact same problem!!!! I just fixed it and everything works fine. You may have more than one issue...so here's what worked with mine and maybe it will work for you....

First, you have a vacuum leak somewhere in the system. The vacuum tank should store the vacuum for several weeks with no problem...but in your case there is a leak somewhere that is allowing that vacuum to escape. It was a slow leak..just like yours...mine would work when I had the engine running for a few...or just after I had shut off. So..the key is finding where that leak is and replacing whatever part. One of the first things that my mechanic had me do was to seal off the line coming in from the vacuum tank to the door valve on the driver side. This determined if there was a leak between the tank to the door. After a couple of days of not being used, i checked and there was no vacuum. My mechanic fed a new line in from the tank to the door...as he did, we found that the old line had a split in it...so that end was solved....we checked it again and vacuum was maintained....hooked it back into the system.

Then...ended up needing to replace all three diaphrams (passenger, fuel, and trunk)...all of which I pulled from a local junk yard....so far its been running just fine!!!!

The simplest might be to check that vacuum from the tank to the door first..make sure that is okay...but i have to agree with previous posts...sounds like you need to at least replace the trunk diaphram.....

ADP · #8 08-29-2007, 12:02 PM

In both 72' 280 SEL 4.5s I've had - the main culprit was the fuel door diaphram that holds the plate closed.

I never bothered in Henrietta, but in Brunhilda my mechanic took that diaphram out of the circuit. Now my doors hold pressure for a few days, so I've got a slow leak somewhere else, likely in the doors!

Ann

300SDog · #9 08-29-2007, 03:27 PM

Quote:

Originally Posted by jaimekop

Don't take the "old car" excuse for poorly functioning vacuum locks...

Yeah but dont get me wrong, I think central locking has coolness factor all its own even if less than 40% operative. Revving the engine to unlock doors also works for priming the system to lock em if you jump outa the car and turn the key in less than 20 seconds. For family of 4 this turns every event of parking and locking the car into chinese fire drill, great fun for everybody. Daughters had hilarious fun laughing about the fact it took high rpm's from Mercedes engine to lock and unlock the doors. This feature alone makes semi-operative vacuum locks not entirely worth fixing.

ADP · #10 08-30-2007, 05:50 PM

Quote:

Originally Posted by 240Dog

...Daughters had hilarious fun laughing about the fact it took high rpm's from Mercedes engine to lock and unlock the doors. This feature alone makes semi-operative vacuum locks not entirely worth fixing.

Mmmm, this was another reason why my non motorhead spousal unit raises a skeptical eyebrow when I suggest an actual roadtrip in the car.

Not once, but twice, he has had to stand at the passenger door while we've had a torrential Southern cloudburst and I unlock the driver's door and start the car...

"No, you aren't climbing over my brand new sheepskin seat covers with your dirty feet - your umbrella works just fine. Stand there and wait!"

Ann
who had an uninterrupted stretch of 95 mph+ today : )

cth350 · #11 08-30-2007, 07:27 PM

Ann, get a pair of the tevic suits used by painters to keep their cloths clean and the cute booties too. Put a set on and show him the other set and say "time to go for a drive". That should scare him straight.

The other cure for getting wet is to open his door first with the key.

-CTH