Troublesome central locking W123 1982 280E Manual

[JohanCNel]

I would appreciate it if the members could provide some assistance in solving my troublesome central locking.

The central locking does not work when the car is turned off, but when it runs, it opens all the doors, but wil not close when I press the driver door lock. It also seems to have stuck in open for the fuel cap and also the boot.

Is there two vacuum systems? Is the vacuum system for the central locking part of the mechanical (engine) vacuum? Why does the speed control also not work? Are all these problems related?

Thanks for the help in advance

Regards,

Johan

 

[Mikesmerc]

Hi Johan
you may find that one or more of the rubber vacuum diaphrams may have perished due to age(blue plastic units inside door panels linked to lock) resulting in loss of vacuum. All the 123s I have owned through the years had similar problems. Its been a about 8 yrs since I tackled such a problem and I am a bit rusty in my explanation. Common enough problem and I am sure you will have further posts.

Regards
Mike

 

[Spike]

I found this very long but detailed article which should help you

Say 'Thank you Nathan'

Model W123 Central Locking


Diagnosis and repair of vacuum leaks in 240D door and trunk locks. Written by Nathan Carter, summer 1999. ncarter@satie.arts.usf.edu <or> mega@avatar.walrus.com

<disclaimers: I'm not a certified mechanic; however, I have owned two 240D's, which have been my primary cars for the past eight years. All the following information is more or less accurate for my 240D and may or may not be the same for other models. Also, I'm writing this from my desk and not from inside the car; it's as accurate as I can remember without looking at the car.>

I know this is long, but if you've got the door lock problem you'll want to read the whole thing, even print it out and stick it with your service manuals. The most valuable information is near the end, but go ahead and read the whole thing

Everything in the car is controlled by the vacuum system - brakes, engine shut-off, air vents, door/trunk locks, etc. There's a vacuum pump in the engine, vacuum reservoir in the trunk, and about four thousand feet of vacuum lines running all over the car.

Also, for some unknown reason, most of the vacuum lines throughout the car are made out of a semi-hard yellow plastic. After a number of years, the plastic becomes brittle and cracks or outright breaks, especially in the corners where the lines feed into the doors (and therefore have to flex every time the door opens or closes).

The mechanisms in the doors that cause the doors to lock and unlock are prone to failing. They each have two (or four?) little rubber diaphragms that will eventually rot and split, causing loss of vacuum. I've found that these seem to fail all at once, or thereabouts. I've replaced three of the four of mine over the past three years, and have a spare ready for when the fourth fails.

If the lock in your doors only work intermittently, or only work while the car is running, or will only work once, immediately after you shut the car off and get out, then you've got a vacuum leak. Generally, it's one of the following: a leak in one of the vacuum lines (semi-likely), a leak in one of the vacuum-powered door lock mechanisms (very likely), a leak in the reservoir itself (very Unlikely), a failing vacuum pump (very Unlikely, and knock on wood that this isn't it).

While the car's running, you probably won't have any vacuum problems. The vacuum pump is powerful enough to generate enough vacuum to overcome small leaks in the system; when the pump is not running, the vacuum pressure will (relatively) quickly dissipate because of the leak, and you'll have problems such as doors not locking.
If you're the type to want to fix this yourself, you'd be well-advised to invest in a few tools to aid your battle against the vacuum system: - A small air vacuum/pressure meter - a hand-held vacuum pump - some rubber tubing of the appropriate size (Note: a kit containing all of the above can be had from IMPCO for $60) - some wooden golf tees. The golf tees are for sticking into the end of a piece of rubber tubing to seal off that section of the vacuum line from the rest of the system. It works!

The first thing to check, and generally the most likely cause of the problem, are the vacuum-powered door lock or trunk lock mechanisms. Here are some diagnosis steps (do all three):

A. Sit in the car with the doors unlocked and the car running. Do the doors lock and unlock properly? Does the trunk lock and unlock properly? If there is one door (or trunk, or fuel-fill cover lock) that does not work at all, even with the car running, then you've got a huge leak in that area and should be able to find it relatively easily. If it's a big enough leak, you may even be able to hear it leaking. If this is the case, then you should do a little happy-dance because it's rare that finding a vacuum leak is that easy.

B. Sit in the car with the doors unlocked and the car running. Shut off the car and wait for a minute or two, then lock the driver's door. Do the rest of the doors/trunk lock? If the other doors don't lock, then the leak MAY be in one of your many unlock lines, or in the unlock side of one of the locking mechanisms. This test alone doesn't tell you much.

C. Sit in the car with the doors locked and the car running. Shut off the car and wait for a minute or two, then Unlock the driver's door. Do the rest of the doors/trunk unlock? If the other doors don't lock, then the leak MAY be in one of your many lock lines, or in the lock side of one of the locking mechanisms. Again, this test alone doesn't tell you much.

Now, with the data you got from tests B and C, you should be able to figure out roughly where your leak is.

Case 1: If both tests B and C failed (i.e. no locking OR unlocking after a few minutes of the car being off) then it's most likely that the vacuum leak is somewhere else in the system besides the door locks. There are other systems in the car that are also controlled by the vacuum. Engine shut-off, brakes, climate control ductwork, probably more. I've never had a problem with these systems, though, so can't really be of any help here. (okay, well, I DID have a problem once where, while doing an oil change, I accidentally clamped some vacuum lines under the cover for the oil filter canister, but that's an unrelated story)

Case 2: Test B fails, but Test C succeeds. After shutting off the engine and waiting for a few minutes (doors locked), you're able to unlock the doors, but then can't lock them again; after shutting off the engine and waiting for a few minutes (doors unlocked) you're not able to lock the doors.

While sitting there waiting with the doors unlocked, there is constant vacuum to the Unlock lines (and the Unlock side of the locking mechanisms); your vacuum reservoir quickly empties due to a leak in one of the unlock lines and you're unable to lock the doors because you've got no vacuum.

While sitting there waiting with the doors locked, there's constant vacuum to the lock lines; since there is no leak, your vacuum is reserved. When you unlock the doors, as soon as there is vacuum to the unlock lines it is expended by unlocking the doors and leaking out the leak. You can't lock the doors again because there is no vacuum in your reservoir.

Case 3: The exact opposite of Case 2. Doors stay locked; you can't unlock them because there is a leak in the lock lines and no vacuum pressure.

Now, for actually finding the leak! I realize this is a long, long process, but the vacuum lines are really obnoxious to work on. I'm going to assume that you did all the tests and came up with Case 2 as your problem. You need to find and fix a leak in the unlock lines.

If there is one door (or the trunk) that seems to unlock more slowly than the rest, start checking there first. You should find two vacuum lines running to each locking mechanism, one for vacuum-lock and one for vacuum-unlock. In my car they are yellow with red stripe and yellow with green stripe, but I can't remember which is which, sorry.

***Method to narrow down your search: This is correct for my 240D, but may be different for other models.

You can find the vacuum lines for various parts of the car running underneath four floor mats. Pull out the floor mats, then the sub-mats, and you'll be staring at the metal bottom of the car. There are plastic covers that protect the vacuum lines (and some electrical lines? can't remember). These can be pulled aside pretty easily and you'll find the yellow vacuum lines. Search around until you find a rubber connector in the vacuum line; there are probably several Y-shaped splitters.

Disconnect these (**REMEMBER where they all go!) and seal them off With your rubber tubing and golf tees. Now go repeat tests A, B, and C (as described above) and see if you've made any difference. If some of the locks work properly and your vacuum is reserved, then the problem is in a section of the line that you've disconnected from the rest of the system. You've just narrowed down your search significantly.

Repeat as desired until you don't have any more places to disconnect and seal off, or until you've narrowed your search enough to start checking out one of the doors or the trunk.

***Examining the vacuum-powered lock mechanism. These WILL fail sooner or later, so go ahead and check them out.

For the trunk, it's essentially the same steps as for the door, but the mechanism may be locked in a slightly different place, and you have to know how to take the rear wall of your trunk apart.

For the door: Take off the door panel and disconnect all electrical lines (power windows, speakers, etc. You should have a thin sheet of plastic covering the metal door frame; GENTLY pull it aside (you'll need to reattach it later with some spray adhesive). Inside the frame will be the window hardware and (voila) near the bottom, the vacuum door lock mechanism. It looks like this (side view):

thin metal rod to door lock knob

two _ | _ vacuum | -+- | lines -> =====|_____|

It'll probably be black or blue plastic with a lot of rubber parts on it, and will be bolted or screwed into the metal door frame. It's easier to work with if you take it out, but getting it back in is sometimes a pain.

Disconnect both vacuum lines but **REMEMBER which is which!!** Mark with masking tape if you have a bad short-term memory. Use your rubber tubing and golf tees to plug the end of these lines.

Two routes of diagnosis, both useful and easy: Method #1: easier but less information. With those two vacuum lines sealed off, go crank up the car again, give It a few minutes to depressurize (vacuum-ize?) the vacuum reservoir, then shut it off again. Try locking and unlocking the doors. If they work properly, then you've found the problem to be that locking mechanism. Call your dealer or IMPCO and get a replacement. (I managed to find TWO Working replacements in a junkyard! yahoo!)
Method #2: More work but more information. Connect your vacuum hand pump to one of the vacuum inputs for the lock mechanism. Pump it and see what happens. Now plug it into the other one; pump it and see what happens. Make a thorough visual inspection of the two rubber diaphragms on the top of the mechanism; if these are cracked, rotten, or split, then that's probably your problem; the vacuum will leak out from the broken part of the diaphragm.

If the locking mechanism seems to lock and unlock properly (alternating the hand pump between the two lines going in), and the rest of the car shows no improvement with these lines disconnected and sealed off, then.. well, you didn't find the problem yet. Sorry.

Now to check the yellow plastic vacuum lines:

If you had sealed this part of the vacuum line off from the rest of the system, then it's entirely possible that the yellow plastic vacuum line is cracked or broken.
If you've got the hand pump and the vacuum gauge (or if you have a hand pump with a gauge built in), then examining the individual lines is pretty easy. If you don't have both of these tools, then it's next to impossible.

Connect the gauge to one end of the line (probably the end that's in the door, the end that you disconnected from the locking mechanism). Now go scrounge around in the floorboard and find the other end of the same line; it's one of the ones that you sealed off from the rest of the system. Connect your hand pump to this end of the line.
Pump it up enough to achieve a good vacuum, then see if the vacuum leaks out. If you can't get any vacuum at all, then the line is either completely broken or you put your gauge and pump on different lines (oops). If you get a good vacuum and it stays, then the line is good. If you get a good vacuum but then it leaks out slowly, then you've found the leaking line.

If you find a line that's leaking, you've got two options: replace or repair. Replacing the line will be more expensive and more work; repairing it is probably just as good (explain in a minute) but cheaper and possibly less work.

If you want to replace the line, you have to first go get a new piece of vacuum line (make sure you get the right color), then pull out the old line and pull the new line through to the right place.

If you want to repair the line, first find the section that's leaking (listen for a hiss? visually inspect?), cut it completely in half, and slip a piece of rubber tubing around it. Now, this may be more reliable, especially in a place like the door jamb, where the line has to continually flex back and forth anyway. The rubber will flex more easily than the plastic tubing.

======== OR! the REALLY easy way ==========
If you don't want to deal with all this, just drive your car to the dealer and say "I've got a vacuum problem, please fix it." They'll either repair it for you (for a modest fee, plus your first-born child) or they'll happily escort you off the lot, because they don't want to go through all this trouble either.

Hope this helps.
- Nathan '83 240D, 241,000 miles, and a working vacuum system