Door locks faling in 1984 300TD

Hi,
The door locks have become "flakey" and the engine shut-off has started having thoughts of its own, as well. By "flakey" I mean only one or two of
the five will lock after a minute or so and none will unlock. I understand these are symptoms of a vacuum leak. I've checked the hoses at the brake assist and found one black one that went through the firewall and then just stopped in mid-air with no connection point for it anywhere in sight. I can't find anything to account for the problem under the dash and next I intend to isolate each door actuator from the system to see if there is a leaking diaphragm somewhere. I feel like I'm literally grasping at straws.
Where is the best place to start looking? I am hoping that this is something that happens at some particular point in the system the vast majority of the time.
Is it the vacuum tank or a door lock actuator? Possibly the brake assist? Is there something that "usually" is the reason for this problem?
Thanks very much in advance,
Ken
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You don't have a manual do you?
There's a big fat vacuum line that goes from the vacuum pump to the brake booster.
Off this there's a tap for the transmission and EGR which go by way of the vacuum control valve on top of the injection pump.
Another line goes to the shutoff valve at the back of the injection pump.
On a 123 another line taps off and does the locks; on 126's this is not there, the locks are run by a vacuum pump.
There will be another tap to do the HVAC switchover valves.
In all likelyhood one of the rubber connectors has failed by loosening up or cracking. Sometimes you can fix this by cutting a 1/4" off and just sticking it back on. If it's the weird L shaped connector on the shutoff valve you can usually just take it off and swap the ends around and it'll be ok.
I went throgh this last winter and took a few pics and made some diagrams. If you have any qiestions jsut ask.
http://viewimages.mbz.org/by_chassis/Sedan/126/parts/vacuum /
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Kenneth
The black line that goes nowhere is a vent line. Rather than have the vacuum system vent in the engine compartment, where dirty air could enter the system, the line runs into the cabin area under the dash where the air is cleaner. So when the vacuum system vents, (that is, when it sucks air into the vacuum lines) it draws in clean air. You don't have to mess with that black line. It's OK just like it is.
Most likely your problem will be one of the door lock controls. You really need the manuals (I have the disks) to locate all of the lines. But, to get you started, lift up the passengers side floor mat. On my '82 123 300D, there is a black plastic cover that is held down by a screw. Remove that and you will have access to the vacuum lines that run to the other doors and the fuel flap door. Use a hand vacuum pump (about $35) and test the lines. The door locks work by vacuum both to lock and unlock the doors. Pump one line and the locks go down. Pump the other line and the locks come back up. On mine, I suspected the right rear door, but I was wrong. It turned out to be the fuel door. It would not unlock. I bypassed the module and now everything else works. The engine stops when I turn off the switch, the doors lock and unlock, the trunk locks works.
The disks are available on ebay or from MB direct. Mine came straight from Germany. Well worth the money.
Larry In the back yard, under the oak.
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There's several major branches off the main vacuum; locate and plug up the locks vaccum branch and take them out of the equation to see if they are somehow the source of the problem.
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Richard said ... "There's several major branches off the main vacuum; locate and plug up the locks vacuum branch and take them out of the equation to see if they are somehow the source of the problem."
That's very true. However, with no diagrams to go by and you're new to this problem, under the carpet is the simplest and easiest test point for what is most likely to be the source of the problem.... one of the door locks. If you believe in the odds, then the problem will most likely be the drivers door where the tube runs through the hinge opening. But to get to that connection, you have to stand on your head in the drivers foot well looking up under the steering wheel after you have removed the lower dash cover and the side kick panel. Don't forget to hold the flashlight just right. What I told the newbie was to unsnap two snaps, remove a screw or two, and damned if it ain't right there in front of ya! And easy to work on, too. When you find out which line it is, ya just plug a golf tee into it. Then ya fire her up and see what that did. If'n ya don't like the results, ya pull the golf tee out and put the line back. Then ya try a different line. Easy for a newbie to do. And if it turns out to be the drivers door, then he gets to learn how to take the door apart. But that's a different weekend. I digress.
Larry In the back yard, under the oak.
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hmm... all this has me thinking, always a dangerous situation. I have a 300e, 1994, bought used with 160,000 miles on it, and the driver's door works with the key, but the others work all together. For example, if the car's locked, I can open all of the doors by using the key to open the trunk, or the passenger door. This also locks them all, too. Except once in a while the driver's door doesn't unlock from the truck. Unlocking the driver's door, or locking it, has no effect on the other doors. I assumed this setup was standard, but now I'm not so sure. Is the driver's side lock, supposed to open the other doors the way the passenger's side lock does? And if so, is the same panal and screw under the carpet on the passenger side of a 300e? I know, I know, "get off your ass and go look."
Thanks,
Sammy
Toolbox contains one bent phillips screwdrive and two golf tees.
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Sam I have no clue how your 300e works, especially one that is twelve years newer than my '82 300D. I can only tell you how mine works. When I lock or unlock the drivers door, it controls everything else. Doors, trunk, and fuel door. I can over ride the trunk lock while the rest of the car is locked by inserting the key and turning it counter-clockwise. Not quite a quarter turn to the left. Then push in and the trunk opens. I can also lock the trunk by turning the key clockwise a full quarter turn -- 90 degrees -- and remove the key. When you push the button, it only goes in but does not release the lid, regardless of whether the rest of the car is locked or unlocked. Only the square key -- master key -- will open it after being locked in this manner. The round key -- chauffeurs key -- will not unlock the trunk or glove box.
I would think your car would function much the same. My system works on vacuum and the drivers door contains a multifunction valve mechanism that controls the switching. After my car sits overnight, the vacuum leaks down to zero. So when I unlock the car in the mornings, only the drivers door unlocks until the car is running and the vacuum builds up.
I have the CD's for mine and they have proven to be worth every cent. I paid about a hundred bucks direct from MB. The diagrams are both good and bad. They are great when I can see them, but they are terrible scans of the original manuals. The electrics are almost worthless. Still, you need the CD's.
Larry In the back yard, under the oak.
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By the way, you're in luck. The screws are phillips head.
Larry In the back yard, under the oak.
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With the European models the driver's door is the master, which locks and unlocks all the other doors. The boot (trunk) lock is not part of the central locking AFAIK in the 123 series. American specifications may be very different, certainly insofar as the trunk is concerned.
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Hi,
First off, a heartfelt "THANKS!!!" to everyone that responded. It was all very, very helpful.
Second, what an amazing pain in the arse! Like looking for a leaking water pipe without the benefit of a puddle.
Turns out it was the passenger door vacuum element. One side. I mean, it leaks going one way but not the other. How can a single diaphragm do that? Why have more than one diaphragm?
The method that I settled into was to find those junctions under the front floor mats, attach a hose to each line in turn and create a vacuum (something I picked up from nursing, I suppose) and then trace down the "bad" line to the offending component. Some of the "quadrants" have enough volume to fool you, though. Plug the hose with your tongue an wait a minute.
The most impressive result was the change in the performance in the car:
1. The transmission shifts more firmly where it had been a little soft before and definitely "not right" between 2nd and 3rd. 2. The engine shuts off IMMEDIATELY when the ignition is turned off. Used to lag a fraction of a second. 3. The brakes are definitely more responsive to pedal pressure. 4. The damned cruise control came back to life. 5. I may be fantasizing, but the car seems overall more "perky" somehow, which is something I wouldn't ordinarily say about a diesel.
I would never have guessed that a just a _reduction_ in vacuum could have so many symptoms..
Of course the door locks work perkily now. And I can take off an interior door panel in about two minutes. Back on in three. So I guess I'm perky now, too.
Well, there it is. Thanks again for the input.
Ken

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