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  #1  
Old 07-21-2009, 09:06 PM
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Location: rough and ready, ca (halfway between sacramento and reno
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newby vacuum questions

my daughter's newly acquired 1979 240 d will not let her lock the car if she waits more than a minute or so after turning the car off (locks won't go down). also, is there a way to lock the doors while driving? just got it and haven't had time to read owners manual or haynes manual that came with car. car came with a 5 cylinder (non turbo) and 4 on the floor if that makes a difference.

thanks in advance

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  #2  
Old 07-22-2009, 07:42 PM
meltedpanda's Avatar
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well it is all vacuum driven , you really just have to find the leak, common on that car is the multi function valve inside the drivers door. easy to R/R. first make sure the vacuum pump is working ( sounds like it is if they work , but leak down)
Only way to lock from inside is to push down drivers side lock, it will lock the others, or it should
Look in the DIY section of this forum, I think the R/R of the valve is there
If not PM me I have it.
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2015 Porsche Cayman - Elizabeth
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Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
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  #3  
Old 07-23-2009, 08:15 AM
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Once you track down the leak and get the system working, she can lock the car from the inside simply by pushing down the locking button on the driver's door and that will lock the other doors, the boot (trunk) and the filler cap.

Vacuum leaks are a very common fault - it's worth investing in a vacuum pump with a guage (such as a mityvac) as it will pay for itself in one use. Also buy a bag of golf tees for blocking the vacuum hoses.

The following relates to tracking leaks in a w108, but the principle is the same in other models.

How the system works. The whole systems sucks (joke). When the engine is running, the engine manifold (or in a diesel a special pump) creates vacuum and sucks air out of a small plastic reservoir tank which 'stores' vacuum for use next time you lock or unlock the car. If the system is working properly, you should be able to lock and unlock the car about 10 times before the reservoir runs out of vaccum and you have to run the engine again.
The vacuum reservoir is linked to the other 'actuators' (the devices which lock and unlock the doors etc - see attached photo) with plastic lines joined with rubber hose. A yellow plastic line connects the vacuum reservior to a main lock in the driver's door. A white plastic vacuum line from the main lock locks the car by creating a vacuum in the top diaphragm of the actuators (one each on the passengers door and the rear doors, the boot and filler cap), which then goes concave, and pulls down via a rod on the locking lever. A black line from the main lock opens the locks by creating a vacuum in the bottom diaphragm of the actuator, which then goes concave, and pushes up on the locking lever. Simple, elegant, quiet, robust and effective, as long as it is airtight. Leaks can be in the actuator diaphragms, or in the rubber boots or t-joins that join the plastic tubing.

The leaks are usually in the actuators. The actuators are at the bottom of the doors, adjacent to the central door posts of the car. The easiest one to get to is in the front passenger side door. If you look at this, run the car engine while locking and unlocking the driver's door, the whole system will start to make sense. Remove the door liner and you will find it near the bottom of the door. You may need to peel back a clear plastic liner to view it. Test your actuators by blocking one of the hoses into the actuator with a golf tee and suck on the other hose with your vac gauge. If it does not hold a vacuum, you have found a leak.

If all your actuators are fine then consider other culprits.

The main lock on the driver's door which controls the whole system may be a source of leaks. Start by removing the liner on the driver's side front door. You will see the little metal or plastic valve which controls the whole system. Test this with your gauge.

A leak in the locking system is more of hassle than a leak in the unlocking system, because the vacuum locking mechanism needs to hold its vacuum for hours. If it leaks, the res. empties (or strictly speaking it fills), and then there is no vacuum to power the unlocking circuit when you turn the key. Voila, the central unlocking fails, and an opportunity to impress your passengers evaporates. I have heard that the top (locking) diaphragms are generally the problem, or the main lock on the door. In my case the main leaks were both on the top diaphragm.

The whole system is powered by vacuum (at about 15inHG), and thus it is also possible that there is a leak between the manifold and the vacuum reservoir, but if this was the case, both locking and unlocking would probably only work when the engine was running. If you have no vacuum at all in the res when the engine is not running, then the cause might be a leak between the manifold and the res., or the non return valve to the manifold. is shot, or the res. itself, or the (yellow) line between the res. and the main lock, or the main lock itself. Again, your gauge can help work out what's wrong fairly quickly.

While you are testing your actuators, it also makes sense to test the lines between the main lock and the rest of the system by attaching the gauge to the white or black lines from the main lock, and blocking the lines at the actuators. Then you are only testing the lines, not the locks or the actuators. If the lines leak, you probably have a leak in one of the joiners, as the plastic lines themselves are extremely tough and durable. The lines leading to the boot/filler actuators can be found under an oval cover on the inside of the lower sill of the boot.


Hints -
Start with the most likely problems - holes in actuator diaphragms or the driver's door locking valve.
Keep records of what you do as you test each part of the system. It saves you retesting and helps you with your detective work and gives you a sense of progress. Work through the whole system systematically.
There can be more than one leak, so test the whole system even if you initially find one leak.
If you think you have found a faulty part, remove it and 'bench test" it several times with the gauge. No point in replacing something that is ok especially as the parts are not particularly cheap.
Buy some joiner hose from the stealership and replace each joiner as you find them - you can then eliminate joiners as the source of the problem. You can get enough hose to replace all the joiners for about $20.
Use the opportunity to clean down your door liners with warm water and spray the inside of the doors with fish oil or similar.
Attached Thumbnails
newby vacuum questions-actuators.jpg  
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1980 300D

Last edited by ABDow; 07-23-2009 at 08:51 AM.
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  #4  
Old 07-24-2009, 08:37 PM
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Location: rough and ready, ca (halfway between sacramento and reno
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thanks. i downloaded a diagram of the vacuum system, but having the process will be helpful.
while i have you, her key stopped working in the ignition. she just now told me that it has been getting worse. first it wouldn't work, she would wait a few minutes, go back and try it and the key would turn. today she got stranded and when i got there i tried everything i could think of but still couldn't get the key to move. rattled key, moved steering wheel, turned key over. any ideas?
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  #5  
Old 07-24-2009, 09:31 PM
meltedpanda's Avatar
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Location: Central Ky
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probably just needs a new tumbler, easy to replace and can be ordered by VIN thru MB dealer, get key as well
pretty common
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Ron
2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace
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  #6  
Old 07-27-2009, 06:19 PM
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It's now no longer necessary to buy the entire actuator. You can get the rubber diaphrams alone, which are what go bad. The body of the actuator is almost never the source of a leak. So if you are going to rebuild one actuator, you might as well do all 4; They're all the same age. However, the last time I replaced all my diaphrams (year 2000), there was no simple diaphram available for the trunk or gas filler door actuators. Maybe now?
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  #7  
Old 07-31-2009, 08:40 AM
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Location: Adelaide South Australia
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Ignition and steering lock problems are not unusual in w123s. My daughter's 300D had a very worn ignition key and lock and we replaced both with good results. You could try just recutting the key. Steering locks are more serious as you can find yourself with a car with steering that you can't turn. If the steering lock starts to get sticky, it's worth getting it fixed before you end up with a car that you can't start or steer.
In order - have the key recut, if this does not work have a new key/tumbler fitted.

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1980 300D
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