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  #1  
Old 01-03-2004, 06:00 PM
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Central Locking System

Is it just my imagination or is the whole vacuum operated central locking system an ongoing PITA. Mine has a slight vac leak (which I am going to get to soon) and as a result, everything locks OK and will unlock again as long as it is not longer then 45 minutes.....then I have to start the car to unlock the other doors and trunk. So, I have to ask.....in typical car, how long should the vac hold?

My next thing, is to look at changing the system ala the 126 with a little vac pump dedicated to the locking system. It's almost as though our cars were an experiment that MB found didn't work very well. I am thinking that a pump from a 126 (or ?) and connected into the locks via a vacuum switch....say around 15" should work quite nicely. Might even eliminate the resivoir tank as well. Let the pump stay hot at all times so that even with a sight leak, it would cycle for a couple of seconds or so while maintaining vac. If one wanted to be creative, one could put in a low voltage relay that cut the system out at 11.5 V or so.

Any reason why this shouldn't work......plus it would be invisible.

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Litton
'90 420 SEL (sold)
'72 280 SEL 4.5
'98 ML320 (for sale)
'86 560SL
'05 Jeep Grand Cherokee Ltd (offroad in style)
'87 Chevy Blazer (AZ Pin Strips)
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  #2  
Old 01-03-2004, 06:19 PM
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"It's almost as though our cars were an experiment that MB found didn't work very well"

Yea, after all its only 32 years old. Look how long the pyramids lasted.

If they had used motors like most other manufacturers, they would have been a lot more money and they would have been lucky to last a decade.

The vacuum elements aren't going to work with a single line type system and will have to be replaced anyway as they are whats leaking. Do you think that 126 pump has more life than your engine (your vacuum source).
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  #3  
Old 01-03-2004, 07:53 PM
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Steve, thanks for the info on engine life vs pump life and the longiviety of the pyramids. But I think you misunderstood my meaning. Vacuum is extremely difficult to store and such storage is very maintenace senistive. Even more so in a dynamic system. That's what I think the MB engineers realized and then went to a pump instead of a storage vessel. Also, part of my question was "how long should the vac hold"

Now it's my turn to not understand. Why the pump would not work in a single line system if all you are replacing is the souce of the vacuum. I wasn't thinking about modifiying anything except hooking the pump into the line going to the left front door.
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'90 420 SEL (sold)
'72 280 SEL 4.5
'98 ML320 (for sale)
'86 560SL
'05 Jeep Grand Cherokee Ltd (offroad in style)
'87 Chevy Blazer (AZ Pin Strips)
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  #4  
Old 01-03-2004, 08:51 PM
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The W126 system uses a single pump that runs in two directions to provide both vac and pressure, and is electronically controlled. Not a good replacement unless you want to convert over completely, and that is probably more work than getting what you have to work properly.

Three are three things I'd look at first:

1. Check valve in engine compartment. If this is bad, vac leaks off. 45 min is way to fast, it should hold for weeks.

2. Cracked line in driver's door -- the main supply line runs here, and gets flexed every time you open the door.

3. Vac switch on driver's door -- these wear out and leak.

Go and get a MitiVac. REmove the vac line at the check valve and pump down. If it holds, the check valve is bad. You can also test this by pulling the line to the tank in the fender and pulling down -- bad chekc valve will hiss, and the vac leak will stop when you cover the other end with your finger.

If it still leaks, then remove the driver's door panel. Detach the lock and unlock lines from the door switch and check each one for leaks with the Mitivac -- doors should all lock and unlock smoothly, and each half of the system should hold vac indefinitely. If one side leaks, you will need to chase down the bad part (almost always a bad diaphram in a door or trunk element. The gas filler door is lock only, unlocks with a spring.

If both sides hold, apply vac to the switch after removing the yellow line and reattaching the others. If the switch leaks, replace it.

My locks work perfectly now that I replaced the bad section of line in the engine compartment. Not bad after 32 years.

Peter
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  #5  
Old 01-03-2004, 09:02 PM
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The 126 pump system uses one line with vacuum one direction and pressure the other. Your system uses vacuum in both directions using TWO lines. I seriously doubt that the vacuum elements in your car could be made to function off pressure.

Non leaking systems hold vacuum indefinitely, days, weeks maybe more. The key to quick diagnosis is to remove the reservoir from thye system and put your gauge there. Without the reservoir the leaks are seriously amplified and can easily be seen on the gauge.
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Old 01-03-2004, 09:11 PM
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Well, having gone through this so many times myself, I can probably provide advice (or so I hope!)

What I did was disconnect the "T" and hooked the source line directly to the line going to the driver's door (bypassing the tank), because the tank takes a VERY long time to pump up and holds the vac longer, making it harder to detect a leak. First I actually checked the tank alone - vac pump connected to my tank held 15" of vacuum overnight with no drop off.

Then I checked the easiest spot for me to get at - the trunk and gas locks. On the RH inside of the trunk there is a plastic piece (oblong about 4" long 2" high) that covers the "T" line going to the trunk lock and the gas lock. I tested the trunk and gas locks individually (my trunk one was the source of my leak!) and then tested them together further up - the line runs along the RH side (under a plastic piece, if yours isnt cracked/missing, mine was). I cut the line here and tested it, then reconnected it (Oh, so you know, go to the auto store and pick up 2-4' of vac line for under $1 usually, it goes a long way - cut 3" pieces and replace all the old rubber ones).

Then I checked the entire system again, and it was vac tight. If yours isn't though, take your LF speaker out and take the molding off the side (A real PITA - it's clamped in well). There is a "T" in there where the line goes from the switch in the door to the LR door and the other to the R-side doors, trunk and gas - since you checked the gas and trunk, if this leaks, it must be the right doors, if the other leaks, it is the LR door).
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  #7  
Old 01-04-2004, 09:29 PM
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I did the Mity Vac thing on the tank and the locks separately and found pretty much what you expect....tank hold great (lots of pumping to get to 20") and the locks leak. It hasn't been a big enough problem to tackle yet and will probably do it in conjunction with the regulator.

Also, thanks for the info that when the mechanics are in good shape the vac holds for a long period of time. Please excuse my skepticism when it comes to vacuum but I have had more experience than I wish to remember with high vacuum equipment on lasers and deposition equipment.
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'90 420 SEL (sold)
'72 280 SEL 4.5
'98 ML320 (for sale)
'86 560SL
'05 Jeep Grand Cherokee Ltd (offroad in style)
'87 Chevy Blazer (AZ Pin Strips)
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  #8  
Old 01-04-2004, 11:06 PM
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Litton:

This is MUCH easier than high vac systems!

The only real PITA is finding the bad part.

The vac lines run under the cover along the door sills (inside).

Most likely, if you have a leak all the time, not just when locked or unlocked, the door switch or the yellow plastic line is bad.

I personally thing the vacuum locks are simpler and more elegant than electric. Much better than hydraulic door closers in the 600 grand, too!

MB used them in one form or another from the early 50's, I think, to the latest models with keyless entry, when they changed to "Chyrsler" stlye electric.

Peter
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1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
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  #9  
Old 10-29-2005, 12:58 AM
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central locking pump / control unit

can anyone tell me where the central locking pump / control unit is located in a 1991 300 te station wagon please?
Cheers, Jaap
email: profoto@ihug.co.nz
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  #10  
Old 02-26-2006, 04:15 AM
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pump location

under the rear seat cushion (passenger side for LHD cars)
adam
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  #11  
Old 02-27-2006, 12:32 AM
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CLS System checks

Lots of good advice above - especially with regard to vacuum checks with hand pump - (if you don't already have one, can get a cheapie at most auto stores; consider getting one with the reservoir cup which enables you to do one-man brake bleeds, as well)

NOTE: "pulling" hard plastic lines out of connectors/hoses is usually counterproductive and may result in breaks/tears - the rubber tends to shrink/tighten when pulled upon - rather, hold the hard line and use a flat-blade screwdriver or similar tool to PUSH the rubber hose end off the end of the hard line...

Easiest initial access indeed at manifold "Gumbi's" - red to front reservoir, black to cruise control, yellow/grey to CLS front door switch/rear reservoir, blue to seat locks (coupes), green to climate control...
next at trunk unlock panel - yellow/red to "lock" trunk and T'd at gas cap lid;
yellow/green to unlock trunk (gas cap springloaded to unlock if "lock" released)

The connector rubber hoses and hard plastic lines are incredibly robust and long-lived - [EDIT] [the gas cap actuator is fragile and small and a suspect leak culprit]. If it is, it's a little awkward to reach - in my 280CE/E's, the mounting screws are, however, in a keyhole slot - just loosen and lift out (no need to unscrew them out).

You can see if there is any difference in leakdown while unlocked, as well as while locked.

If losing whilst locked, but not unlocked - I would check gas cap's actuator first. Both the gas cap's and trunk's are easy to access, and not nearly as robust as the door locks' bellows. [EDIT] [One] can also get at the lock and unlock hoses alongside rocker-side floor pan edges, as well as under the rear seat. [EDIT] [the hard lines are continuous from the firewall, but you can cut in and test, then splice, with hose.]

Pull up typical system in:
http://skinnerbox.steaky.org/Service/W123/Main.html
under M110, any similar model, such as 280E -
Chassis/Body Manual
Central Locking System (section procedures 80)
80-260 (troubleshooting/checkout)
80-900,901,902 (system diagrams)

{EDIT}
Litton, glad you've been able to isolate to doors; if you're limited in resources or stubborn, you can CAREFULLY dismantle the membranes or either side out of junkers and repair/replace a single torn ones' elements, but you still have an old membrane, and you probably love opening up doors as much as do I...also, if you find good used dual elements with different pull rods, you can judiciously PB-Blaster the rod end in the potmetal "bridge" and pop the rod out of the notch with channelocks. If replacing whole used elements which used different mounting holes, or new, recommend pre-threading the sheetmetal screws while out on the bench.
Also check replacement elements - I gather there are at least two versions, which may or may not be interchangeable.

Stan.

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Last edited by Tristar1959; 02-27-2006 at 03:53 PM.
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