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  #1  
Old 04-04-2000, 02:19 AM
MikeTangas's Avatar
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Location: So. Cal
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The central locking system on my 73 280 SEL stopped working for the passenger side. I determined that the actuators for both passenger doors have holes in the diaphrams, apparently from the lower portion of the window hitting the diaphrams when rolled all the way down. I have ordered replacement actuators and will be installing them as soon as they arrive. In the course of checking out the system I determined the following:

1. With everything hooked up, engine running, the system would pull approx 10 inches Hg.

2. System would bleed off all vaccum from the resevoir within 20 seconds once the engine was shut down.

I believed that the bleed down was due to the bad diaphrams and took the vaccum test a few steps further. Found that the system will:

1. Pull 15 inches Hg with the engine running at idle and the vaccum gauge attached at the check valve, with last leg of the "T" plugged. Hold 15 inches Hg after 15 minutes of with engine shut down. Check valve good.

2. Pull 15 inches Hg at the first "T" with the leg to the cabin plugged. Resevoir tank held 15 inches Hg for 15 minutes with engine shut down. Tank Good.

3. On all night resevoir test, tank held 15 inches Hg for 14 hours, no decernable drop in vaccum. Tank in great shape for 27 years old.

Now for the questions.

Would the bad diaphrams allow for a drop of 5 inches Hg while the engine is running?

Which door do the trunk and fuel door locks operat from? I know the driver's button operates the vaccum switching, but do the trunk/fuel door lock lines come from the right rear?

Also, how many vaccum lines should be running to the fuel door latch? Mine only has one (yellow or off white) which has been capped. The fuel door latch had a 180 degree bent rubber line, which someone cut, coming off the top of that actuator. They then put the cut-off on the lower side of the actuator, leaving it open to atmosphere at both ends. I'm thinking, being at the end of the line so to speak, the fuel door only had one line, the vaccum supply to activate the lock. When the vaccum is removed, atmosphere allows the latch to retract. Am I right?

And lastly, for now, when in the door panel, I hooked up the vaccum gauge to the supply line at the actuator. When teh driver's button was pushed the gauge showed about 1 inch Hg draw. Is that sufficient to cycle the actuators?

I know this is lengthy, but no one has been able to help me yet. With nothing to figure things out, other than what I can surmise from the layout of things, I have tried to explain my finding to the best of my ability.

Thanks to all.

------------------
Mike Tangas
73 280 SEL
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  #2  
Old 04-04-2000, 09:27 AM
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Now for the questions.

Would the bad diaphrams allow for a drop of 5 inches Hg while the engine is running?

Absolutely!

Which door do the trunk and fuel door locks operat from? I know the driver's button operates the vaccum switching, but do the trunk/fuel door lock lines come from the right rear?

The two systems "lock" and "unlock" are like a tree. The lines branch off for each door and element down the right side. The left rear door is the first branch before the system passes across the dash. (I presume we are talking a 108 chassis here). The lines go along the inside sill moulding eventually going into the trunk.

Also, how many vaccum lines should be running to the fuel door latch? Mine only has one I'm thinking, being at the end of the line so to speak, the fuel door only had one line, the vaccum supply to activate the lock. When the vaccum is removed, atmosphere allows the latch to retract. Am I right?

Sort of. The gas flap has one line because it works against a spring. The spring moves it to the opposite position when the vacuum goes away.

And lastly, for now, when in the door panel, I hooked up the vaccum gauge to the supply line at the actuator. When teh driver's button was pushed the gauge showed about 1 inch Hg draw. Is that sufficient to cycle the actuators?

The further down the tree you go the more your vacuum is going to look like the problem than the source. No 1in isn't enough. The technique you used in vac testing at the source was appropriate. Now you must take it the rest of the way.

The first step (this holds for all two line "vacuum only" systems)is to identify the resevoir line. After verifying that it is tight (as you did) disconnect and plug the line to the reservoir. You want to tee into the line that goes to the master switch (the other line under the hood) and monitor the system without the reservoir (this magnifies the visual effect of the leaks - they are easier to see). Try both lock and unlock to see if the leak is in only one side.

Then approach the side that leaks the worse. On 108 chassis the lines were available through the removed glove box; you can cut and reconnect with rubber if no junction is found. Disconnect and cap. This removes the whole right side. Verify the tight system. If there is still a leak check master valve or left rear door. If there is no leak, reconnect the system and go to the trunk, disconnect and cap the incoming line. Does it still leak. Cap off every leak as you find them and keep eveluating untill you have no leaks.

The later cars have all the junctions available by removing either carpeting or sill covers, but that old car is probably harder to get to the junctions than to remove both right side door panels.

Besides, I recommend replacement of the vacuum door servo in bulk, especially if you are paying for the diagnosis. The problem with just fixing the one that is bad is: because the system has been running at lower levels of vac when the system is restored the rest often fail quickly under the new load requiring further diagnostic costs and eventual replacement anyway. Because of the ease of diagnosis and their different evironment the trunk elements don't need to be incuded in this bulk replacement.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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  #3  
Old 04-04-2000, 09:17 PM
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Thanks for the quick reply. As far as the question about which door operates the trunk/fuel door, I must have been tired, I meant which door do the vaccum lines run from. But in reading your post, that question is answered.

You are correct, it is a 108 chasis.

I will re-run the tests preformed once I have installed the new actuators. As I think about it, it is very possible that the bad right rear actuators could have affected the vaccum reading at the right front since the "T" to the rear door would be before the front door actuator. Slowly this vaccum system is making sense.

I will follow the remainder of the described procedures as well. I feel good that I was at least close on the workings of the system, given all I had to work with was the car, my tools and a vaccum gauge. No manual and no one else around my neighborhood has a 108 to look at.

I am doing my own diagnosis and labor, so for me the only outlay is parts. The prior owner stated that the left side locks had been repaired several months before I bought it. No receipt on that so I am not sure. The master valve in the driver's door does apper to be in near new condition so it is possible. Also, so far, all the rubber connectors appear to be in very good shape, still pliable, no cracks or tears, haven't found a brittle connector yet.

Hopefully the new actuators will be in before my next days off (Thurs/Fri) and I can post the results when the work is completed.

Again, thanks for the assistance.



------------------
Mike Tangas
73 280 SEL
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  #4  
Old 04-05-2000, 11:00 PM
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Join Date: Sep 1999
Location: montreal,quebec,canada
Posts: 53
i have a 300d 123 body.
95% of the time the vacuum is ok but once in a while the engine keeps running on due to loss of vaccuum.
any ideas what could be the problem with the vaccuum circuit.
thanks
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  #5  
Old 04-06-2000, 12:37 AM
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Join Date: Apr 2000
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About everything I currently know about the diesel shut down is what I have read, no 'hands on' experience, but since I hope to own a 300SD by the years end I do read up on them.

If your engine isn't shutting down it is vaccum related. You have a vaccum leak somewhere in the system that is certain. The leak could be in the door lock actuators, the ignition switch, possibly the climate control panel, or the engine shut down device. This is inside the injection pump, it is a vaccum actuated bellows that pulls the fuel rack to OFF when you turn the key
the OFF. The bellows wear out and/or get oil logged and you see the result. There should be a brown vaccum line attached to the shut down device. If the bellows have been saturated with oil, possibly the vaccum line has oil in it as well which may cause it to be plugged.

I would start with the central locking system as it seems the easiest, and work your way to the injection pump. According to all I have read, it would be best to let a MB mechanic replace the bellows in the shut down, if that is where the leak is. I gather that if done incorrectly, you may cause he engine to over rev, and have no way of shutting down before you destroy the engine.

Again, this knowledge is not hands on MB diesel experience, it is from reading and learning. Hopefully it is close enough that the techs and experienced MB diesel mech can elaborate and help out further.

To qualify my diesel experience though, I used to (20 years ago) be a Detriot Diesel mechanic while working in the offshore oil field.



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Mike Tangas
73 280 SEL
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  #6  
Old 04-07-2000, 11:35 PM
MikeTangas's Avatar
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Central locking system now working.

I spent the day replacing that bad actuators and tracking down leaks. A fair amount of the connectors had become brittle with age, so I replaced all I could reach.

I could not decide how to remove the glovebox liner without causing damage, so I opted to pull the kick panels instead. I was able to access the junctions in behind the panel. Although it was tight, I was able to do it.

I still have a small leak to track down though. When I last did the all night test of the resevoir and check valve, everything was great. After finishing today, vacuum was bleeding off ever so slowly, and it looks like the check valve is going south. I can pull the valve, shake it replace it and it will hold again. I'm replacing it tomorrow, and we'll see how things are looking then.

Thanks for the assistance and pointers.

BTW, the trunk is locking just fine, I still have to hook up the fuel door latch, hopefully it'll be fine too.

Again thanks.



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Mike Tangas
73 280 SEL
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