I was doing door maintenance and hoping to also cross off any culprits in my lock system leak - starting with driver's door in my 82 300D. When I unhooked the 3 lines from the master lock element I was able to get a solid vacuum hold on the right (where yellow with green stripe goes in), the middle (where plain yellow goes) but NO hold at all on the left-most port (where red stripe goes in). I was able to get a vacuum to hold by testing a port and plugging the other two ports.

Here is a picture of what I'm talking about:



When I pump on that left/red-stripe port I get no hold - likes the pump is hardly connected to anything at all. I'm assuming that this is NOT correct behavior and that I need a new element. But one thing I noticed is that I wasn't able to lock the door manually once I had all the lines disconnected. Is this port of the element not going to hold vacuum unless the door is in the locked position? Do I need to do more testing? Or have I determined this element is leaking at this point?

Followup question, when I look on pelican for this part - three with the name "Door Lock Vacuum Actuator, (Master Element)" come up.

One is an MB Part #: 000-800-10-73-M22 - and is $12.25
One is Siemens Part #: 116-800-04-73-M82 - and is $43.50
One is also an MB Part #: 116-800-04-73-MBZ - and is $91.50

The more expensive Siemens and MB ones look more correct in their pic/illustration - but what is that super cheap Benz part that has the same name but is suspiciously super cheap? It has a "Note: from chassis # 036517" appended, while the Siemens one has "Note: thru chassis # 036516" appended.

Can I tell if my chassis is compatible with one of them by the year or VIN? I'm already guessing that since the photo of the more pricey ones looks more similar to what's currently in my car, my question is answered - but I wanted to check before buying. I have a 1982 300D Turbo.

Thanks for any help.

__________________
Andrew
Montclair, NJ
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1982 300D Turbo
120k
Petrol Blue Green

Was the door closed when you tried to manually lock the door? The door will not lock unless closed. The line with the green stripe is the "lock" line, the line with the red stripe is the "unlock" line. The solid yellow line is the main vacuum source coming from the engine compartment. This solid yellow line should have a check valve in the line. Check this balve with your Mityvac to ensure that it is still operating as a 1 way check valve. You do need to do more testing as the problem may exist in the other 3 door vacuum door actuators, the fuel door actuator, the trunk lock actuator or the plastic tubing/rubber fittings running along the floors. It is common for the plastic lines to break/crack where they pass in the door jambs. Your picture is of the main vacuum actuator valve. There are two different valves. One is a full plastic valve and does not have the metal attachment bracket (the valve attaches to the inside of the door by sheet metal screws that go through holes in the plastic valve). The other, like yours, attaches by the metal bracket. As far as I know, they do not interchange. My 1983 300TD and 1985 300D uses the all plastic valve. I also have a 1982 300CD but have never had the door panel off so don't know which valve it has. I would contact Thomas.Hanson@mbusa.com for the proper part number. Tom is the supervisor of the parts department at the MBZ Classic Center. Ask for the club price, you may be surprised that his price is comparable to what you have found.

This is backwards from my understanding of red being lock (red means stop, green means go), from just having gone over my car (85).

Here's a guide I used when doing mine:

https://www.ifixit.com/Guide/Mercedes+W123+Vacuum+Lock+System+Diagnosis+Technique/20201

Mine turned out to be a few little things, but mostly the locks misbehaving was a torn tailgate lock actuator. Luckily I didn't have to go through each and every one. If you pull and plug the lines from the few things that are easy to get to first then you might have the same luck.

-Rog

fwiw your chassis # is the last 6 numbers of the VIN

__________________
1981 NA 300D 310k miles

My reference to red/green was taken from the diagram posted on this forum. Now that I think about it, the diagram may have had the colors reversed. If I could figure out how to post pictures on this forum I would post the diagram referenced.

yeah, thanks for that tip BWitmore. so I tested it with door closed and locked and it seems to hold vac. I know i have to test other doors/trunk, etc. - but I was hoping I may have found something wrong on the first door i tried! no such luck it seems.

so - where is this check valve in the main solid yellow line supposed to be? in the door, under the dash? I have the yellow valve in the engine compartment that goes into the firewall (splits to tank and driver door) - but I didn't see any other check valve on the line in the door itself. i can't be sure, but it didn't look like anybody had been in this door before... but if i had no check valve, then the system would likely not hold up after I shut the engine off. All 5 locks work great when system is running, lose charge after about 10 or 15 seconds after shutoff.

__________________
Andrew
Montclair, NJ
--------------
1982 300D Turbo
120k
Petrol Blue Green

The check valve in the door should be in the solid yellow line that goes to the middle port on the main vacuum valve.

yes - so I should be able to find this check valve inside the door cavity? its not somewhere else further up the line before it gets into door? when i turn the car off, i do here this high-pitch wheezing that peters out after 10-15 seconds (hey...), and its coming from somewhere behind the steering wheel area of dash. i assumed it could be anything, or AC pod related.

__________________
Andrew
Montclair, NJ
--------------
1982 300D Turbo
120k
Petrol Blue Green

I believe that's all it is, and probably isn't your problem, as I've heard that before, including on mine that's all fixed now.

If all is stock, the doors are actually isolated from everything else, and in fact you can unplug the yellow vacuum line under the hood and it should still hold its own vacuum if there are no leaks.

On mine it would hold a vacuum all day long if the doors were unlocked but as soon as I locked them it would loose all the vacuum within a few seconds. I imagine you could also have the opposite problem. If that's a symptom like yours then it's probably one of the actuators. If it just doesn't ever hold a vacuum then I would say a break somewhere (definitely check all the plastic lines as they go through the doors where they break from being flexed), although I'm sure you could also have an actuator that's bad both directions.

-Rog

If you here a wheezing sound from behind the steering wheel and your engine is slow to turn off you could have a leak or defective vacuum shut off valve located on the ignition switch (located right behind the steering wheel under the dash). To check this locate the two brown vacuum lines under the hood. One of these lines goes to the shut off valve located at the rear of the injection pump. The other brown line goes to the shut off valve located on the ignition switch. Disconnect the brown line going to the ignition switch and with the engine running apply vacuum to this line using your Mityvac. The engine should off immediately. If it does not, the next test is to apply vacuum to the brown line going to the shut off valve on the injection pump while the engine is running. If the engine shuts off immediately and you are able to hold a vacuum for a period of time (at least 15 minutes) then your IP shut off valve is OK, and the shut off valve on the ignition switch is suspect. This valve can be accessed by removing the instrument cluster and is easy to replace and cheap.

As you have realized most functions on the W123 diesel cars are controlled by vacuum and vacuum leaks can occur in many different places. Another common source for vacuum leaks is the vacuum reservoir at the tube leading into the reservoir. Test the reservoir with your Mityvac to see if it holds vacuum. It will take several pumps of your Mityvac to create a vacuum in the reservoir.

Another check is to check all of the underhood items controlled by vacuum. From the main vacuum line going to the brake booster from the vacuum pump there are two vacuum nipples. Remove the hose on the nipple closest to the front of the car and apply vacuum to the hose. Vacuum should hold for at least overnight. If not, you will need to isolate and check each underhood item individually (EGR valve, transmission modulator, etc.).

Some good shops use a smoke machine to detect leaks in the vacuum lines (pressurized smoke to pinpoint a leak) or they pressurize the vacuum likes with air and listen for the leak.

thanks BW. I don't belive my engine is slow to turn off - takes about 1/4-1/2 second it seems - after turning key. If I turn my car on and then IMMEDIATELY try to shut it off, it can take a few seconds to shut off. I've tested the brown lines with mityvac and i get immediate shut down. I should also check this ignition switch. Do I need to remove the steering wheel/dash? or can I access from underneath the dash through the removable panel? This wheezing is almost certainly a source of a leak.

So far I've methodically tested everything in the engine compartment, starting with the pump, brake booster, etc. I have reached the door system and I know there is a leak in it. I also know that my storage tank holds well. I'm going to continue going round the doors - as I'm performing lube/maintenance, and replacing a couple check straps anyway - i find it a worthwhile exercise.

I've read through all these responses -all very helpful but I'm still confused on what point - the check valve. I HAVE the yellow valve in the engine compartment, it's working - it goes from one into two ports. Is there supposed to be ANOTHER check valve between that one and the drivers door actuator?

EDIT - according to this http://www.peachparts.com/shopforum/attachments/diesel-discussion/75556d1261592167-w123-vacuum-interlock-diagram-w123vacdoorlockdiag_cghj564684.jpg it appears there IS a check valve after the firewall, in the dash - that goes to the drivers's door.

__________________
Andrew
Montclair, NJ
--------------
1982 300D Turbo
120k
Petrol Blue Green

It's been a while since I had my 83 300D (first MB ever), IIRC there may be another check valve attached to one of the yellow lines under the dash.

__________________
78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Okay, for sure that diagram is wrong on the red/green lines. The line going to the fuel door is red, which is lock. (If it only has one line it's the type that is held locked by vacuum and if vacuum goes away it unlocks automatically.) I've confirmed this since my earlier post.

What's insane is that I've never seen a complete vacuum diagram. I've seen bits and pieces (some apparently incorrect), but nothing showing the full system. Too bad I have so much removed on my car, I would totally make one.

-Rog

The check valve in the solid yellow line is in the door and should be attached to the yellow line (middle connection on the main actuator valve) just before the line connects to the main valve. I have had similiar problems on my 1983 and 1985 W123 cars and the valve is in the door. I have never seen a vacuum check valve under the dash. The valve is called the central check valve for door locks. It is part number 116-800-03-78 and is pictured in the Pelican Parts catalog on line - the new ones are black/blue color, my original one is gray/ white in color.

I can also confirm that the diagram I referenced earlier is incorrect about the red/green stripes on the vacuum lines. Other than that mistake it is a good diagram of the door lock system. There is also a good diagram of the vacuum operated climate control system.

You can access the shut down switch on the ignition switch by removing the lower panel but access is much better and easier by removing the instrument cluster. The cluster is a press fit into the dash. You do not need to remove the steering wheel. I have had good sucess by fahioning two hook wires from a wire coat hanger. Using about 8 inches of straight wire fashion a curved hook on the end of each wire. Insert a wire at each left and right end of the instrument cluster with the hooks towards the front of the car. Push the wires in as far as possible with the hooked ends facing towards the center of the IC. Using a pair of pliers pull on the straight end of the wires alternatively. Be careful not to pull on the plastic face of the IC as it will separate from the IC. The IC should pull out about 3-4 inches. At this point you will be able to reach behind the IC and unscrew the speedometer cable from the speedometer. Once the cable is released the IC will pull out another 3-4 inches and you will be able to remove the wires frim the back of the IC (mark them before removal). Using a 10mm wrench disconnect the oil pressure line from the back of the IC oil,pressure gauge. Pull out the large bundle of wires on the left side of the IC (no need to mark these wires as they only go back one way as a group of wires). Now the IC can be removed completely from the dash. DO NOT start the engine. If you do you will have oil spraying everywhere inside your car. This is the IC removal process recommended by Mercedes (they even make special hooked wires for this purpose but I made a set myself from a coat hanger years ago and they work fine - a friend gave me a set of the MBZ tools but I still use my coat hanger tools (I own 3 W123 cars , a coupe, wagon, and sedan).

The shut down switch is held on by two screws on the top of the ignition switch and has easy access. Hopefully the switch is OK and you have a disconnected or cracked vacuum tube.

Replacement of the IC is the reversal of the removal without using the hooked tools. If you have trouble reattaching the speedo cable to the back of the speedo, under the hood on the left side near where the back of the engine and front of the trans joins is a plastic holder thst holds the speedo cable. Disconnect the plastic holder from its metal bracket and that will provide additional slack in the cable allowing easier hook-up to the back of the speedometer.

Re-attach the plastic cable holder when finished.