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Vacuum Leaks 300D TurboDiesel W123

_____ Hello All,

My 300D W123 (1985) has developed an annoying vacuum leak that prevents the central locking system from working properly. The vacuum pump is fine, pulling 20" Hg. The circuit that appears to be leaking the most is the locking/interlocking line (my guess) to the RHS doors. These circuits are "fed" via a vacumm reducer that drops the vacuum from 20" to about 15". The reducer has two "outlets". One outlet goes to a yellow/grey_striped line, while the other outlet goes to another yellow/???_striped line (i cannot see the colour of the stripe from the engine compartment). This is the line that leaks a lot. I only get about 5" of vacuum when that line is connected. It causes failure of the engine shutdown actuator. So, for now i have disconnected the locking/interlocking lines, and plugged the outlet in the tee to maintain vacuum in the engine shutdown circuit. All three door plungers are in the locked position so that we can use the car.

Does anyone have the trouble shooting guide for the vacuum system of this car, and a a full schematic of all the lines, and vacuum tanks. It would be of great help to locate the trouble spot, and make a repair. At the moment i have the RHS front door cover removed. I had to repair the inside door handle, and tighten a few bolts, plus inpect and replace the plastic foil.

If you have schematics and want to send them to me, please use

Regards / John

Reply to
<jch
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It is quite possible that the problem is the valve in the drivers door that gets actuated when you lock and unlock the doors. This is a plastic valve and is very prone to failure after this long. I have a

1984 model of the same car. I also have the same problem, but mine is a slow leak only when the doors are locked. It could also be the yellow check valve (two way valve in the engine compartment) that is leaking have you checked to make sure it holds a vacuum correctly?

I may have the schematics for the vacuum system, but I'll have to look for them later. If I find them I'll send them on to you.

Reply to
DougS

I bought my MBZ 240D W123 in 1984. I DELIBERATELY, from previous experience, decided : No electric doors, no electric seats, no electric sun roof, no central vacuum lock system, etc. etc. It is now 27 years old and, apart from one problem with wiring, I fixed the very few things that needed repairs or replacements. 3 cheers for simplicity :-)

Reply to
Seum

_____ Doug,

I will check the leak with the "control knob" in the driver's door when up and down to see what gives.

_____ The yellow valve is ok, and is currently sitting on my workbench.

_____ Please do, it would help tremendously. I found that the pneumatuc "motor" the right front door has a bit if a leak around the stem that pushes/pulls the mechanism and the locking knob. I plan to pull the "motor" out of the door to see what vacuum i get at the control lines.

/ John

Reply to
<jch

Don?t' forget the vacuum canister.... some older MB has them and they do go bad too.

Reply to
Tiger

_____ Tiger,

Understood. Where is it on my 1985 300D turbo diesel? That is why i am looking for a diagram, and component locations.

I know where this vacuum cnister is on my 300SD; under one of the "false" plastic fender covers at the front

/ John

Reply to
<jch

If I recalled correctly, it might be under the rear deck in trunk. I do know on the W126 later model is located in driver wheel well behind black plastic cover. On some MB, it can be in the engine compartment too.

I personally have not seen any one of them.

Reply to
Tiger

I just did a quick Google search... vacuum schematic found in 30 seconds.

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Reply to
Tiger

Tiger,

Try following some of the links. They do NOT produce the content i expect judging from the link title. Will do some searching myself to see if i can locate the originator of this website.

/ John

Reply to
<jch

My apology... I didn't realize someone would want to make money from helpless W123 owners... that is so specific target group... strange.

Reply to
Tiger

I think that website that it pointed to was just abandoned. It was linking several folders deep, and the website is now for sale. It might be possible to copy the link location and go look it up at archive.org (the internet archive).

It seems like the OP looked for leaks there, but maybe not. As for the vacuum storage, the '85 W123 should have it in the trunk on the right (passenger) side above the fuel tank.

I'm interested in this topic as well, since I have similar issues with my '84 300D. Mine only loses vacuum when the doors are locked though. So, I have less looking to do (hopefully).

Reply to
DougS

A check valve between the pump and the entire locking circuit makes sure that once charged ("vacuumized") the vacuum should remain stay the circuit. A "tank" located in the trunk coompartment serves as reservoir, so pump does not need to supply everyting at the same time.

Same thing goes for the A/C control circuit if equipped, i.e. it has check valve and tank.

I'm not sure which one, but one of the circuits (tanks) also provides vacuum to engine functions.

Heavy leak in any of the two circuits will of course prevent the pump from charging any of the circuits. This is the first point to isolate the problem to one or the other circuit, simply by taking of the line to the check valve and blocking it.

Inside the locking circuit a switch will supply vaccum to either the closing or opening function of the lock actuators. The outputs of the switch is distributed to all actuators.

If the leak is only seen when locking or unlocking, the leak should be searched for in that respective distribution circuit. If the leak is also present when not locking/unlocking, the problem should be searched for in the supply circuit before the switch. Here the tank is a very likely suspect (it is in fact the only thing connected except for the switch).

I cannot match that logic with your findings. Except you say one line is leading to the engine compartment. That could be for engine control, and if this is the case, you could search in that direction.

Reply to
Jens

_____ Doug,

I am making progress. Found a leaking vacuum servo in RHS front door. Have applied silicone sealant to see if the will do the trick. New vacuum serve here in Canada is $91+tax. Vacuum tank is very good, no leaks. Also located my W123 service manual. It has the full test and repair procedure plus all the diagrams. Will post a link to my DropBox folder for you to fetch it.

/ John

Reply to
<jch

_____ Jens/Doug/Tiger,

Here is a link to the section on central locking system from my W123 CD:

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Table of Contents

80 - Central locking system, comfort hydraulics

010 General

020 Design and operation of central interlock 200 Removal and installation, as well as adjustment of vacuum switch of driver's door 210 Removal and installation of vacuum element of front passenger's door 220 Removal and installation of vacuum element for rear doors 230 Removal and installation of vacuum element of tank filler neck flap 240 Removal and installation of vacuum element for trunk lid 241 Removal and installation of vacuum element for rear door 250 Removal and installation of vacuum supply tank 260 Checking central interlock 900 Functional diagram central interlock 901 Functional diagram central interlock and air conditioning system 902 Functional diagram central and seat backrest locking system with air conditioning system

The zip file is about 4.7 Mb, and should download quickly. It has a collection of PDF files.

I cannot tell if the file has been downloaded by anyone, so i will leave it "in the cloud" on DropBox for about one week.

/ John

Reply to
<jch

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