Vacuum Leaks 300D TurboDiesel W123

[DougS]

_____
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 <con
underline trx at shaw dot ca>
Regards / John

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.

[Seum]

Post by DougS

_____
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 <con
underline trx at shaw dot ca>
Regards / John

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.

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 :-)

[j***@nowhere.ca]

Post by DougS

_____
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 <con
underline trx at shaw dot ca>
Regards / John

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.

_____
Doug,

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

Post by DougS
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?

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

Post by DougS
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.

_____
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 <con underline trx at shaw dot ca>


--

[Tiger]

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

[j***@nowhere.ca]

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

_____
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

--

[Tiger]

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.

[Tiger]

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

http://boostnbenz.1baddsm.com/DIY/Vacuum/

[j***@nowhere.ca]

Post by Tiger
I just did a quick Google search... vacuum schematic found in 30 seconds.
http://boostnbenz.1baddsm.com/DIY/Vacuum/

_____
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

--

[Tiger]

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

[DougS]

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

One spot worth checking for all vacuum leak problems is where the
vacuum lines pass through the firewall going
from the engine compartment to under the dashboard.
Last two problems I had, the plastic lines were cracked
right where they pass through the rubber grommet.
While checking and trying to move one of the suspect
lines it broke right off in my hand.

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).

[Jens]

Post by DougS

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

One spot worth checking for all vacuum leak problems is where the
vacuum lines pass through the firewall going
from the engine compartment to under the dashboard.
Last two problems I had, the plastic lines were cracked
right where they pass through the rubber grommet.
While checking and trying to move one of the suspect
lines it broke right off in my hand.

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).

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.

[j***@nowhere.ca]

Post by DougS

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

One spot worth checking for all vacuum leak problems is where the
vacuum lines pass through the firewall going
from the engine compartment to under the dashboard.
Last two problems I had, the plastic lines were cracked
right where they pass through the rubber grommet.
While checking and trying to move one of the suspect
lines it broke right off in my hand.

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).

_____
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

--

[j***@nowhere.ca]

Post by j***@nowhere.ca
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. I also finally located my W123 service manual on CD. 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.

_____
Jens/Doug/Tiger,

Here is a link to the section on central locking system from my W123
CD:
http://dl.dropbox.com/u/25612291/W123_Central_Locking_System.zip

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

--