Hi,

A while back I posted about a problem with my VCV valve not working properly. Well, I have since found some vacuum leaks. Using my hand pump, I have found no vacuum being held in both the blue line and the yellow with red stripe line under the passenger carpet. I started in the back of the car and both the trunk lock as well as the fuel door lock are holding vacuum as are the lines. When I get up into the cabin though, there is absolutely no vacuum being held. I'm guessing that this is related to the master door lock. Can anyone confirm this? Also, is there only one master vacuum switch and is it located in the driver's side door only?

A confusing issue I'm having is this: the vacuum diagram sticker on my car's frame does not match the way the lines are set up. On the diagram, there is a 5-way connector attached to the gray line that comes off the brake booster main vacuum line. My car has a 6-way connector attached to this line! The diagram does not show all of the lines so I'm wondering if someone has a better diagram? My car is a 1984 300CD California model.

I want to completely overhaul the vacuum system so this car functions like it was intended but the diagram I have to work off of is not complete enough. Thanks!

I had the same issue.
Changed the door lock master element and some of the door lock pods. didn't help.

before you change anything, I would recommend isolating the lines that run from the engine compartment into the firewall. Check to make sure you have proper vacuum from the pump.

the lines running through the firewall, on my car anyway, were for the dash vents, the door locks, and the seats (couples only I believe).

my leak turned out to be the lines running under the dash. I have read that the vent pods are tricky to replace, and are usually bad due to age and heat, etc.

I wound up just plugging the dash vacuum. everything else seems ok.

I will look for the diagram that I used. plucked from one of the fora

I'd suggest you start back at the "Front" of the vacuum system where it enters the car, testing each of the main feed lines that enter the vehicle to figure out which branch(es) of it are or are not leaking. That's the first step before trying to find specific devices that may have a leak. It lets you rule out large portions of the system at once.

Here is a guide I wrote up quite a while back on the technique for making your way from front to back of the car when diagnosing your vacuum door locks.

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

The system on your car will be similar if not identical, so it's worth a review. Beyond that, you can apply the same diagnostic steps for the other systems that are inside the car - namely the climate control (usually a green line with a yellow stripe), ignition switch/fuel shutoff (brown lines), and in the case of the coupes another line that feeds the seat back locks.

Going back to what you've found so far, the blue line that is not holding vacuum is for the seat back locks. This branch of the system locks the seat backs when the engine is running as a safety feature.

And as noted in the door lock diagnosis guide I linked above, the yellow with red stripe line is for the lock side of the door locks.

Hope this info helps you down the right path.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

My 84 & 85SDs don't lock automatically as a safety feature. They are vacuum controlled and can be controlled at the doors. Do start with each line from the front back. Just find a joint and pull a vacuum. Move further down line isolating vacuum loads until you find & plug the leaks.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Maybe this will help you



http://www.peachparts.com/shopforum/diesel-discussion/160169-w123-vacuum-interlock-diagram.html

Or maybe this Google search

https://www.google.com/search?q=mercedes+vacuum+lock+diagram&biw=1067&bih=712&source=lnms&tbm=isch&sa=X&ved=0CAYQ_AUoAWoVChMIj_mc6Oy4xwIVBX0aCh2O0AV5&dpr=1.2



Charlie


sent from my pos computer

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

So I checked all of the users of the vacuum individually and didn't find any leaks besides what I already mentioned, I guess that the light blue line goes to the seat back locks for my coupe which not surprisingly don't work. I plugged all vacuum lines except for the line going to the VCV and the modulator and went for a drive. Still jerking poor shifting transmission. Once I got back I checked and found that the modulator line was leaking vacuum quite a lot. When the weather gets nicer I'm going to attempt to replace the modulator assuming that the line itself isn't leaking which I haven't confirmed as of yet. I have a new modulator with the upgraded plunger, hopefully this will be the fix for my horrible shifting car.

Sounds like you're on to something.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!