W115 vacuum madness: two vacuum tanks, no check valves, lots of questions...
 

Just bought a 76' 240D a month ago, and I'm beginning work on the vacuum lines. Now I won't trouble you all with requests for a vacuum system diagram as every single other person has asked for in the past, apparently they aren't out there for the w115 chassis. There are some diagrams on this Peter Schmidt Transmission site, but not for 76' 240D that I can see. If any experts out there know which one there is similar, I'd love to know.

I wanted to overhaul the whole damn system, so I started with the source - the vacuum pump. The pump holds 22"Hg of pressure while the engine is running, so everything looks good there.

Now I know there are supposed to be two blue check valves in the vacuum tubing in the engine bay to keep pressure in the system when the engine shuts off, mine however are missing. Someone has been doing some funny business with this car... Below you'll see in the first image (pic 1), they're nowhere to be seen. The OEM check valves list on peachparts for $26, third party by Vaico for $3, is it worth it to go OEM with these little check valves?

I've also diagrammed out the tubing so it's easier to follow (pic 2). Which leads me to my next question...

I've only read about there being one reservoir in the front left fender (drivers perspective), however I have two reservoirs (see pic 3). Is that standard? Or some more funny business by the previous owner?

Also, what do the two tubes that run into the firewall go to? One is green with a yellow stripe, and the other is black (see pic 4).

I've already removed all the door panels to check the door lock actuators, all three of them need replacement gaskets. In the meantime I've plugged the door actuator vacuum lines with golf tees. I've also tested the actuators in the trunk, both are holding pressure. So from my understanding, I should have pressure within all the lines related to door locks.

Using a hand pump, I've tried applying pressure to the black line and the green line that runs from the engine bay into the firewall (pic 2 and 4). The green line holds no pressure at all. The black line shoots up to 15"Hg after 1-2 pumps, but falls back down to 0"Hg within a second. Also, when the gauge hits around 15"Hg (black line) there is an audible tone heard from something inside the car. You can listen to it here. Could just be some tiny leak making the sound as pressure escapes, but I figured I'd mention it.

So, what is sitting between the door lock vacuum lines and those green and black lines running into the firewall? Will I need to remove the dash and other panels inside the car?

thanks for reading through my vacuum epic!

This should answer most of your questions.

Alright, that diagram confirms it - there should only be one reservoir. Wonder why someone though another would be necessary since they both hold pressure....

Left Coast: I emailed you about getting a full size of that image, I think the forum software shrunk it down :mad:

Got your email and replied.

The diagram does show a second supply tank for the AC. I don't have a W115, so I can't tell you where it should be located, but clearly the car had two reservoirs if it was factory equipped with AC.

the fire wall lines , most likely are related to vacuum flaps for defrost ect, esp if it had AC , there is also a switchover valve. The whole system works as a unit for the most part
I have a lot of various lines, and filters from my resurrection of 2 W115's so if you get stuck for original parts let me know