Hello everyone,
I am new on this forum and I was hoping that some of you can help me regarding a problem with a non shifting 1981 W123 300CD automatic transmission.

I got the car from my father not to long ago after he gave up halfway on restoring it.

The car was shifting and driving reasonably well (for a car with nearly 300k miles), but during the "restoration" at some point all the vacuum connectors under the hood have been removed and incorectly been put back together.
Now the car, thankfully, turns off but it does not shift into higher gears.

I tried several times to reconect the vacuum system but to no avail. I simply get lost in all the different diagrams for the different build years and models.
According to a diagram I found for a 81 non turbo the vacuum line for the transmission should go directly to the VCV but the line is simply too long and extends all the way to the 5way valve at the top of the engine head.
I was assured that the line from the transmission was not replaced.

All the other lines are color mismatched, and I am assuming it was like that since before the car has been bought by my dad.


I don't know if it is relevant, but the car is equiped with cruise control (I have been told that Cupes with a non turbo engine and cruise control are quite rare)


I was hoping that someone can send me pictures of their vacuum system correctly assembled for that model year.

Regards to all

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You have a transmission model 722.1 and I believe that on your model year the vacuum modulator does double duty that is: #1 Shift points and #2 Shift firmness. No bowden cable.

The VCV is supposed to simulate vacuum (the more throttle the lower the vacuum) so that it resembles a gas engine.

You can check the function/routing by simply connecting a vacuum gauge to the modulator line and observing what happens.

Look at page 3 of this diagram:

https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Engine/615/07-150.pdf

Hard to tell what I’m looking at in those photos. My 82 cd has a five-way splitter. Those five way rubber parts are not cheap as I recall. It looks to me like someone used some of those check valves to serve as splitters.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

In addition to the VCV the function of the check valve on top of the valvecover is that so when you close the throttle the checkvalve bypasses the vcv to give full vacuum to the modulator and minimize vacuum losses.


Also you cannot compare vacuum routing of an 82 cd to an 81 cd. Different transmissions (722.3 vs 722.1) and aspiration (turbo vs N/a)

Agree, but fundamentally the lines for ignition, locks, hvac, seatbacks, etc. are all the same so they need to be split out all the same.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)