Hello all. I'm a newbie. Recently purchased a 1984 300CDT. It runs nicely, with a few exceptions in terms of occasional harsh shifting, which I seem to have solved for the most part by plugging up one of the arms of a 3-way rubber vacuum fitting that wasn't connected to anything. Still shifts abruptly on occasion and clunks when downshifting though. Other issues are the seatback locks don't work, the central locking system only works for a few minutes and no heat is coming from the lower vents into the footwells.
And hence, some questions - there are three lines coming through the firewall into the engine bay, which are cut and not connected to anything. One is blue (which if I've done my research right, is the seatback locks), one is green with a yellow stripe (which I believe is for the CCU) and one is black.
Are there any diagrams or photos to show where and how these three lines should be connected? I'm wondering if they are supposed to connect to the open arm I just blocked off.
Anyway, any help is much appreciated!

Vacuum diagrams for a 300CD? Sure:Definitive '83 Fed 300CD vacuum thread

Welcome to the forum.

Your research is correct - blue for seatback locks. Don't overlook the additional relay for the seat vacuum behind the glovebox. With the age of the car, it's likely the mechanisms in the seats themselves may be gunged up. A clean and lube may reduce the creaking noise accompanied by a functioning lock. You may also want to do this to free up the seat height tracks (side of seat handle) and the fore/aft tracks (front handle).

Green/yellow for A/C - nothing special about the coupe vs. a sedan. But leaks here will affect the seat locks. I could get my seats to lock if I selected Defrost due to a leak in the pod next to the gas pedal. Once locked, the seats held vacuum until the door opened (dumped via the relay behind the glove box). Fixed the pod and it fixed the seats.

Black might be the "cabin vent" and may not connect to anything.

Central locks only working for a few minutes could be the doors, the trunk, the fuel filler flap door, or the reservoir. Get a Mity-Vac and divide and conquer.

Tranny shifting and vacuum are related, but fixing the vacuum may not fix shifting. It would remove the question mark though.

How does the car shut down? Quickly, or does it run a few seconds after pulling the key? That's also vacuum. Brown lines to/from the ignition.

Thasnk very much! Will take a look at it all. Was definitely planning to remove the seats and clean up the tracks, etc.

Sorry, also meant to say that the engine does shut down very quickly when the key is turned off.

Well, I thought I'd post a few pictures which may give someone out there an idea of what I need to do. I have searched this forum and others, but have found no diagrams that seem to be specific to my car. Also bought the MB FSM CD, which doesn't seem to have any either.

One thing I did notice while looking at various photos and diagrams online is that I don't seem to have the little green vacuum dashpot. I haven't read anyhwere that my car should not have one, so I'm wondering if that may be contributing to the lack of consistently smooth shifting as well.

As you can see in the photos, the green/yellow line and the blue line are not connected to anything.

Any advice is greatly appreciated!

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The pics sort of help, but they're pretty small and too zoomed in to see everything. I really recommend you re-look at the link I posted above. It's got all the info for the '83 300CD and your car should be very similar.

If I'm seeing the pics correctly, it looks like someone either removed or re-routed the five way connector for most of the accessories and replaced it with a 3-way. That's why there's no room for the blue and green lines. If the blue and green aren't connected, you'll get exactly what you are getting: inop seat backs and no control of the A/C flaps.

You can see where there SHOULD be a 5-way (one-in, four-out) in the first pdf in the first post. A gray line comes in, two check valves go out(blue-seats and yellow-locks) a brown line goes out (shutdown) and a green line goes out (A/C).

In your first pic, it looks like there are two check-valves connected in series. This is wrong. They should be different outputs. Compare to the pic named "vacuum octopus" in post 3 in the link. Do you see the little blue collar on the checkvalve? That checkvalve is for the blue line on the seatbacks. Two sequential checkvalves wouldn't serve much purpose, it that's how yours are connected in pic 1.

If I'm seeing it correctly in the first pic, your brown line is connected directly to the main line instead of via a 5-way. This may explain why your shutdown is good, but other things aren't.

You should have the green damper/dashpot. In your pic 3 it looks like it's not there. You can see it clearly in the PDF named 617.95 Engine Fed and it's item #72. It looks like there's a four-way connector there instead of the damper off the three-way.

It also looks like someone has removed/messed with your EGR lines. In pic 3, there appears to be a white line and a black line that route from your valve cover block but they connect to the same vacuum line at two points. This is also incorrect. Look at the pic in post #2 "three Y's". You can see the black line goes to the bottom of the VCV and the white line goes to the top via the green damper. In your setup, they both appear to go to the top of the VCV, but it's hard to tell since it's small and partly obscured.

Advice: pan out, get a bigger view and try posting larger pics. If you have Office, try pasting the pics in a word doc, then saving as a pdf. The limits on uploading pdfs are larger so you can put bigger pics in the post.

1984 MB CD vac line routing underhood - YouTube

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83 SD

84 CD

It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...


I have the same car and post #8 in this thread cured my trans shifting problem

Toomany nice video!

thanks

You're welcome.

If you'd like anything further, let me know.

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83 SD

84 CD

Thanks everyone. Yak, I will relook at what you sent and also the video from toomany. Will see where it all takes me. Much appreciated!

Thank you all very much for the advice here.
Yak, the pictures, combined with toomany's video was very helpful in getting it all straight in my head. Probably won't have a chance to actually work on the car for a couple of weeks, but at least now I'll be able to sleep at night!
One question I do have in your "vacuum octopus" photo. One checkvalve is conencted to the yellow for the doorlocks and the other has the blue collar for the blue seatback line. What is the other side of that checkvalve connected to? Or is it just blocked off?

That's the five-way connector. Think of it like a pitch fork with the vacuum pump (gray line) as the handle and the source/source of the vacuum. The four prongs are "consumers". Each check valve is one "consumer".

The check valve with the blue collar on the rubber connector is in between the five-way/distributor and connects up to the blue vacuum line. It passes vacuum from the gray line to the blue line.

The check valve with two outputs is very similar: one hose in (off the five-way) and two yellows out (one to the locking system, one to the reservoir).

All of the lines in the octopus pic are basically the same lines in your pic #2 with the round grommet on your firewall.

If you're trying to make yours more like OE and can't find a five-way, you can substitute a 4 + 3 (one end of each will connect to each other) or 3 - 3-way (3 connect to two, the other two have 2 each open).

Okay, got it. I thought there was another "consumer" side to the checkvalve with the blue line on the output side. Really appreciate your guidance and patience. May have some more questions when I actually get started, but this has been a huge help. And, I was able to find a five-way on **************.com.

Is there a particular Mity Vac model that is the best one for working on the vacuum system? There seem to be a number of them.
Thanks very much.