'83 240D automatic 219k miles

Going through my vacuum system (hoses, ck valves, etc.). A few questions:
What is the purpose/function of the green "dashpot" (as I've seen it called) that comes off of the VCV?
Is it a restrictor, as opposed to a check valve?
Should it pass air in either direction?
Do they "wear out" and is there a way to determine that it's not functioning properly?
And, lastly, can it be installed in either direction?

Thanks, in advance.

I don't think it is a check-valve. The only check-valves I know of are the one on the main vacuum tube (a tiny nipple on either side to supply components) and the yellow one on the source to the door-lock system (that circuit has a large reservoir in the trunk top also).

I don't think it is a purposeful restrictor either since those are the little in-line couplers which are same OD as the vacuum hoses. I think it is a small reservoir to give "capacitance", working with a restrictor to form a "first-order delay" like an R-C circuit in electronics (ref. any Physics text).

I recall it is in the path from VCV output to transmission "vacuum modulator". In 1985+ cars, there is a "vacuum amplifier" (blue saucer) in-between (perhaps a good mod for earlier cars, I added on my 1984). If true, why one needs such a delay is another question. The purpose of the VCV is to simulate the intake manifold vacuum of a gasoline engine since the transmission is designed to shift based upon that signal, since originally designed for gasoline cars. The VCV works solely upon the accel-pedal input to the injection pump. Perhaps a time delay is needed to simulate lags in intake vacuum to throttle changes in a gas engine. Your transmission might stay in gear longer when you floor it (higher rev's before shifting) if you remove the green chamber, which might be better for drag-racing (good luck with your diesel at the track).

There is also the Bowden cable to the transmission off the accel pedal linkage. I suspect that is like the "kickdown linkage" in my old Mopar gas cars. Chrysler transmissions don't sense intake vacuum, but rather have an internal speed sensor (spinning hydraulic valve in older transmission, e-sensor in later ones). I think old Ford transmissions did use intake vacuum, since have a large vacuum diaphragm on the side like our M-B transmissions (B2 piston is one). GM might have been more like Chrysler. Obviously, I am not the expert. I did teardown the transmission from a salvage 1983 300D, but just to save the hard parts for the future (case was cracked). Gave little insight to how it works.

There is a long discussion of how to adjust the transmissions in our cars you can find in a google. I filed away for when I ever try that, which I might since my 1984 makes the first shift a bit late (to 2nd gear? but some say they start out in 2nd gear), though the little kick isn't bothersome enough to move tweaking it to the top of my list.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Thanks very much for that excellent response. It's quite helpful and sheds light on a fairly mysterious aspect of these cars.
My '83 240D doesn't have the "Bowden cable".
My car does seem to delay shifts on acceleration or shift too soon at low RPM's. Never had another W123 (or Mercedes, for that matter) or drove a "nice" one, so nothing to compare shift behavior to. Might all be "normal" for all know, but I suspect the transmissions was a little more well behaved, when new.
Also seems to shift a little hard. Not bang, but not smooth, either.
I know the VCV's are now "un-obtainium" and didn't really know where else to look. I ordered a new "dashpot" because they're cheap and available and mine seems to pass air (blow test) very easily in both directions. It very well may be the original. All the vac lines/connections seem to be in order.

It's a mini reservoir to ensure smooth vacuum signals .

Before you change, adjust or delete anything, fix all the vacuum leaks 100 % ! .

Then, pull the vacuum hose off the VCV and test drive the car, after it's been driven long enough to fully warm up .

If it up shifts okay with the hose disconnected you're almost done .

If it still shifts too soon, too late or stacks the 2/3 shift you're going to need to make adjustments, this isn't difficult but first you MUST change all the ATF including the torque converter there's a 5MM Allen plug to make it easy) and replace the tranny's filter .

Then you can move on to adjusting the tranny's internal pressures with the tranny fully warmed up then lastly if necessary you can adjust the VCV, this too is simple .

If you do the steps out of proper order you can expect to make it far worse and never get it right again .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Thanks for the very informative response. Before posting the question, I had just changed the ATF and filter. Also drained the torque converter. Done while fluid was "hot". The old fluid wasn't "terrible" (not burned in smell or appearance, still red but darker than new), nothing in the pan. The change made a noticeable, albeit subtle, difference. Absolutely "felt" better...no change in shifts.
I will follow your suggestions and report back.
The car is " all 4 wheels in the air" at the moment....exhaust work (done yesterday), idler arm bushing r/r, one upper and one lower ball joint.
Due to my current work schedule, may be a few days before I get her back down.
Thanks again!

Well, finally got the front end back together...2 new lower ball joints, new shocks, new springs, 1 new upper control arm and bushings, idler arm bushings and a steering damper. All I can say is "WOW!!" The car has been transformed and that's an understatement. I literally cannot believe how much better it handles. And, boy, does it ever feel tight! Handles the "twisties" with ease and bumps/road imperfections are, now, of no concern. Firm and quiet over the road. Truly a joy to drive. Am I ever amazed. Never thought this car could handle so well.
I mentioned, in my original post, of having some shifting issues. I changed the "dashpot" and much to my surprise, delight and amazement, all my shifting problems vanished! Never thought that one little green plastic part could have such a profound effect? But, believe me, it's like a different car/transmission.
All I can say is don't overlook the dashpot! Like all the "old timers" tried to teach me growing up, always change the simple things first. Don't go looking to open a can of worms before addressing the easy things (like checking the integrity of all the vacuum connections/tubing).
Thanks "Nate" and "BillGrissom" for sharing your knowledge and advice!
Guess we can "close" this one.

Always nice to hear things worked out well .

Folks are always amazed at how quickly I can move my W123's through the twisty bits ~ I sometimes overtake sports cars .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Thanks Nate. Always appreciate and look forward to your input and generous sharing of your wealth of knowledge.
One thing I forgot to mention regarding the front end rebuild: I had to purchase, and change, the coil springs twice. This was the result of, IMHO and experience, buying an inferior brand. The first brand I tried was from "Lesjofors". In my haste, inexperience and quest for the lowest cost (never a good motivator), I confused "Lesjofor" with the brand "Lemforder", which I've always heard good things about on the forum.
Sorry to say, the "Lesjofors" were sorely lacking and not up to the task by a long shot. After the installation, it looked like I had installed a "lowering kit" on the front end of my W123! I cannot recommend this brand of coil spring! "Caveat Emptor", big time!
Unfortunately, I was past my retailer's "return date", as I try to purchase needed parts well in advance of using them. Reaching out to "Lesjofors" was an "exercise in futility".
My second set were "Bilstein" and they worked like a charm. The car is level with the correct "ride height" and handles like a dream. Highly recommend this brand.
As "they" say, "experience is the best teacher".
BTW, if anyone is interested in the "Lesjofors", and I can't imagine why they would be, you're welcome to them for only the cost of shipping. They were on my car for only a couple months and not many miles.
Apparently, they'd be great in a W123 without an engine...lol /s