There are, in fact, four different valves in the valve body that are involved in the control of the basic/working pressure. It very well may be that one or more of them is stuck or that a spring is broken. And yes, your symptoms can arise from that.
Much easier to remove and inspect the valve body than the whole box.

Thanks Frank, I'll have to do just that. Looking at my valve body diagram, I see what you mean. 4 different valves that appear to be related to working or basic pressure. I'll remove the VB soon and dig in. Would be a shame to replace whole transmission because of a broken spring.

Folks, very interesting development!
I pulled the valve body, split it, and found a potential issue with the "Basic Pressure Control Valve".

Here's a photo of the valve after I removed the spring:
https://ibb.co/PtwBjSc

Here's the location on a diagram:
https://ibb.co/B263VfZ

Ok stupid question... this thing is supposed to move right?! I assumed so, because it's a valve, but it's not moving AT ALL. I have gently pushed the "rim" visible in my first photo, as well as further inside and I cannot get any movement whatsoever.

Assuming I haven't thought of anything, is this my smoking gun? If this was jammed in such a way that it was venting working pressure, that would certainly do it..

I just want to make sure I'm thinking of everything here. If it is indeed stuck, I'm not sure how I would get it unstuck without marring anything.

TIA!

Yes, the valve is supposed to move. Does the bore (or a portion of the center of the bore) extend through the valve body to align with the 1-2 command valve? if so, it may be possible to tap the pressure control valve out from that point.

Thank you Frank, I actually did get it out. Your idea was a good one, but the end of the bore was a dead end. So, I had to use a screwdriver with perpendicular force. With some solvant and a little persuasion, it's out.
It's definitely sticky, not butter-smooth like the other valves. Unfortunately I marred the valve itself getting it out. The bore looks good (phew).

If anyone reading this has a parts valve body, and could sell me this valve, I would be grateful. Otherwise I can have to make a trip to the yard, but it's a little time consuming.

Here's my proposed plan:
-Hone the bore, replace the valve.

-Clean the rest of the valves and bores. The inside of the valve body (the "maze") is actually pretty clean. There's a little bit of clutch material, but it looks like it's flowing fine.

-Reinstall with fresh fluid and filter + some trans-x to help the cleaning process.

If the issue is fixed, great. If not, I won't have spent too much time or money on it.

Anything I'm missing?

Can you post a pic of the valve, and the marred area? It may be possible to dress out scrapes on the valve, and reassemble it with the scrapes away from the port(s) that the valve passes. There is always some leakage past the valves; a scrape simply increases the leak. The process of dressing scrapes is to insure that there are no burrs that could cause further sticking.

Thank you Frank, I am gratful for your knowlege. Here is a photo of the valve:
https://ibb.co/YXTJ4gY

It may look like light glare, but if you look near the top of the valve (toward the 10 o clock postion) you will see a scratch going the same direction that the valve slides.
I assumed the valve needed to be as tight as possible for leakage, so, if leakage is ok, I do belive I could smooth this out.

There are other nics too, but they are in the are where only fluid travels and shouldn't be an issue.

That scratch should be OK; the objective of dressing/stoning is to insure that there is no burr that is greater than the OD surface of the valve.

Brave guy imgolden, getting into a trans !!

Good luck.

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

I don't know if someone mentioned this but there is a port on the transmission to check the pressure and there is a fitting you can buy to connect a gauge.

__________________
84 300D, 82 Volvo 244Gl Diesel

Hello all,

I wanted to update this thread for the common knowlege. I also have a new issue unfortuntely..

I ended up taking the valve body apart in my old transmission, cleaned it very well, found a few sticky valves, put it back together and.... no change.
Total pressure still very low, I'm assuming the pump had failed but cannot confirm.

I then decided to replace the transmission, and do it right with a rebuilt unit from Sun Valley. A friend of mine graciously offered his help and use of his lift. Took us 2 hours to get the old unit out, and 3 hours to get the new rebuilt unit in. "While I was in there" I did the flex discs, and the rear centering bushing on the drivshaft that was damaged.

So now today: Took it for a long drive and got the fluid level dialed in to perfection. It shifts well, but now I have one new issue:

At 55mph+ I feel a subtle pulsing vibration, about twice per second. It's more pronounced the more throttle I give it. It's pretty mild, I doubt my wife will notice it, but it bothers me for sure.

Perhaps I did something wrong with the driveshaft? I marked the halves and put them back together properly. I also torqued everything down to proper spec. Any ideas what would cause this vibration?

TIA!

Thanks for this very useful post and digging-in. I stripped the innards of a 1983 300D transmission and stored them for the future (case was cracked). Didn't look closely at parts, but seemed a little easier inside than some photos suggest, though not as simple as the Chrysler hydraulic transmissions I've rebuilt.

Many things can cause a vibration and perhaps you are just attuned to feel for things after your tranny swap. I once had a similar vibration in my 1969 Dodge Dart slant-six on a road trip. I would feel it begin ~55 mph then decrease a bit at 60 mph. Drove home 350 miles with no issues. Found the rear U-joint in the driveshaft was totally rusted out, loose and with some needle bearings missing. A fairly easy replacement even for me as a gomer 30 yr old with just a hammer, punch, and sockets for backup.

Of course, your car has rubber flex-plates instead of metal U-joints and a 2-part driveshaft with center bearing (if like 82-85 300D). The center bearing is supported in a rubber bushing (read, haven't been-in there) so can wobble if the rubber falls apart. Perhaps in your parts replacement, you cracked that rubber if old. Sounds like you did, and your car has a bushing instead of a bearing. Anyway, I'd check all that before fingering the rebuilt transmission. If your's has IRS, there are likely rubber sub-frame mounts which can degrade and let the rear jiggle around, but likely a much lower natural frequeny than 2 cycles/sec which is more a driveshaft natural frequency.

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

Thanks Bill, I certainly feel like a Gomer sometimes at 32. I only really picked up a wrench in my late 20s so I am still learning a lot.

I just happened to replace the carrier bearing on my other w123, because it was shot. The symptoms were certainly different than what I’m experiencing on this car. Further, when I had the driveshaft out I inspected the bearing closely and it looked very good. Mercedes part too, so I didn’t want to replace it.

I don’t think the transmission is the cause, because those guys are seasoned professionals and they tested the transmission before shipping to me.

I am thinking driveshaft. One question: if one of the flex discs isn’t completely seated into the yoke of the transmission, would that cause vibration? I recall seeing that one of my new discs didn’t seat completely flush, there was a slight gap. I didn’t think anything of it, because that gap is front/back and I didn’t think it would cause a driveshaft imbalance.

Bill, you said that 2 cycles per second is typical driveshaft frequency, how can that be? It’s certainly spinning much faster than that. Just curious what makes you say that.

Thanks!