This is not a situation anyone wishes to find oneself in, after buying a car.

Had the car been sitting for an extended period, before you purchased it? If so, do you know how long?

What does the transmission fluid look like?

My 300td wagon had pretty much the same issue when I installed a .117 transmission that I had had sitting in storage for 4-5 years. After much messing around (by me), a trans shop was able to pull the tail cone and access the governor and free it up. I am driving the car now.

If you are able to find a .120, what you propose to do is of course the high road in terms of getting things back to spec, but you may have some trouble finding one as (as far as I am aware) it was only used three model years, the production lifespan of the w116 SD.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

Ironically enough, the original selling point for me; at least one of them, was that the transmission was replaced about a month before I bought the car. One thing I noticed that the car always felt like I was driving slow, here is what I mean: I'd look at the speedometer and it would say 35mph felt like I was going 25mph. Then one day on the highway it died, came back to life and then just died completely.

Tranmission fluid is a beautiful red color, partly because I have poured 2 quarts of new trans-fluid in.

I have a 722.120 sourced, I am also looking for ones closer to home as well.

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Nosce Te Ipsum "Know thyself"

If you'll let us know where you are, more folks may be able to help.

Fair point

Chicago land in Illinois

__________________
Nosce Te Ipsum "Know thyself"

I'm probably in the wrong place for a post, but I also have a problem with a 722.120.
It started with just prior to a fluid/filter change, flair on 2-3 shift and apparent neutral upon right hand turns.
After the fluid/filter change, the transmission will only stay in 2nd. No flair or slipping or attempt to shift, even when run up to governing max rpm of engine.
Sometimes, not every time when letting off accelerator it will go to "neutral" and will not re-engage until a full stop.
Items already checked are, Vacuum - good at 28inHg , Modulator rod adjustment, Vac Modulator - no change with any adjustment.
I'm thinking the Centrifugal Governor may be to blame here but I do need help with this as I'm overwhelmed with "Murphy's antics (broken timing belt on volvo diesel resulting in many valves that have to be cut out of the cylinder head)
Also, Does anyone has a hydraulic schematic for these 722.1xx transmissions, it would be of great help to me to see one.