Ok here goes. 1983 300d turbo federal. Automatic transmission doesn't know where the throttle is. Immediately goes through the gears on acceleration and no kickdown at speed. Can use the selector to pick my gear. Was positive that this was only affected by the Bowden cable. Cable pulls fine and returns to its rest position on its own accord. My only theory is that it has come loose from the lever inside the transmission. When I changed the cable on my 85 300cd I noticed that the cable has its own return spring which was separate from the return on the lever. I believe that on this transmission everything else (vacuum) controls shift firmness. Just looking for confirmation of my theory or contradiction and some new ideas. I assume that the lever in the transmission actuates a valve that modulates pressure. Has anyone seen this valve fail? Additional info, last trans fluid and filter change was 15,000 miles ago. Engine is running properly. We will see if I get any responses before I can't take it anymore and drop the pan.

 

Just dropped the pan. Cable is intact and actuating the lever that pushes the piston in. What now? For what it is worth, when manually actuating this piston it feels like only spring tension till about 3/4 of the way in and only then feels as if it is doing something else. What is this mechanism called?

 

Transmission shifts fine, albeit really early. Would this still indicate a spring problem? It was night and day. Leaving the neighborhood it worked fine, by the time I got to 470 it didn't downshift on the ramp.

Found one kit in U.S., in Florida. $91.07 and its on the way. By this time next week we shall see if the problem is solved. Thanks for the input ForcedInduction. One of these days we will have to get together. That 85 300cd that I converted to Federal turned out real nice. Was able to cut the upturn off the California airfilter housing and go straight to the turbo with flex pipe. Cut 5.5" out of the downpipe and rewelded. Like the looks better than my federal car.

 

Finally received and had time to install the kit in my valve body. No change in my transmission being controlled by the throttle. On the kickdown side the capsule was rattling so I did replace the spring in it as well as the small one below it. Replaced all other springs in the valve body with the "hard" shift setup as described in installation instructions. Performed all work on my steel welding table with no rags in site. Used MAF cleaner for all cleaning as it leaves no residue and is safe on plastics. Still shifts fine if I use the lever although this doesn't allow for first. Is it possible that I just need to dig deeper into the valve body? Dirt that I cannot see just pulling the side plates? Or wear that I cannot see? Issue with the governor overriding the shift valve before I reach speed? I am a capable mechanic but have little experience troubleshooting automatics.

Driving the ML 430 for the daily driver isn't helping my pocketbook.

 

I have exactly the same problem. Did you manage to sort it out?

 

You are right in thinking that the modulation valve plays a crucial role. If it is stuck or damaged, it could affect the transmission's behavior. Problems with this valve can result in unpredictable gear changes.

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