I''m hoping someone can help me salvage my transmission (1984 300SD) with some wisdom on how to fix the problem I''m having: When I start the car in the morning, the transmission shifts fine. After the car has been driving a while, I begin to lose the ability to shift into the higher gears - first 4th, then 3rd, then 2nd, and as soon as I let up on the fuel pedal, the trans wants to abruptly shift into a lower gear. I''m thinking that perhaps there is a pressure issue, where pressure is building up over time with some relief outlet damaged or clogged. The factor other than time that changes while driving is heat, but I don''t know how that would cause this problem. The fluid level is right, the vacuum system seems to working OK, and the kick down solenoid seems to be working OK. Someone suggested it might be clogged governor screens, but I have no idea where they are nor how to get at them. Are there any manuals or books on these transmissions? Thanks for your help - Steven

Sounds like a valve body issue. Possibly the tv pressure control valve sticking.
Have you checked the kickdown switch, unplug it and see how it does.

disconnect the kickdown cable and see if that does anything.

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81 300SD daily driver/project
86 420SEL (sold)
85 380SE(in the graveyard)

Thanks for the reply, sounds like something to try. The next question is, how do I learn enough about this transmission to actually do this work? I have no problem working on the engine, but I have no understanding of automatic transmissions, and frankly the vacuum system looks like voodoo to me! - Steven