300SD transmission problems, help

Friend owns a 19?? 300SD. Runs fine although I always noticed the 1-2 shift was rather abrupt but not enough to jerk the car, and the 2-3 upshift happened
amost right after the 1-2 shift. Now the car does not shift into 3 or OD. Friend claims the transmission is filled up with the proper type of fluid and does not seem to be a linkage issue. I know that Ford transmissions use a vacuum modulator that if disconnected can cause hard shifts. Any ideas to try before the transmission gets rebuilt?
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Shift points are not a vacuum modulator issue. 1 - 2 shifts are harder than the others and a vacuum leak will cause hard shifts.
The transmission "knows" when to shift via a "pressure rod" (or cable) that runs from the throttle linkage on the top rear of the engine down to the right side of the transmission. Such early upshifts indicate that the rod's ball is disconnected from its pin, probably at the top of the engine.
The rod's length is adjustable. Pry the ball off the pin at the top of the engine. Gently pull the rod and allow it to return to its relaxed state. Then, without pulling or pushing the rod, try to reattach it to its pin. Its OK if that can be done without pulling or pushing the rod, otherwise adjust the ball's position (or the cable's mounting screw) so the ball fits onto its pin with the rod in its relaxed state.
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Hi,
I think you know about mercedes automatic transmission.. I have 124 300 D -85 and 4 th gear dont keep up, so you need to drive with 3 fist gears only.. sometimes when engine and gearbox is gold you can drive with D, but after a while it drops away.
I have right kind and right amount of gearbox oil. I have also changed oil filter from gearbox, but these didnt help.
Any ideas, hints, pictures, servise manuals etc?
Yours, naksi
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