I know that on the 1982+ cars, the function of the vacuum modulator is to smooth out the shift, and on the 1981 cars, the vacuum modulator is very important, as it can determine shift points, but on the earlier cars that have both a modulator and a rod, what jobs does the modulator have? The car in question, will not shift out of first gear. The transmission was rebuilt 2 years/20K miles ago, so I hope its not internal damage, but it may be.

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the rod controls the shift points. the modulator controls the "quality" of the shifts-- how soft/hard the shifts are.

if you can't shift out of first (or do you mean second? these start off in second gear) i'd check fluid level first, then check the kickdown switch under the pedal (disconnect it if it is stuck closed)

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1981 NA 300D 310k miles

If its not shifting out of first....it could very well be your kickdown switch behind the accelerator.....unplug the switch and see if the symptoms change...

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On a 1980 car there is a control unit that actually activates the kickdown solenoid when you come to a stop. Those transmissions would move off in 2nd gear, but the control unit makes the move off in first. I think it needs the vehicle speed signal from the cruse control system to work properly.

-J

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