I swapped an auto transmission(non turbo) from a 1987 300ZX into My 1989 300ZX. The car shifts fine, but the motor revs to almost 3500 RPM's before shifting under normal acceleration in all gears. After researching online, this appears to be an issue with the vacuum modulator. Are there any adjustments that can be made to this part? If not, what else could be causing the high RPM before shifting?

Thanks

 

There is nothing to adjust with the vacuum modulator, but they can go bad causing erratic shifting. Pull the vacuum line off the modulator. If ATF drips out, the modulator is bad. Be careful not to lose the little plunger pin that can come out with the modulator when it is unscrewed. I would check and make sure the pin is installed before screwing the new modulator onto the transmission. Use a small pair of needle nose pliers to remove the pin. ATF will run out the hole. If you haven't changed fluid in the tranny, now is a good opportunity to do so.

This tranny also has an electronic overdrive that only operates once the tranny has reached an acceptable operating temp. If you jump in a cold car and go roaring off down the highway, it can take 10 minutes (usually 3 to 5 for my car at 60 to 70 F) before the overdrive decides to kick in. Until that happens, it will feel like the last shift is taking forever to happen. Make sure the button on the shifter isn't set to keep the overdrive locked out.