Q: I recently replaced the 305 engine and TH-200 transmission in my G-Body Monte Carlo for a 350 with a mild cam and a TH-350 transmission.

My question is about the tranny. It was in a friend’s strip car, and had about 15 passes on it before I got it. The transmission has some kind of a hard-shifting shift kit and a small vacuum modulator.  I was told that the transmission will shift automatically, but that I should shift it manually at higher rpm because of the pump.

The problem is that I can’t reach those higher rpm in city driving without speeding. Am I doing any damage to the bands by shifting early? Could I adjust the shift points with a different modulator? Will that allow me to let the transmission shift automatically at lower speeds?

a light blue monte carlo ss from the mid-1980s modified in a pro street custom style
(Image/OnAllCylinders)

A: You won’t damage the bands by shifting early. However, you aren’t helping keep transmission fluid temperature down or fluid pressure consistent, either.

You can add an adjustable vacuum modulator, but this is limited as far as changing shift points. We suggest asking your friend whether the transmission’s governor was modified for his race car. If it was, you might have to modify it again to suit your street driving. Depending on what rear axle gear ratio you are running, you might want to go to a higher ratio to compensate for the transmission’s shifting characteristics.

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