C-6 wont shift untill high RPM

My trans has been rebuilt buy a good trans man it shifts great  from 1st to 2nd but you have to turn about 4200 for it to shift into drive.once it shifts it shifts firm and im running about 55 if i back off the gas any it downshifts right back to 2nd. Trans does not have a kickdown hooked up.

capncruncher1965 wrote:My trans has been rebuilt buy a good trans man it shifts great  from 1st to 2nd but you have to turn about 4200 for it to shift into drive.once it shifts it shifts firm and im running about 55 if i back off the gas any it downshifts right back to 2nd. Trans does not have a kickdown hooked up.

Governor stuck, modulator valve bad or wrong one the modulator pin , or valve sticking . check vacuum going to the modulator valve. Kick down or throttle valve stuck in valve body.

Dont have a kick down hooked up think that is the problem? Im going to check the vacuum to the modulator tommaro.if it has  vacuum which modulator should i use. Thanks for your reply

Sounds like a vacuum issue . Either no vacuum . Make sure vacuum is full manifold vacuum.
Did see similar with a C4 that was hooked to ported vacuum

I wouldn’t waste my time Just take it back and make the guy fix it if you paid for a rebuild it should be right.

Replaced all the rubber hoze from carb to modulator it has vacuum for sure now will test drive tommaro to see if that fixed it

capncruncher1965 wrote:Replaced all the rubber hoze from carb to modulator it has vacuum for sure now will test drive tommaro to see if that fixed it

Must be FULL manifold vacuum from the intake , if it is on the carb ensure it is NOT ported

Put new vacuum hoses on it turned the screw in the modulator qutar of a turn out and bingo shifts perfect. Thanks guys for all your help and replys. Love this website