I have a fully rebuilt c4 behind a 302 (warmed up. 300hp) two questions. #1 is the modulated pulling vacuum from the intake manifold or the carb? (my guess is manifold vacuum is needed) #2 when driving in a spirited fashion (tire smoke for days) the trans does not want to shift into second. I can hit the red line and the car will stay in first. I lessen the throttle and the car still won't shift for a full second or a second and a half. then it shifts into second normally. What is the issue? How should I address this? Any thoughts?
1. Yes the vacuum should be pulled from the intake 2. Did you have the transmission rebuilt with a shift kit? do you have the modulator hooked up? Have you tried adjusting the modulator?
first check and see if you have an adjustable modulator valve, there will be a screw in the vac stem.
Pull the vacuum hose off the modulator valve on the transmission, insert a small flat head screw driver in the nipple and adjust the valve. I don't remember which way to turn it, but that's how it's adjusted. If the screw driver doesn't work try an allen wrench, I think clockwise tightens up the shift points, counter loosens them.
I if may add some advice, if it's not too late. Don't exceed 3 revolutions on the modulator screw. According to B&M.
saw this post and thought someone may know, I have TWO vacuum lines going to my transmission. One is direct from the manifold as you mentioned and the other is connected to the distributor port through an engine coolant control valve. What is this second line for and does it have to be controlled by engine temperature? I would like to use this thermostatic valve instead for controlling my distributor port vacuum. Thanks for any input.
