You’ve got questions. We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re looking at ways to fix a hard-shifting transmission.
J.W. Niagara Falls, NY
Q: I have discovered that the shifting characteristics of my TCI Turbo 350 Street Fighter transmission are not what I want for my daily driver. Specifically, downshifts at highway speeds (third to second gear) are much too harsh. Even after adjusting the TV cable, the transmission still shifts too hard.
The transmission is in a 1988 full size Chevy pickup, which has a 300-horsepower crate engine, stock torque converter, B&M oil cooler, and a 3.07 rear-end gear.
A: The TV cable cannot be run very loose or the transmission will not shift properly. Engine vacuum controls the downshifts through the modulator valve. Depending on the cam in your crate motor, your vacuum may be on the low side, causing the transmission to shift hard. Check to see if the hose going to the modulator is collapsed, or if it is connected to a ported vacuum source instead of manifold vacuum.