64-71 Transmission Vacuum Modulator, C4/C6

Transmission Vacuum Modulator (64-71 C4 transmission 66-72 C6 transmission)

Adjusting the modulator:

Locate the vacuum modulator on the passenger's side of the vehicle. If you need to raise the vehicle, use the jack to raise the front of the vehicle and support it with jack stands on each side of the frame. The vacuum modulator is located just above the rear corner of the transmission pan--it is brass-colored, round, about two inches in diameter and has a small rubber hose attached to it.

Remove the hose from the modulator.

Insert the small flat-head screwdriver into the modulator, at the location where you removed the hose. Engage the adjustment screw. Turn the screw clockwise for harder, later shifts. Turn counterclockwise for softer, earlier shifts. Make adjustments one turn at a time, then test drive. Do not adjust more than four turns in either direction.