The vacuum modulator is a vital component of automatic transmissions. It tells the transmission what kind of loadis being put on it, allowing the transmission to react withthe proper line pressures and shift points. Over time, modulators can develop leaks, suffer ruptured diaphragms, become bent, etc. Not only canthis cause annoying drivability issues, it can lead to premature transmissionfailure. TCI comes to the rescue with this line of adjustable modulators. Renew performance, and gain the ability to slightly raise/lower part throttle shift points and line pressures. Simply adjust the screw inside the vacuum nipplefor more or less diaphragm pre-load.