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