What does the vacuum modulator do?
The vacuum modulator is a canister that contains a diaphragm and a calibrated spring. The diaphragm senses changes in engine vacuum due to throttle position/load changes and transfers the diaphragm motion to the modulator valve in the transmission. The calibrated spring opposes the diaphragm movement. This provides the means for the transmission to adjust internal pressures based upon torque demand by the engine.