Modulator vs TPS

Some hydraulic transmissions use modulators to control the throttle valve. They mount to the transmission case and contain a spring and a pin that moves in proportion to engine manifold vacuum. These pins come in different lengths to adjust or modify shift feel. Adding a stronger spring or a longer or shorter pin will cause a firmer or softer shift. They have been replaced with throttle position sensors in electronically controlled transmissions.

Throttle Position Sensors are also often adjustable. Rotating the sensor left or right will change the signal sent to the TCM. The modulator is controlled by manifold vacuum and the TPS is controlled by throttle angle. Both sensors affect throttle pressure. Modulators are found on hydraulically controlled transmissions and throttle position sensors are found on modern electronically controlled transmissions.