Modulators and Load Sensors
Some hydraulic automatic 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 the engine's manifold vacuum. The pins come in different lengths to adjust or modify the shift feel. Adding a stronger spring or a longer or shorter pin will cause a firmer or softer shift. Throttle position sensors and manifold absolute pressure sensors indicate engine load and have replaced the modulator in today's electronically controlled transmissions.
Most Throttle Position Sensors are also adjustable. Rotating the sensor left or right will change the signal sent to the TCM. These sensors affect throttle pressure. Hydraulically controlled transmissions use the modulator to indicate load, and modern electronically controlled transmissions use the TPS and MAP sensor.