Low and Reverse Servo
WARNING: This page is about a different car, the 2010 Pontiac G5 and 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
Low band fluid is routed to the inner area of the servo piston. Low band fluid pressure moves the servo piston and pin assembly against a spring force in order to apply the low/reverse band.