3-4 Accumulator
WARNING: This page is about a different car, the 2004 Pontiac Sunfire, 2004 Chevrolet Classic, and 2004 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
The fourth band fluid exhausts from the accumulator. A combination of spring force and 3-4 accumulator feed fluid pressure moves the accumulator piston to the Third gear position.