#2 Checkball (Second Clutch Apply)
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 2-3 drive fluid seats the #2 checkball, forcing the 2-3 drive fluid through the #3 orifice and feeding the second clutch fluid circuit. the #3 and the #4 orifices help to control the apply feel of the second clutch.