You could fill pages and pages with all of the functions of an automatic trans valve body. It's the hydraulic "brain" for the trans. Do a search on vacuum modulator. You might find some interesting information.

__________________
Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.