Coupling device and improved fluid pressure system therefor

A coupling device of the type including a clutch assembly actuation of which is responsive to fluid pressure in a clutch piston apply chamber, and a series of fluid passages communicating the chamber to a control valve assembly. A housing defines a hub portion surrounded by a plenum member carrying two high pressure seals. The housing is formed such that the outer surface of the hub portion is free of graphite porosity, to improve the life of the seals. Preferably, each of the seals has a height/width ratio selected to provide the desired radially inward sealing force, but wherein the seals are still able to be assembled within the respective seal cavities.