Abstract: A fluid coupling device is disclosed of the type having an output coupling assembly (13) and an input coupling member (11). Control of the flow of viscous fluid between a reservoir chamber (35) and an operating chamber (33) is by rotation of a valve arm (43), to cover or uncover a fill opening (45). Rotation of the valve arm is affected by an actuator assembly (61). A raised portion (79) on a plate (73) attached to an armature (67) biases the valve arm (43) into sealing engagement with a surface (31) which defines a fill port (45,89), thus reducing fluid leakage from the reservoir (35) back into the operating chamber (33). A portion (85) which covers the fill port includes a dimple (91) which is disposed within the fill opening when the valve arm is in its closed position (FIG. 5). As the valve arm begins to move toward its open position (FIG.

Abstract: A hydrostatic transmission system is provided which is particularly well adapted for use in driving vehicles employing skid-steer drives. In the system disclosed two independent hydrostatic transmissions, each employing a variable displacement motor are utilized; and a pressure responsive valve is employed to sense the magnitude of the load on each of the motors and to permit shifting the motors from minimum displacement toward maximum upon the sensing of a load in excess of a predetermined valve. The variable displacement motors of the system are configured to create forces during operation tending to urge the motors to maximum displacement, and the pressure responsive valve operates to bias the motors to minimum displacement when they are loaded at a magnitude less than the predetermined valve.