A hydraulic circuit for a vehicle having at least one selectively actuated hydraulic assist motor. The hydraulic circuit includes a first loop that includes, in serial order, a first hydraulic pump, a first hydraulic line, at least one hydraulic motor and a second hydraulic line. A second hydraulic pump and a third valve is used to control the flow of low pressure fluid from the second pump to the hydraulic motor casing. The low pressure fluid through the third valve maintains the motor pistons retracted when the motor is not being used. For actuating the motor, the third valve is actuated for disconnecting the second pump and relieving pressure from the motor casing. Low pressure is then provided to the first and second lines for extending the motor pistons. The first and second valves are then actuated for isolating the first and second lines from one another, and the first pump is used to power the motor. The first, second and third valves are advantageously solenoid cartridge valves.