The present invention relates generally to hydraulic systems for actuating a vehicle braking system. More specifically, the present invention relates to a hydraulic system that uses the gravity generated pressure in a load-bearing hydraulic cylinder (22) to provide hydraulic pressure to a service brake (34) or other service use when properly modulated. The present invention further relates to a system to reduce through dissipation or utilization the available gravity generated hydraulic pressure so as to deploy a ground engaging drag-brake of a vehicle.
