"P" Series Motorhome

WARNING: This page does not describe the selected car, but rather 35 other vehicles, including the 1992 Pontiac Trans Sport, 1992 Oldsmobile Silhouette, 1992 Oldsmobile Bravada, 1992 GMC Yukon, and 1992 GMC Vandura Special. However, it is still accessible from the selected car via links, so may be relevant.

On the automatic apply parking brake system, when shift lever is in Park, engine running, and manual parking brake foot lever in released position, fluid flows from steering gear to port SR on relay valve and out to port TW to the control valve supply port SC. See Fig 1. Once the system is charged, pressure should range between 130-150 psi (9.1-10.5 kg/cm² ). Any excess fluid will be discharged through port "R" and back to the pump. The supply port or charge port SC is blocked off due to control valve position in Park mode.

Any previously pressure built-up in control valve flows through control valve out port EC back through the relay valve, triggering release of pressure from port "D" of relay valve through port ER to reservoir. See Fig 1. This allows the spring controlled actuator to apply parking brake. The spring will apply brake by travelling as far as the brake adjustment demand requires to balance brake apply and spring force.

When valve is released from Park position, fluid charge at shift control valve port SC is diverted to port DC. The shift control port EC is blocked off. Fluid charge at relay valve port SR is diverted to port "D", pressurizing parking brake system and actuator. See Fig 1. Fluid pressure working against the spring pressure in actuator releases parking brake.

The manual foot lever should still be applied whenever vehicle is shifted into Park. This will alert operator of need for adjustment in the parking brake system.

NOTE: All figures in this article are Courtesy of General Motors.

Fig 1: Schematic Of Automatic Parking Brake System ("P" Series Motorhome)

Courtesy of GENERAL MOTORS CORP.