Patent ID: 7452038

Claim:
A method of releasing or applying a parking brake of a disabled vehicle having a service braking system and a spring applied parking brake system with a towing vehicle to facilitate towing comprising: providing a source of hydraulic fluid at the towing vehicle; supplying the source of hydraulic fluid to the spring applied parking brake system of the disabled vehicle and controlling the pressure of the hydraulic fluid to a specified level, whereby the supplied hydraulic pressure at the specified level releases the spring applied parking brake of the disabled vehicle, the controlling performed from the towing vehicle, and monitoring at least the pressure of the hydraulic fluid supplied to the disabled vehicle during towing, wherein the pressure in the hydraulic fluid being applied to the spring applied parking brake is controlled at two or more elevated pressure levels and hydraulic fluid at one of the two or more elevated pressure levels is supplied to the spring applied parking brake system so that disabled vehicles with parking brakes systems using varying parking brake system elevated hydraulic pressures can be towed, wherein supply of hydraulic fluid, controlled to the specified level, and applied to the spring applied parking brake of the towed vehicle from the towing vehicle is through single line and return of the hydraulic fluid from the towed vehicle to the towing vehicle is through the same single line.