Abstract: A unitary braking system for a towing vehicle and a towed vehicle in which a pneumatic pressure force is added to the towing vehicle's master cylinder generated pressure force for applying the towed vehicle brakes during normal operation, and, upon loss of pressure in the master cylinder brake system due to unintended separation of the towing vehicle and towed vehicle the towed vehicle brakes are automatically applied by a spring controlled or other preloaded mechanical force applied to the towed vehicle's brake system.