General Information
Warning: Freightliner Custom Chassis Corporation (FCCC) neither recommends nor approves connecting a trailer or other towed vehicle's braking system directly to the vehicle braking system. FCCC also neither recommends nor approves tapping into the vehicle air brake system nor operating a towed vehicle or trailer's braking system by means of the vehicle braking system. Failure to observe this warning could result in personal injury or death, or substantial property damage.
A dual air brake system consists of two independent air brake systems which use a single set of brake controls. Each system has its own reservoir, plumbing, and brake chambers. The primary system operates the service brakes on the rear axle; the secondary system operates the service brakes on the front axle.
Warning: Do not operate the vehicle with the front brakes backed off or disconnected. Backing off or disconnecting the front brakes will not improve vehicle handling and may lead to loss of vehicle control, resulting in property damage or personal injury.
The parking brake will apply when air pressure drops below 20 to 45 psi (138 to 310 kPa). Do not wait for the brake to apply automatically; when the warning light and buzzer first come on, immediately bring the vehicle to a safe stop. Before continuing operation of the vehicle, correct the cause of the air loss.
Air Brake System With External Fill (Schrader) Valve
Before a vehicle with insufficient brake system air pressure can be moved, the parking brake must be released by applying an external air source. First block the wheels, then turn the ignition switch to the ON position, then fill the appropriate system air reservoir using the Schrader valve on the inlet side of the air dryer. The parking brake will not release until air pressure reaches 65 psi (448 kPa). The low air buzzer will sound until air pressure reaches 65 to 73 psi (448 to 503 kPa) with the ignition switch in the ON position.
Important: If the air pressure in the braking system drops below 20 to 45 psi (138 to 310 kPa) the parking brake will reengage.