Brake System. The main brake system components consist of the service brake
pedal (1), six brake chambers (2) on axles # 3, # 4 and # 5, eight brake chambers (3) on
axles #1 and #2, and a parking brake valve (4). When the service brake pedal (1) is
depressed, air is supplied to all the brake chambers (2) and (3), applying the service
brakes. The parking brake valve (4), applies or releases the rear axle (parking) brakes.
When air pressure in the brake system drops below 30 psi (207 kPa), the rear brake
chambers (2) automatically apply.