Ford F-650 Owner's Manual page 115

WARNING: Block the wheels to help prevent the vehicle from
moving.
WARNING: Unexpected and possibly sudden vehicle movement
may occur if these precautions are not taken.
Loosen the jam nut (1) and un-thread the adjustment rod (2) from the
chamber to reduce tension on the cable (3). Continue to un-thread the
adjustment rod all the way and remove it from the chamber. The nut and
shaft are metric.
AIR BRAKES (IF EQUIPPED)
General air brake information
After starting the engine, give the air compressor time to build up the air
pressure to 60 psi (414 kPa) before moving the vehicle.
WARNING: Do not drive or continue to drive if the low air
pressure buzzer is sounding or the brake warning light is lit. These
warnings indicate that air pressure is not to normal operating level.
Continued use of the vehicle could result in loss of braking ability.
WARNING: Avoid repeated light application of the brake pedal.
This depletes air pressure faster and could result in loss of
braking capability.
2012 F-650/750 (f67)
Supplement, 2nd Printing
USA (fus)
Driving
115