The warning light and buzzer inside the cab come on if air pressure drops below
64 psi (441 kPa) in either system. If this happens, check the air pressure gages to determine
which system has low air pressure. Although the vehicle's speed can be reduced using the
foot brake control pedal, either the front or rear service brakes will not be operating, causing a
longer stopping distance. Bring the vehicle to a safe stop and have the air system repaired
If the primary system become inoperative, the spring parking brakes will
automatically apply when air pressure drops to 35-45 psi (241-310 kPa).
The vehicle has a four-channel anti-lock brake system (ABS) and cam-operated
service brakes with non-asbestos brakeshoes.
The M915A4 has automatically adjusting slack adjusters. On all ax les, brake
chambers have a stroke alert indicator which allows the operator to monitor brakeshoe wear.