THEORY OF OPERATION - CONTINUED
BRAKE SYSTEM - CONTINUED
The warning light and buzzer inside the cab are activated if air pressure drops below 64
psi (441 kPa) in either brake system. If this happens, check air pressure gages to deter-
mine which system has low air pressure. Although vehicle speed can be reduced using
the foot brake control pedal, either the front or rear service brakes will not operate, result-
ing in a longer stopping distance. Bring vehicle to a safe stop and have the air system
repaired before continuing.
If the primary brake system becomes inoperative, the spring parking brakes 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 M915A3 has automatically adjusting slack adjusters. On all axles, brake chambers
have a stroke alert indicator which allows the operator to monitor brakeshoe wear.
REAR AXLE SPRING