NHTSA complaint: 2003 MACK CV — SERVICE BRAKES, AIR:DISC:CHAMBER
THIS VEHICLE IS A 2003 MACK TRUCK MODEL CV AND IS A STRAIGHT FRAME DUMP TRUCK WITH THREE REAR TANDEM AXLES. STOPPING IS ACHIEVED THROUGH A STANDARD AIR BRAKE SYSTEM WHERE COMPRESSED AIR IS USED AS THE ENERGY MEDIUM. THE BRAKE PEDAL EFFORT OF THE OPERATOR IS USED ONLY TO MODULATE THE AIR PRESSURE APPLIED TO THE BRAKE CHAMBERS. THIS TRUCK CONFORMS TO THE DUAL BRAKE SYSTEM. ALTHOUGH THE ENERGY SOURCE IS COMPRESSED AIR, THE TRANSMISSION OF ENERGY FROM THE BRAKE CHAMBER TO THE FRICTION SURFACES INVOLVES LEVER ARMS AND CAMS. THE COMPRESSED AIR IN THE SPRING BRAKE CHAMBER MAINTAINS PRESSURE ON THE SPRING DURING NORMAL OPERATION. WHEN THE BRAKES ARE ACTIVATED, THE AIR IS RELIEVED ALLOWING THE SPRING TO DECOMPRESS AND APPLY THE FRICTION SURFACES TO THE DRUMS THROUGH THE MECHANICAL LINKAGE. THE FIRE PATTERNS INDICATE THAT THE FIRE WAS LOCALIZED AND ORIGINATED FROM FRICTION PRODUCED BY THE BRAKE PADS AGAINST THE DRUM ON THE CENTER RIGHT REAR TANDEM WHEELS. THE FRICTION PRODUCED TEMPERATURES IN EXCESS OF THE IGNITION TEMPERATURE OF THE TIRES CAUSING THEM TO IGNITE. THERE WAS NO PHYSICAL EVIDENCE OF ANY ELECTRICAL FAILURE. THE SPRING BRAKE CHAMBER IS IDENTIFIED AS MGM 3431157, M092702, 190E 4100 P7. CONCLUSION THE FIRE WAS LOCALIZED AND PRODUCED BY FRICTION. THE FRICTION RESULTED FROM THE BRAKE PADS AGAINST THE DRUMS OF THE CENTER REAR RIGHT TANDEM BRAKES. THIS FRICTION PRODUCED SUFFICIENT TEMPERATURES TO IGNITE THE TIRES. THE APPLICATION OF THE BRAKES THAT PRODUCED THE FIRE RESULTED FROM
National Highway Traffic Safety Administration — Office of Defects Investigation