AN ERROR IN THE INSTALLATION OF THE BRAKE AIR LINE RESULTED IN CONNECTING THE FRONT AND REAR AIR BRAKE SUPPLY TANKS IN SERIES WITHOUT A CHECK VALVE BETWEEN THEM. IF AN AIR LEAK DEVELOPS IN EITHER THE FRONT OR REAR BRAKE SYSTEM, BOTH TANKS WOULD BE DEPLETED OF AIR CAUSING BOTH BRAKE SYSTEMS TO BE INOPERATIVE. CONSEQUENCE OF DEFECT: A TRUCK WITHOUT INDEPENDENT FRONT AND REAR BRAKE SYSTEMS IS IN NONCOMPLIANCE WITH FMVSS 121, AIR BRAKE SYSTEMS, WHICH PROVIDES SUCH A SYSTEM TO REDUCE HIGHWAY ACCIDENTS.
REWORK PLUMBING FOR BRAKE LINES TO ENABLE FRONT BRAKE SYSTEMS TO BE INDEPENDENTLY FILLED AND PROTECTED FROM REAR BRAKE SYSTEM.
SYSTEM: AIR BRAKES, FMVSS 121.VEHICLE DESCRIPTION: HEAVY DUTY TRUCKS.