CERTAIN BLUE BIRD MY 2004 THROUGH 2007 VISION SCHOOL AND TRANSIT BUSES MANUFACTURED BETWEEN OCTOBER 9, 2003, AND SEPTEMBER 21, 2006, EQUIPPED WITH PARKER SINGLE CHECK VAVLES (SCV) PROVIDED BY BENDIX. THE DEFECT EXISTS IN THE PARKER SCV THAT CONNECTS WITH THE SUPPLY PORT OF THE SR-7 SPRING BRAKE MODULATING VALVE. AFTER PROLONGED USE OF THE PARKER SCV, THE VALVE BODY RETAINER MAY BECOME EXCESSIVELY WORN AND EVENTUALLY BREAK APART. PIECES OF THE PARKER SCV CAN BECOME LODGED INSIDE THE SR-7 SPRING BRAKE MODULATING VALVE, POTENTIALLY CAUSING EITHER LEAKAGE OUT OF THE SR-7 VALVE OR PREVENTING AIR FROM PROPERLY EXHAUSTING FROM THE SR-7 VALVE.