WHEEL FIRE ON A PA28A AFTER TAXIING TO THE RWY END FOR RUN-UP.

Narrative

WHILE TAXIING TO RUN-UP AREA; BRAKES WERE INOP. IMMEDIATELY CLOSED THROTTLE AND MIXTURE; COASTED TO STOP. SMOKE VISIBLE UNDER R WING. IMMEDIATELY EXITED ACFT. WHEEL PANT ON R STRUT ON FIRE. CALLED ARPT FOR FIRE TRUCK; THEN NOTICED L WHEEL PANT ALSO ON FIRE. FIRE TRUCK ARRIVED; FIRES EXTINGUISHED. CAUSE AT THIS POINT UNKNOWN. ACFT CURRENTLY LOCKED IN MY HANGAR UNTIL INSURANCE ADJUSTER AND AT LEAST 1 OTHER A&P/IA EXAMINES FOR POSSIBLE CAUSE. NOTE: ACFT IN SHOP 2 WKS EARLIER FOR BRAKE SVC. ONE POSSIBILITY IS CALIPERS OR BRAKES (HAND BRAKE) SET; ALTHOUGH IT'S UNLIKELY THE BRAKES WERE SET. NO ONE HURT; NOT EVEN UPSET. DID EXACTLY WHAT CFI AND LESSONS IMPRESS UPON ME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE BRAKES HAD A HISTORY OF LEAKS OVER THE PAST YR. THERE WAS MAINT DONE 3 DIFFERENT TIMES DURING THAT PERIOD. LAST WORK WAS A BLEED OF THE BRAKE SYS 2 WKS PRIOR TO THE FLT IN QUESTION. THERE WAS NO EXCESS PWR REQUIRED FOR TAXI; HOWEVER; INSURANCE AND MAINT INVESTIGATORS SURMISE THAT THE PARKING BRAKE WAS NOT COMPLETELY RELEASED; CAUSING HEAT BUILDUP; RESULTING IN THE BURNING OF THE HUB CAPS ON BOTH WHEELS.