What was found
LOW BRAKE PRESSURE AND ANTI SKID INOPERATIVE ILLUMINATED DURING TAXI , EMERGENCY BRAKE HANDLE WAS USED TO STOP ACFT MOVEMENT . AFTER ENGINE SHUTDOWN, NOTICED BRAKE ACCUMULATOR MOTOR WAS NOT RUNNING WITH BATTERY SWITCH ON AND CIRCUIT BREAKER CLOSED. AFTER 30 MINUTES, TURNED BATTERY SWITCH ON TO DO POST FLIGHT AND NOTICED BRAKE MOTOR RUNNING BUT WITH GRINDING NOISE. PRESSURE DID BUILD UP BUT TOOK ABOUT FOUR TIMES LONGER THAN NORMAL. TROUBLESHOT AND COULD NOT DUPLICATE. CALLED MANUFACTURER AND THEY SUGGESTED CHANGING MOTOR & PRESSURE RELEASE VALVE. REMOVED AND REPLACED POWER BRAKE MOTOR WITH AN OVERHAULED UNIT. INSTALLED A NEW PRESSURE RELIEF VALVE. SECURED GEAR/BRAKE BOTTLE AND BLED BRAKES. ALL OPS, LEAK & TAXI CHECKED GOOD IAW MM 32-42-06 & 32-42-00.