What was found
PILOT REPORTED, THE BRAKES FAILED ON THE CAPTAIN'S SIDE, BOTH PEDALS. CYCLED THE BRAKE ANTI-SKID SWITCH WITHOUT RESTORING THE BRAKE EFFECTIVENESS. THIS WAS THE SECOND OCCURANCE OF THE SAME PROBLEM ON THE SAME DAY. MAINTENANCE FOUND THE NR 4 MAIN LANDING GEAR TIRE CAP TO BE LOOSELY FITTED TO THE ANTI-SKID TRANSDUCER. REPLACED THE TIRE CAP, ALL OPERATIONAL CHECKS GOOD. THE AIRCRAFT WAS RELEASED WITH NO FURTHER PROBLEMS.