What was found
AFTER LANDING AND CLEARING THE RUNWAY IN FLO ON REPOSITIONING FLIGHT, THE A/C HAD AN UNCOMMANDED AND UNCONTOLLABLE TURN TO THE LEFT. NORMAL BRAKES WOULD NOT FUNCTION. CREW STOPPED THE AIRCRAFT USING THE PARKING BRAKE. AFTER ENGINE SHUTDOWN NR 4 TIRE WAS FOUND TO BE FLAT. REPLACED NR 4 MAIN WHEEL ASSEMBLY. REPLACED NR 4 BRAKE ASSEMBLY AS A PRECAUTION. INSPECTED AND OPS CHECKED ALL ASSOCIATED SYSTEMS, NO PROBLEMS FOUND. PERFOMED TAXI TEST AND EVALUATION FLIGHT, NO PROBLEMS FOUND. ANTI-SKID SYSTEM PLACED ON MEL FOR FUNCTION CHECK. ANTI-SKID FUNCTION CHECK FOUND NR 3 BRAKE WITH LOW PRESSURE. REPLACED THE ANTI-SKID DUAL CONTROL VALVE.