What was found
PILOT REPORTED DURING TAXI OUT, BRAKES BECAME UNRESPONSIVE & ACFT VEERED LEFT. SHUTDOWN ACFT. NO DAMAGE OR EVIDENCE OF ANY FLUID LEAKAGE PRESENT. TROUBLESHOT BRAKE SYS, CHECKED BRAKE LINES, MASTER CYLINDERS, HYD RESERVOIRS & PERFORMED FUNCTIONAL CHECKS. COULD NOT DUPLICATE MALFUNCTION. R & R BRAKE MASTER CYLINDERS AND PERFORMED ALL FUNCTIONAL AND OPS CHECKS IAW MM 32-40-00.