What was found
DURING TAXI OUT FOR 135 LEG, CREW OBSERVED LOW BRAKE PRESS/ANTI-SKID M/C, NO BRAKE PRESSURE IN POWER BRAKE SYS, POWER BRAKE CB REMAINED IN, USED EMERGENCY BRAKE TO STOP ACFT ON TAXIWAY, SHUTDOWN ACFT. REMOVED FAULTY POWER PACK MOTOR ASSY AND INSTALLED AN O/H ASSY. SERVICED ACCUMULATOR & PRE DIED BRAKES AND ALL OPS & LEAK CHECKS GOOD AT THIS TIME. WORK DONE IAW MM 32-42-06.