What was found
AFTER ENGINE START LOW BRAKE PRESSURE ANNUNICATOR CAME ON. I RESET THE "PWR BRKS" CB IAW THE CHECKLIST. WE ATTEMPTED TO TAXI, BRAKE PEDALS WENT TO THE FLOOR. RED EMERGENCY HANDLE WAS PULLED TO STOP THE ACFT. . TROUBLESHOT TO AND REPLACED POWER BRAKE SYS HYD PUMP ASSY MOTOR AND COUPLING WITH A REPAIRED MOTOR AND NEW COUPLING. OPS CHECKED GOOD. BLED BRAKE SYS AND SERVICED EMERG GEAR/BRAKE BOTTLE TO FULL. TAXI CHECKED GOOD. NO FURTHER DEFECTS NOTED. WORK ACCOMPLISHED IAW MM 32-44-20, 32-44-00, 12-13-01.