THE VEHICLE WAS PARKED ON A 35-40 DEGREE SLOPED DRIVEWAY. GOT IN, STEPPED ON BRAKE,STARTED VEHICLE, RELEASED EMERGENCY BRAKE, SHIFT INTO REVERSE, AND BRAKE PEDAL WENT TO THE FLOOR, WITH TRUCK ROLLING BACKWARDS. WHEEL WAS TURNED, AND TRUCK HIT A SIDE OF RETAINING WALL. IT DID NOT ROLL BACK EXCESSIVELY FAST, BUT IT COULD NOT STOP IN TIME TO AVOID HITTING THE WALL. FOUND BADLY CORRODED BRAKE LINES. ONE HAD RUPTURED RIGHT BEHIND THE DRIVER'S FRONT WHEEL FENDER WELL. *TR