WHILE DRIVING APPROXIMATELY 35 MPH IN TOWN, THE VEHICLE IN FRONT OF ME SIGNALED TO MAKE A LEFT HAND TURN. I BEGAN TO SLOW DOWN THE VEHICLE AND THEN I LOST ALL BRAKE PRESSURE. I WAS UNABLE TO STOP THE TRUCK TO AVOID AN ACCIDENT DUE TO COMPLETE BRAKE FAILURE! THERE WERE NO PREVIOUS LIGHTS OR WARNING SIGNALS NOTIFYING OF A BRAKE PROBLEM PRIOR TO THIS. THE WARNING LIGHT CAME ON AFTER THE ACCIDENT. THE BRAKE FLUID RESERVOIR WAS FULL. AFTER FURTHER INVESTIGATION, IT APPEARS THAT THE BRAKE LINES WERE CORRODED CAUSING THE BRAKE FAILURE.