WHILE DRIVING IN STOP AND GO TRAFFIC IN SOUTHERN CAL. THE TRUCK IN FRONT OF ME STOPPED SUDDENLY. WHEN I PUSHED ON MY BRAKE PEDAL IT WENT ALL THE WAY TO THE FLOOR. THE ONLY THING THAT STOPPED ME WAS THE TRUCK IN FRONT OF ME. THIS BREAK PEDAL THING HAPPENED ONCE BEFORE BUT WITHOUT AN ACCIDENT. DURING THE TIME OF THE ACCIDENT MY SPEED WAS ABOUT 20MPH IN DRY CONDITIONS. I HAVE A 2001 FORD F-150, 4.2 V-6 , SUPER CAB, 4X2, AND AUTO, WITH 50K MILES. I HAVE REPLACED MY MASTER CYLINDER HOPING THIS WILL CORRECT THE PROBLEM. I SAVED THE OLD CYLINDER AND WOULD BE HAPPY TO SEND IT TO YOU ALL FOR INSPECTION. I TOOK IT APART MYSELF AND FOUND FOUR SMALL SCRATCHES ON THE HOUSING. *LA