I have a 79 F-250 4x4 and the brakes just got really bad all of the sudden they have been great but recently the pedal goes to the floor almost and I can not stop very well. I bled the brakes when I bought the truck and I could stop on a dime but just recently it just feels like there is nothing there. I am wondering if the master cylinder is bad since both front and rear seem to have gone bad at the same time. thanks in advance for any help.