I'm having trouble with the brakes on my all original 1951 1/2 ton. The pedal is firm if you hold hard pressure on it, but if you hold moderate steady pressure (as you would at a stop light) the pedal sinks slowly to the floor. When you pump the pedal it goes back to normal. I have had some mild fluid leaks at 1 rear wheel cylinder. I bled the brakes and it was no worse or no better. Could it be the master cylinder? When I bought the truck 7 years ago I replaced all wheel cylinders and all 4 rubber hoses at the wheels. Any help appreciated.
