[curtis73]

What you describe are classic symptoms of a bad master cylinder. The internal seals fail and let fluid past instead of compressing it in the lines. You won't see any leaks, and the braking will come and go. Often times you'll have to "pump" it several times and one of those times you'll get a seal and it will provide braking.

There are two circuits in the master cylinder. One controls the front brakes and the other controls the rear. They never fail at the same time. What may seem like no braking is just a funny sinking feeling when the pedal drops toward the floor. If you keep pressing, you'll eventually get braking on the other circuit, but of course at a highly reduced effectiveness.