Bled the Master Cylinder again and all brakes and LPSV -- Trying to get the truck ready for a friday trip. . . . not looking too good. I press the pedal down halfway, and everything is fine - I'm stopping with a firm pedal. Then I press a little harder and then it seems like I break through something, hear a clunk, the pedal goes all the way down and I lose my brakes! Very freaky. If I'm really careful, I have good brakes Just don't press them too hard.

Any idea what's goin on here?

 

I'm sorry to say, but it sounds as though you've a bad master cylinder.

If you'll type "master cylinder" into the "Search" window that pops open when you slide your cursor across it you'll find complete instructions on how to test it, as well as info in replacing it.