[mud slut 350]

I have a very similar problem. I swapped in a d60 front and 14bff rear and breaks were fine after the swap. I put a 4 speed trans in and all i did was pull the mc and booster assy aff the firewall to clear the rod and pull the pedals out and put it right back in. I did not tilt the assy i had a buddy holding it up, I did not dissconnect any lines, I did not do anything but pull it off the wall and put it back on. Now my pedal goes right to the floor not much braking at all ,before i could lock up the fronts with ease, and there is a hissing coming from the booster and the engine idles up. Now i understand the booster leakin engine idle going up but that should not matter because it still does all the same (without booster hissing) if i dissconnect the booster and plug the line and go without power brakes. I have driven many box chevy trucks with bad boosters and i can still lock up the fronts if i snad on the brake. mine will not do that still goes to the floor. I have bled the entire system 3 times and no improvement. Im in afghan right now but when i get home im gonan get a new booster and mc and see how that works.