If I knew, they'd be fixed. It feels like there is air in the front, no matter how much I bleed. We blocked off the master after I replaced it several times, and it's fine - we blocked off the fronts and the rears feel 100% solid as well. Booster and master are brand new, calipers and pads and flexible hoses are brand new - the only thing left is the hard lines and stock porp valve & distribution block. All connections have been checked and tightened and none appear to be leaking. Pressure bleeding = no air, bleeding by hand (mac tilton) = no air, vacuum bleeding, I think I did get a little more air out initially (hard to tell since you have to retape the bleedscrews every 10 minutes) - but I'm not sure, no more came out and the pedal still just as bad. We tried unplugging the calipers and plugging the lines, and bleeding them out, and the pedal still felt just as bad, so I might be able to rule the calipers out if we really had all the air out of the ends after doing that. It's hard to tell without bleed screws.
I'd guess it was a leak but I can't find any fluid anywhere. Stock brakes were working perfectly before I took them off.