Have been battling this problem myself for a few weeks...and realizing I just missed the annual Northeast meet up, and am about to miss 2 more car shows... I think I have finally tried everything I can personally think of -- I need help!
Long story short, I hope: Front right caliper was dragging a little bit, figured I'd rebuild before it got worse. Took the caliper off and lost a bit of fluid, still plenty in the master cylinder. Had trouble getting the pistons out, so ended up using the "grease gun trick", not recommended but it worked. Cleaned up the caliper with tons of brake clean, put in new seals, pressed pistons back in, indexed them and bolted it back up. Then the saga of bleeding:
1. Did the "two man" brake bleeding method at first on just the rebuilt caliper...and couldn't get a hard pedal.
2. Did "2 man" on all 4 calipers -- pedal still soft.
3. Put on the Motive power bleeder, burst a hose on the motive...cleaned up a fountain of brake fluid
4. Actually bled all 4 with the Motive (new hose) -- pedal still soft.
5. Drove around the block, had to pump the brakes like heck to stop -- no change.
6. Had a friend 'pump up' the brakes and then 2 man bled the fronts -- no change.
Other relevant facts:
A. Before I started this adventure, I had a great hard pedal.
B. Brake fluid squirts out of all calipers when I bleed, so I don't suspect a master cylinder issue (should I?)
C. Rear brake pads are worn on one side, but seems unrelated...again pedal was great.
So, what the heck am I forgetting??