did u mount the calipers upside down? make sure that the bleeder screws on the calipers are on top and not on the bottom.
i learned this when i was 16 on my z. i bought new calipers,painted them and mounted them with the bleeders on the bottom so when i bled the they wont get dirty.i must have bled everything 10 times before i figured out that there was trapped air on top of the calipers......
check it out and let us know
p.s dont laugh at me i was only 16 8)