I have a 1998 Ford F-250 3/4 ton. I just got done putting new calipers, disc, pads, and a rebuilt master cylinder, and have bleed all the lines (alot cant see any air bubbles). The pedal still wont get stiff, it drops right to the floor. what is going on?????

 

Did you bleed your master cylinder first?
If you didn't, I would thinkyou would see air bubbles.
View this link for the whole procedure.

http://autorepair.about.com/od/brake.../aa091804c.htm