First question is: 1. Is the pedal fading to the floor and the 'hard' you are describing is just that the pedal is at the floor? When replacing a master cylinder on these Fords, it can be a pain to properly 'bleed' the master cylinder and then the complete brake system. You don't mention the results from your bleeding after replacing the Master? Below is one of my videos on Master Cylinder Bleeding and my YouTube channel @Caddyman has a host of other videos dedicated in a Playlist to the repair of this 1991 F250 4x4 7.3l IDI. Enjoy.[br]
https://youtu.be/51vcS0-FTAU?si=eTNJE7j0hoATA2jx[br]