I put new lower and upper ball joints on a grand marquis (98 4.6 abs trac control) on the passanger side when the lower ball joint completly failed, the control arm was on the ground, when i got it all back together i had soft brakes, so i checked the flexable brake line on the passanger side and it was good, even while someone was pressing the brakes so i could see if it bubbled up, so i gravity bleed the brakes all around farthest to closest the the MC, peddle felt harder than before, so i started it up and took it for a test drive, and soon the peddle was soft again, and i only had back brakes, so i looked for leakes and couldnt find any, so i gravity bled again( a few times) i also made sure there was enough fluid in the MC, still no front brakes, what could it be? im thinking it could be a issue with trying to bleed and the abs is messing me up? do i need a special tool? could be a bad seal in the piston in the caliper? bad MC? the brakes were fine before the ball joint failure

 

had an issue like this before with one of my Neons and it ended up being the master cylinder. But you said the control arm was on the ground, if it happened while you were driving and it drug then I could see the forces applied to doing something to the caliper. Have you taken the caliper apart, or least the brake pads off and visually inspected it?