Tore down the front wheels on this e150 I just bought and never seen pad wear like this - its diagonal. Lengthwise, along the pad, its face is worn at a slope, from not much left of the pad material at one end, to almost all the pad material left on the other end. Never seen a piston act this way. Im guessing the piston is to blame, for putting more pressure on one end of the pad, rather than the entire surface of the piston....

what do you guys think? Or is this normal for E150 disc brakes up front?

 

I could be wrong on this, but I would suspect your vehicle has a frozen caliper pin. It's not an uncommon problem. Those pins should be removed and the bores cleaned and lubricated on every pad replacement . They do require special lubricant that will not attack the protective boot that is supposed to keep unwanted contaminants out. Ford for some reason doesn't have squealers on the pads and by the time you hear or feel the grinding of metal to metal on the rotors it too late and rotors are usually required when pads get replaced.