My fiance has a 99 suburban that keeps dragging a brake up on the front driver side. Thought that the caliper had failed so I replaced that along with rotors and pads. Three weeks later it does it again. Jacked it up and the caliper piston was stuck engaged on the rotor. Then cracked the bleeder and nothing came out. Finally had to break the banjo fitting on the hose loose to release pressure. I thought maybe this proved that the new caliper was bad. Not the case it is dragging again with a new caliper. What could be the cause for this? Any advise into where to look now would be greatly appreciated.