if one of your pads is significantly worn, most likely you have a frozen slider. Take them apart, and there should be two slide pins on each caliper bracket. They should move in and out freely. If they don't, then you need to get them out and grease them up. If you can't get them out you need a new caliper bracket. If the piston on the caliper itself is frozen, or it looks like the boot is torn, then you need a new caliper as well, which will usually come with a new bracket and slide pins.