You need a big piston up front to work with the Explorer caliper out back. Are you using the factory calipers up front? If you have room for a 11.75 rotor (15 inch wheel) you might want to upgrade the front rotors. All you should need would be the bigger rotors and the taller caliper brackets. You shouldn't even need to bleed the brakes, just lift the calipers off and change the rotors and brackets and drop them back on.