This requires a special tool which spins the piston clockwise and simultaneously presses the piston in. This is do to the park brake system being incorporated into the caliper. If you can fashion a method to turn the piston with the notches on the face (portion that contacts the brake pad) and then push, turn, push, turn, etc. You may be able to get it in. This has the two V notches and will be difficult without the special tool. DO NOT scratch the sides of the piston as this is the sealing surface, and will then require replacement of the caliper.