Abstract: An apparatus for the compression of a piston of a disk brake housing into a cylinder includes a caliper gun frame, a lever attached to the frame, a rod that extends forward and away from a user as the lever is squeezed, a hollow extension shaft attached to the frame and disposed over a portion of the rod, a retaining plate attached to a distal end of the extension shaft, a compression disk attached to a distal end of the rod and an actuating assembly attached to the frame and affected by the lever that displaces the rod in a first forward direction as the lever is squeezed. The device is positioned intermediate an inside surface of the housing and the piston whereby the compression disk bears against a top exposed surface of the piston and urges the piston into the cylinder as the lever is squeezed an amount sufficient to replace a pair of disk brake pads.