Years ago I made a tool to rotate the piston to push it back in.....but, why does it have to be done this way....I mean, why not open the bleeder screw and push it in with a clamp?

Well, because you'll basically destroy the caliper if you do it that way.

 

There's an extremely coarse threaded piece that is held to the back of the piston by a somewhat thin strap of steel, which can rotate in it's groove in the piston. This is part of the E-brake system, and is actuated by the movement of the E-brake lever on the caliper, which forces the screw-like piece against the piston, which is the pushed against the brake pads.. If you just applied linear force to the piston to push it back in the bore, I think you would strip-out that thin strap of steel, or damage the screw (if I can call it that). These 2 pieces act like a self-adjuster for the E-brake system to compensate for wear of the brake pads.

If you open the bleeder, then rotate it it moves alot easier. Just remember to bleed the system when your done. Tim

I like tools....now are you just saying that because tools are in the room....I like tools