another way to do it would be to leave the old inner pad in place and push against that. I personally find that Vise Grip C-clamps work better than using the screw down type, they're faster and much less work. Just clamp it down, let it push the piston in, tighten more, clamp, repeat until the piston stops in the bore. Another tip that will help, open the bleeder screw. That way, you're not pushing any dirty fluid back into the master cylinder.
