I rebuilt my 2005 Ford Explorer Sport Trac front passenger brake caliper, and although the new pistons installed hard they went in. I moved on to the driver side removed the caliper cleaned it up, and painted it. Now I cannot get either piston to install (no paint in the piston bore nice and clean). I've got one piston half in using a block of wood, and a "C" clamp. It went in pretty hard. I had hoped that at some point it would start to push easily, but no. I lubed the inside square cut "O" ring, and the outer dust seal liberally with brake fluid. I rolled the new piston in brake fluid, but it will not go in. I have broken the new dust seal on the piston before it would insert. Now I have the other piston half installed so I am in no mans land. I cannot put air pressure to remove it since one piston is removed. It's not on the vehicle so it's not pressure from the vehicle and the bleeder screw and the brake line are disconnected and open. I did try to install without the dust seal, and the trouble is getting the piston to slide by the cut O ring. When I started to reassemble I first installed the cut O ring then the dust seal, and the piston last. I was thinking maybe I should install the O ring then slide the dust seal half way on to the new piston, and then try to install the piston. P.S. I compared the old O ring and piston, and they look the same. The only thing I have not tried is to reinstall the old piston using the old O ring just to see what happens. Any thoughts ? Yes before anybody suggests: If I had to do it over I would buy replacement calipers and be done with it, but I wanted to try it at least once, and I've got all the parts and pieces.