so i was going to change my brake pads today, I moved the pistons back removed the pads then I pumped the brake handle to make sure everything is ok...when i pumped the brake only the upper piston would move... before I go buy a used one somewhere I just want to make sure both are supposed to move.  thanks

If you hold the piston that is moving does the other one move when you squeeze the lever?

-Jessie

Do what Jessie says. You might need something to hold on the moving piston, the old pad might help here.

You should also take an old toothbrush, hot (why not) water and some mild soap and clean the caliper. Then apply some brake fluid on the pistons and slide them in and out several times. This will probably help except if the seals are toasted.

http://www.youtube.com/watch?v=1Yo80Bm8L7w