is there something i have to do before i can push the piston back in on the rear brakes on a 4 wheel disk brake system....i tried opening the bleeder screw and pushin the piston back in with the tool but it wont move.

 

That is not what the bleeder valve is for. You only need to remove the cap from your brake fluid resivore.

The trick with the rear caliper piston is that you have to "screw" it back into the boar. It has something to do with the parking brake. Use some needle-nose pliers, stick them in the cross shaped grooves in the piston & twist it in like a big screw. If it's too hard to turn with pliers, the blade end of a crow-bar works too (I've used one). Hope I made it in time to help you out...