if the piston went back in without losing any parts like the rubber seal that is around it then you should be able to bleed the brakes and get back in business. reassemble the caliper with the pads, have someone pump the brake pedal til it is hard then hold it firmly. you loosten the brake bleeder valve and let out fluid til the pedal is on the floor. shut the valve off and have them pump it up again. do this til there are no bubbles coming out when you release the bleed valve. then test drive. if the pedal feels normal you are fine. if the pedal will pump up after starting too low, you need to bleed again. keep a close watch on the resorvour to be sure you dont run low on fluid in the process taking care to note that there are two compartments in it that both need to be full. allowing one to get dry will reintroduce air into the line.

good luck. check back if you have any questions. dont drive car if the pedal doesnt feel right.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.