Malibu Mod.1998 rear brake problem

The problem is that my son stayed without brakes since one of the tap brakes (rear) is thrown away when one of the tires was done from their place of (piston) the balatas were very worn even the drum My question is to serve the piston or I have to change it I appreciate your attention to my problem waiting for your opinion in this regard God bless you.

If the bells are very rectified, the tapes must be overmed, that is, the component that Rozo on the bells (ferodo) must be of greater thickness so that the piston is not disarmed; Even when rectifying the bells are with a different radius to the original radius of the tapes.