You may also find that you can put the business end of a grease gun into the brake line fitting and force the piston out. Doing it with compressed air has always given me the jitters, but I try not to use high-caliber popguns in the shop.
crazypj said:BTW, does anyone know which GM car uses the 1.5" phenolic piston? ( I like the idea of lightweight, non corroding, low heat transference brake piston)