done many ATE with no problems ~~~ since you didn't mention why you are rebuilding, i'm assuming that the piston is frozen ?? and assuming this is a single piston caliper

if frozen ~~~ remove caliper mounting bolts and pads, leave brake hose connected ~~~ slide in a used brake pad and use brake pedal (hydraulic pressure) to push piston out ~~~ cover caliper with a rag to contain brake fluid splatter ~~~ if piston moves and bottoms out on brake pad, remove pad and replace with something thinner to allow the piston to come all the way out ~~~ IF THE PISTON DOESN'T MOVE, REPLACE CALIPER

with the piston out, remove brake hose at caliper and place on bench ~~~ remove the 4 bolts and split caliper ~~~ do not lose or damage the 2 sealing o-rings, they are not available ~~~ clean passages with brake kleen and using emery cloth clean the piston bore and the piston ~~~ blow dry ~~~ replace piston o-ring in bore and coat with clean brake fluid ~~~ replace piston, also coated with brake fluid, should be able to compress in bore by hand, install boot and clamping ring ~~~ coat caliper half o-rings and torque the 4 bolts ~~~ mount on car with pads and bleed

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1989 300ce smoke silver / brazil, in a constant state of flux ~~~