explorer 8.8 in an a-body: experience needed

RedFish said

The only retract action in a disc brake caliper is caused by a square ring instead of an O ring. If a rotor has enough runout to push a piston back into the caliper that rotor needs to be replaced.
There is a small amount of residual pressure in every antilock brake system. It isn't enough to heat parts, accerate lining wear, or cause any other ill effects.

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The rotor always has enough movement to push the piston further in than it should be, and this is why residual valves are made in such slight psi increments.

Who's dart here has anti lock brakes ?

Why is it when i install disc's on jeeps with antilock brake systems that also had disc drum that they also NEED a residual valve ?
Antilock brake systems aren't residual valves and they don't hold a minute amount of psi against the rear calipers.

Every car that someone adds discs to has always needed a RV and they ALL had the same problem, unless EVERYTHING was changed and done correctly from the specific master back.