I've been having issues with parking brake not releasing on the driver's side. Pulled caliper today. Arm would not release. Removed spring, blasted and cleaned around the parking brake arm, moves much more freely now. The problem I have is I don't think the inner piston is retracting appropriately, if at all. See picture below. That doesn't look fully retracted to me. The inner adjuster will push the piston further out of the bore, but I can not get it to retract the piston back into the bore. Can I use a clamp to retract the piston or is that a BAD IDEA? Has the piston come off the end of the adjuster, or is that possible? Scratching my head here.
Thanks,
Aaron

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Looks like a rust issue from the pictures.

Pop the circlip and carefully remove the dust boot, check for rust and clean up the piston circumference (if its not too badly pitted) with it wound out, lightly grease and then try pushing it back in (with the adjuster fully wound back).

Otherwise it's pop it out completely, new piston, seals and clean up.

Send them to Eric at PMB. Does beautiful work and is very helpful.

That's where these came from, MANY years ago. Another question. Does the inner piston possibly not retract as far into the body as the outer one? I have an old caliper I have been playing with and the adjuster seems to work fine on it, but the inner piston doesn't retract "flush" like the outer one does. Is the inner piston supposed to retract "flush" with the body/bore?