For those that don't know, the only thing that retracts caliper pistons is a slight rotation of the square O-ring. There is no spring return. It works amazingly well, but only if the piston is free to slide. Some of the earliest front calipers on 60's Mustangs and Darts would get stuck from rust, which is how after-market Stainless Steel Brake Company got their start.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans