Thank you for asking your question on JustAnswer. The rear calipers must be compressed using the proper tool, trying to compress with a C-Clamp may have damaged the caliper, if you need I can send instructions directly from Ford on how to perform the repair.
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Thank you for asking your question on JustAnswer. The isntructions with diagrams are below. Hopefully the caliper is not damaged, you may also try loosening the bleeder screw to relieve the pressure, and help the piston compress. To move the piston back into the caliper, the LH piston is turned clockwise and the RH piston is turned counterclockwise.