If the caliper still doesn't come off you might try looking at the caliper on the opposite side. Might help to determine what is going on.

Personally, when I replace calipers I replace both sides at once. Matched calipers (with respect to wear, rust, intrusion) stand less of a chance of uneven performance. After the brake work, if you find you're pulling to the side of the new caliper when you brake, replace the other one.

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Stay the Trail!