calipers not attached. these are toyota calipers. is there a coating on the calipers or is it raw cast metal? i have used a stainless wire brush, gunk engine foaming degreaser, and brake parts cleaner, and simple green. cant get the baked on brake dust in the inside calipers. they are not from the rust belt so no rust at all. are there other solvents i could try? i want to clean as much as i can before taking out the pistons to rebuild.