Re: How to Clean Engine, Brake Rotors and Calipers?
When painting cast iron, may I add my suggestions? After you get off all the rust you can, use a degreaser, and when that's dry, a liberal coat of phosphoric acid.
Phosphoric acid is the active ingredient in Naval Jelly. It converts any remaining iron oxide (rust) to iron phosphate, which is inert. It turns the cast iron a uniform grey as it dries, and you prime and paint right over that.
Edit: Just to be clear, do NOT use this on the working surfaces of the rotors, which should NEVER get anything but degreased.