I have an amphibious vehicle, and all of the brake parts get completely
> immersed. I'm going to be doing a very complete brake job soon, and I want
> to protect all the internal metal as well as possible. Would it be OK to
> paint all the internal exposed metal surfaces (obviously not the drum ID's)
> with something like POR-15?
Might want to use the POR-15 high temp paint. I've used that on the rear calipers of my mustang and engine block paint on the front drums of my maverick without any problems. external surfaces, though the internal surfaces stay nice and clean. Even basic krylon has worked on backing plates and the like.