just sand it down to bare metal and primer it then painted! or if you dont want to spend the time sanding i use this chemical that changes the rust into a black mineral and you cant paint straight over that, dont have the bottle in front of me but any paint store sells it.. and also on my drive shaft i used rust destroyer spray primer guaranteed to work on rust for five years, no sanding no nothing its 14 bucks at kellymoore i think or benjamin moore! good luck