Causes

• Tarnish is caused mainly by moisture that stays on the brake rotor, causing the rotor to discolor and eventually rust. When brake rotors are manufactured, they receive a light anti-corrosion film that prevents them from rusting before they are put to use during driving. This is removed when the rotors are installed. Because brake rotors are designed to be used continually, the metal of the brake rotor does not have a protective finish on it, since by nature it is constantly being "resurfaced" by the brake pads when the brakes are applied. This is why the rotors usually rust on old cars that have been sitting unused for years and years.
  
  

Removing Tarnish

• If your brakes are extensively tarnished from lack of use or other reasons, thoroughly cleaning them will most likely involve removing the wheels. Loosen the lug nuts and use a floor jack to raise the vehicle. Remove the wheels and set them aside. Spray the rotor and all of the brake components with brake cleaner. Let the cleaner soak onto the rotor for a few seconds and scrub the rotor with steel wool to remove the tarnish. You can also spin the rotor on the hub and hold the steel wool against it while it spins. After the tarnish is removed, spray more brake cleaner onto the rotor and wipe it down with a clean, dry rag. Wipe down the caliper and nearby components. Replace the wheels and lower the vehicle to the ground.
  
  

Preventing Tarnish

• The single most effective way to prevent tarnish is to drive the vehicle regularly so the brake pads can wipe off the rotors when the brakes are applied. If the vehicle is not driven very often because it is a collectible or second or even third vehicle, keeping it stored inside a dry garage or storage area is also recommended. If tarnish continues to build up, clean the rotors regularly.