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Fitted some new rear rotors and pads two weeks ago and the non contact areas on the rotors are already rusting, not flash rusting embedded corriosion any idea how to prevent this?

paint them? take the rust off and tape the contact areas and paint the non contact areas. it might work im not 100% sure but try anyway if u do this DO NOT get paint on the areas of contact

I painted mine.
http://macen.nullnet.com/mods/brake_lines.php

most rotors are cast iron. Some are actually an alloy of steel & iron, but iron is a good choice for them because it absorbs heat better which makes for better dissipation. Iron exposed to the outside air, especially air that is humid will rust.

Rotors will rust immediately upon exposure to water. If you buy a new rotor, spray some water onto it w/a fine mist sprayer, it'll pop up 10 minutes later w/orange rust all over its surface.

This is why I painted my outside & inside of my rotor before putting my pads on. I sanded off the paint in the middle & popped them on & so far they haven't rusted on the outside or inside:

Gro Harlem wrote:most rotors are cast iron. Some are actually an alloy of steel & iron, but iron is a good choice for them because it absorbs heat better which makes for better dissipation. Iron exposed to the outside air, especially air that is humid will rust.

Rotors will rust immediately upon exposure to water. If you buy a new rotor, spray some water onto it w/a fine mist sprayer, it'll pop up 10 minutes later w/orange rust all over its surface.

QFT!