What causes rotor warping (a.k.a. pulsating brakes)?

A. The term ?warped rotors? is commonly used to describe brake pulsation, but the rotor is not actually warping at high temperature so the term ?warped rotors? is not accurate. The primary cause of brake pulsation is from uneven friction deposits on the rotor. As the brakes get hot, friction material from the pad is deposited as a very thin layer on the rotor. If you come to a hot stop and clamp your brakes down, the pad continues to deposit material on one spot. As you continue to use the brakes, this high spot on the rotor will get hotter than other parts of the rotor. When the temperature starts to exceed 1150 F, the crystal lattice structure of the iron can change into a very hard, brittle material called cementite. Your brakes can hit 1100 F or higher coming off a highway ramp with severe deceleration. Hard spots start to form, and it doesn?t wear down like the rest of the rotor. The hot spot nodules will not dissipate heat as well as the neighboring material, so it gets hotter ...  more