[Jakey]

Originally Posted by CRAIG

I am not saying that it is the only reason but it is a contributing factor. Here is why:

Regardless of pad composition, if both disc and pad are not properly broken in, material transfer between the two materials can take place in a random fashion resulting is uneven deposits and vibration under braking. Similarly, even if the brakes are properly broken in and when they are very hot or following a single long stop from high speed or if the brakes are kept applied after the vehicle comes to a complete stop it is possible to leave a unique deposit behind that looks like the outline of a pad. This kind of deposit is called pad imprinting and looks like the pad was inked for printing like a stamp and then set on the disc face.

Cast iron is an alloy of iron and silicon in solution interspersed with particles of carbon. At elevated temperatures, inclusions of carbides begin to form in the matrix. In the case of the brake rotor, any uneven deposits standing on top of the disc surface become hotter than the surrounding metal. Every time that the leading edge of one of the deposits rotates into contact with the pad the temperature increases. When this temperature reaches around 1200 or 1300 degrees farenheit the cast iron under the deposit begins to transform into cementite (an iron carbide in which three atoms of iron combine with one atom of carbon). Cementite is very hard, very abrasive and is a poor heat sink. If severe use continues the system will enter a self-defeating spiral the amount and depth of the cementite increases with increasing temperature and so does the brake roughness.

But I would say all of this is a direct reflection of the rotating assmebly being out of balance, combine that with a hard driving style, long stops from high speeds and you will have obvious problems. The choice of brake pads and rotors you chose will also affect how quickly they reach the failing temperature I stated above.

Again this is just my opinion, take from it what you want.

CRAIG

Do you have the source for your middle paragraph?