Quote:
Originally Posted by Fountainhead
I'm kind of on the fence about warp, I just know that in the old days, when all the auto parts houses would turn the rotor, when we clamped the rotor to the lathe and just rotated the rotor against the lathe bit there would indeed be an uneven surface. Thinking back none of us questioned the "trueness" of the lathe, the trueness of the rotor mounting face, we just turned the rotor until the high spots were gone and put it back on the car and the problem was solved. Usually we saw rotors that were ran several years on the metal face of the worn out pad by drivers that had no idea what the noise was but they KNEW it would cost them money so they just kept on going, haha.
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The pulsation and loss of braking power is definitely caused by high spots on the friction surface, but that's not necessarily caused by warpage.
You would have to measure both sides of the rotor's change in position relative to the mounting hub in real time. If one side sticks out 2mm and the other is recessed 2mm at the same spot, then chances are the rotor is warped. If both sides stick out, or only one side sticks out, chances are it's cementite formation causing the hardness of the rotor material to increase so that it wears at a different rate than the surrounding metal. This causes the condition to gradually worsen over a period of time, making it "sneak up" on the driver in most cases.
Truly warped rotors are usually obvious almost immediately and don't "sneak up" on the driver. One minute they're fine, the next minute there's a pronounced pulsation in the pedal.