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Originally Posted by DZeckhausen
Proper bedding will usually eliminate this unless the judder problem has gone unchecked for a while. The transition between bedded and unbedded portions of the rotor result in local hot spots that tend to accumulate more pad material and can eventually change the molecular structure of the rotor, resulting in cementite deposits. These deposits can't even be removed by turning, since the lathe's blade tends to skip over these hardened spots. When the problem has become this bad, rotor replacement is the solution of choice.
However, proactive bedding whenever you purchase a new car or install new rotors, should "inoculate" you from judder problems caused by transfer layer thickness variation.
Keep in mind that there are other root causes of judder that can be initiated by application of the brake pedal, but aren't directly caused by a brake problem. For example, the combination of old, weak shocks with worn control arm bushings and/or ball joints combined with a slight imbalance in the wheel/tire assembly can lead to a transient judder problem at certain speeds that is often triggered by a sharp input to the brakes. Diagnosis is often wrong, since attention naturally falls to the brakes as the culprit. Instead, it's the rhythmic input to a system (the car's suspension) that has a natural fundamental frequency. When the rhythmic input is a multiple (harmonic) of the suspension's fundamental frequency and the shocks are too weak to damp out oscillations, the "kick" from a sudden brake input may be enough to start an oscillation that continues until the vehicle speed falls outside a range of speeds. So, speeding up or slowing down may make the judder go away. And it's not necessarily the fault of the brakes. Most of the cars on this forum are too young for this to be happening yet.
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So, if I am turning my rotors and on the first cut, parts of the rotor are being cut and parts of the rotor (as in whole sections) are being completely skipped over, this is not a warped rotor?
My Q45: 154 mph, heavy car, stock brakes, had "Warped Rotors" on several occasions (also boiled the brake fluid numerous times). Each time I cut the rotors (until they got too thin, then new rotor time) whole sections were skipped over on the first cut.
The reason I ask is the article from stop tech you linked says that the author has never seen warped rotors, it's always a misdiagnosis!
Not arguing, just want to learn.
Dan