Twenty-something years ago, there was a long and involved article making it's way around the Internet. Had to do with the "myth" of warped rotors, and how the real problem was pad material building-up on the rotor surface. "Rotors don't warp, they get contaminated with pad material".
Having cut hundreds of rotors, many of them due to customer complaints about pulsating brakes, and watching the cutter bit carve the high spots off the rotors, I never believed the story about pad material transferring to the rotor in any meaningful way. Certainly not enough to create high spots.
Trailblazer rotor, light silver is fresh metal as cut by brake lathe. Dark metal is worn metal from pad friction, rust pitting, and warpage. The dark metal parts are "low spots". Each successive cut reduces the amount of dark metal/low spots until the entire rotor surface is cut down to the level of the low spots. At that point, the rotor must be measured to assure it's still within service spec for thickness. It's entirely possible to cut the rotor so much that there isn't enough metal left for safety and heat absorption.
My brake lathe is nearly as old as I am. It is not capable of providing a beautifully-smooth surface finish like you'd see with new rotors--or newer brake lathes. Even so, it's better than nothing. The Trailblazer rotors have six-ish months on them and working perfectly.
IF there's a rotor fault, I say it's either Runout, or Thickness Variation. Thickness variation is unlikely with a new rotor, entirely possible with a used rotor. Runout is a possibility with a rotor of any age including new-in-the-box; because we all know who took a giant, steaming-hot dump in the Replacement Brake Rotor Well.
Checking for runout on a new K2500 rotor "riveted" to a 180K hub via the lug-studs. (Result was approx. .001 Total Indicated Runout (TIR))
Having cut hundreds of rotors, many of them due to customer complaints about pulsating brakes, and watching the cutter bit carve the high spots off the rotors, I never believed the story about pad material transferring to the rotor in any meaningful way. Certainly not enough to create high spots.
Trailblazer rotor, light silver is fresh metal as cut by brake lathe. Dark metal is worn metal from pad friction, rust pitting, and warpage. The dark metal parts are "low spots". Each successive cut reduces the amount of dark metal/low spots until the entire rotor surface is cut down to the level of the low spots. At that point, the rotor must be measured to assure it's still within service spec for thickness. It's entirely possible to cut the rotor so much that there isn't enough metal left for safety and heat absorption.
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My brake lathe is nearly as old as I am. It is not capable of providing a beautifully-smooth surface finish like you'd see with new rotors--or newer brake lathes. Even so, it's better than nothing. The Trailblazer rotors have six-ish months on them and working perfectly.
IF there's a rotor fault, I say it's either Runout, or Thickness Variation. Thickness variation is unlikely with a new rotor, entirely possible with a used rotor. Runout is a possibility with a rotor of any age including new-in-the-box; because we all know who took a giant, steaming-hot dump in the Replacement Brake Rotor Well.
Checking for runout on a new K2500 rotor "riveted" to a 180K hub via the lug-studs. (Result was approx. .001 Total Indicated Runout (TIR))
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