Bad rotors

kiddiccarus said:

Screw Turning Rotors. I charge you $40 per rotor to turn them. Buy New Rotors!!!

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I'm the other way. I prefer sending my customer out the door with machined OEM rotors rather than aftermarket new. New OEM is best, but when cost is a concern, I'll take machined OEM all damned day over the Chinese from a parts store. (Of course, I have a ProCut on-car lathe at work, I can get them perfect every time.)

There's a lot of misinformation in this thread. I'm going to tackle some of that.

The majority of the time, the rotor itself isn't warped (there are times when they are, I'll get to that in a second). What is usually happening is a buildup of brake pad material on the rotors causing the pulsation. If you feel the pulsation in the steering wheel, it's usually the front rotors, if you feel it coming up through the seat, it's usually the rears. Machining the rotors removes the buildup and provides a uniform surface for the pads to grip. The problem is more prevalent than ever with modern semi-metallic, non-asbestos organic, and ceramic pads (the old asbestos-based pads were nowhere near as bad about it, but they had their own issues). A correctly machined rotor (cut as few passes as possible, cut evenly on both sides without cutting overly deep, with the machine setup properly so it doesn't chatter or squeal, and not cutting the rotor below minimum thickness spec) will perform as well as a new rotor for nearly as long. The second most common cause is rust buildup on cars driven through the snow in the salt belt. This is especially a problem on non-vented rear rotors on Nissans for some reason.

As far as when a rotor is actually warped, that happens a few different ways:

1. Some idiot really overtorques the lug nuts or wheel bolts, causing the rotor to deflect. Throw a few heat cycles on that and the problem is permanent, and machining won't fix it because the rotor will be imbalanced even after machining.

2. The rotors get cooled too quickly after being heated up from heavy stop-and-go traffic or a long deceleration off a highway. This happens a lot when someone goes straight to a car wash or drives through a puddle immediately after getting the rotors good and hot. This usually only warps the rotor slightly and at the surface layer, machining can fix this.

3. The brakes are abused, causing the rotors to overheat. If your rotors are blue, you're beating on them too hard. Machining may help, but rotors that have been heat-cycled to that extent are prone to having "hard spots" in the metal beneath the surface, meaning the problem will return.