How long before turning brake rotors?

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Well, I've never seen a brake lathe that would cut that much without breaking. I've never taken my rotors to anyone I don't trust. 98,000 miles and she stops straight and true, no vibration, no complaints and the rotors have a ton of life left to 'em. Hey, do what you want, just relating my personal experience, as is everyone else here.

 

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On my 96 4x4 the lateral runout spec on the disc is 0. 005". My rotors turned off the truck on a brake lathe were at 0. 020 and 0. 025". I watched as they were mounted several times on the lathe and they seated reliably with about 0. 0025" each time i made the brake guys mount them (second trip to the shop after they made my brake problems worse). They also spun true on the lathe. But the "truck axis" is not the "lathe axis". I had a Chevy dealer turn them on the truck and the lateral runout was about 0. 0005" (notice the extra zero) I went from 5 times the spec too less 1/10 of the spec and guess what my brakes worked great.

I would never ever turn your rotors unless they measure over 0. 005" WHILE ON THE TRUCK, are burned, grooved, or visibly damaged. Always turn them on the truck or you lose.