To purchase new brake rotors or turn them, ah that is the question. You are wasting your money if you are fitting new brake pads on your vehicle and your rotors are seriously scored or hollowed. It’s extremely dangerous and could also cause the vehicle a total loss of brake. No one ever wants to experience total brake loss. Therefore it is strongly recommended that you replace or turn your rotors before installing any new brake pads.
Your brake center can check the surface condition of your rotor with a straight edge to see if there is more than 0.5mm or 0.020 inches of hollow and if so your rotors must be turned or replaced. If you do not turn or replace the rotors you will have a dangerous braking situation and your pads will become damaged. Since this a safety issue of the utmost importance, it is strongly recommended that you have a professional mechanic take this measurement for you. Rotors can be turned only about 1 or 2 millimeters before they become too thin for safe use and will have to be discarded and replaced.
Brake rotors that have been repeatedly overheated may warp and create a vibration in the wheel. This warping will significantly wear out your tires and suspension systems. If you press the brake pedal successively harder while coming to a stop and you feel a pulsing sensation, the rotors are more than likely warped. A mechanic can take multiple measurements around the rotor with a micrometer to determine how much variation or warping is present.
Disc brake rotors for front wheel drive vehicles are fairly inexpensive. Your rotors can be turned (rotated), machined and still be within factory guidelines, but this usually leaves them thin whereby leaving them to warp or vibrate.
The cost for turning a rotor runs anywhere from $15 to $25 per rotor. Purchasing new rotors typically will only cost from $20-$30 per rotor and of course you will have a lot less problems and a much longer rotor and brake pad life span.
During a brake service, your technician needs to verify that each rotor is not warped and meets the legal minimum thickness specification. Every rotor that falls within these specifications is turned on a lathe and then sanded on both sides for a smooth, non-directional finish. This is the correct way to “turn” rotors that need to be machined, and it provides a smooth surface for the new pads. Unfortunatley, by turning every rotor that measures up, regardless of need, you lose preconditioned rotor surfaces.
Turning a “good” brake disc makes it thinner and reduces its ability to absorb and dissipate heat. By turning this good rotor you may cause warp in the near future when simply replacing the rotor assures you this problem will not occur.