Why buy new brake rotors instead of turning them?
Your mechanic has advised you to buy new rotors rather then having the old ones rotated, or "turned." Is he trying to rip you off? Can't we just use the old ones, or is it important to purchase new rotors when you put on new brake pads? There are a number of factors to consider before answering this question. But for the price of new rotors versus the price of having them turned - you might as well just replace them and give yourself some valuable peace of mind. With a cost difference of only about $10 per rotor, it may make a difference one day when you most need your maximum braking power.
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 recommened that you replace or turn your rotors before installing any new pads.
Your brake center can check the surface condition of your rotor with a straight edge to see if there is more then 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 is 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 over heated 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.
Brake rotors for front wheel drive vehicles are fairly inexpensive. Your rotors can be turned (rotated), machines 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 cost from $20-$30 per rotor and of course you will have a lot less problemsand a much longer rotor and brake pad life span.
During a brake service, you 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 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. Unfortunately, by turning every rotor that measures up, regardless of need, you lose preconditioned rotor surfaces.
Turning a "good" rotor makes it thinner and reduces its ability to absorb and dissipate heat. By turning this good rotor yo may cause warp in the near future when simply replacing the rotor assures you this problem will not occur.