Good luck getting agreement on this issue. From what I've read, not only is it questionable to resurface today's rotors, but it takes a great technician and excellent equipment to get a quality resurface job. I know GM issued a TSB advising against routine rotor resurfacing as part of a brake job. Seems like scuff sanding for a non-directional surface followed by a detergent wash would be a good idea if you choose not to resurface. Here's a good excerpt from this web page:
http://www.americasprideonline.com/brake-lathes/brake-service-articles.shtml
To cut or not to cut
By now it should be easy to determine if the rotor requires replacement or if resurfacing is necessary to bring the rotor within specifications. But what if all measurements were within specification, the friction surface is smooth and the vehicle had no brake problems other than worn linings? Should the rotor still be resurfaced? Unlike the old days, today the prevailing wisdom is "no" for several reasons.
Resurfacing the rotor unnecessarily removes material and makes the rotor thinner, lessening its ability to absorb and dissipate heat and shortening the rotor's useable lifespan. Improper machining also can create problems. For instance, if a non-integral rotor is not setup properly on a bench lathe, an excessive lateral runout condition that did not previously exist can be created when it is reinstalled on the hub. Improper resurfacing also can create a friction surface that is too rough, causing brake noise, premature pad wear and a hard pedal condition.
Many of the OEMs have issued bulletins in the last few years providing guidelines for brake rotor servicing. In these bulletins, they've indicated that brake rotors should not be resurfaced during routine brake pad replacement. Most also recommend that new rotors not be resurfaced.
Finally, if the rotor's surface condition is acceptable and all dimensions except runout were within specification, the technician should try changing the position of the rotor on the hub and rechecking the runout. A change in position may bring runout within allowances.
If inspection and measurement determined that resurfacing is necessary, there are two alternatives: the traditional bench lathe or an on-car brake lathe. As stated previously, a traditional bench lathe is fine for resurfacing rotors with integral hubs and tapered roller bearings. However, a bench lathe requires more effort for turning non-integral rotors or excessive lateral runout can be created. After measuring runout with the rotor on the hub, the runout also must be measured with the dial indicator when the rotor is mounted on the lathe. If the runout isn't in the same place and/or the same amount, the rotor should be shimmed until the runout is duplicated.
Another way to use a bench lathe and maintain lateral runout within specifications is to use tapered shims. After the rotor is resurfaced, it is remounted on the hub, and runout is checked with a dial indicator. If runout is excessive, the high spot is marked and the rotor is removed. The tapered shim is then installed on the hub with the thickest part opposite the high spot. When the rotor is reinstalled, runout should be within specification.
When using a bench lathe to resurface composite rotors, special adapters must be used to support the steel center section, or the rotor can flex and cause runout and surface finish problems. Also, if an aftermarket cast replacement rotor is used to replace a composite rotor, the rotors on both sides of the vehicle should be replaced, regardless of the other rotor's condition.
For a bench lathe with a fixed 150-rpm spindle speed, a rough cut of 0.005 inches can be made at 0.006 to 0.010 inches cross feed per revolution. A finish cut of 0.002 inches should be made at no more than 0.002 inches cross feed per revolution.
On-car brake lathes fall into two categories--caliper-mounted lathes and hub-mounted lathes. Both types are ideal for resurfacing rotors on vehicles where the rotor is difficult to remove.
Caliper-mounted lathes were the first type of on-car lathes widely available. They are two-piece units with one part rotating the rotor and the other part being the cutting mechanism, which is attached to the steering knuckle. They usually require many adapters due to the variety of steering knuckle designs, and they can be time-consuming to set up.
Hub-mounted lathes combine the rotor drive device and cutting mechanism in a single unit. These lathes machine the rotor so that it is perpendicular to the wheel's axis of rotation, thereby minimizing runout. Most require only five or six adapters to allow hub attachment on most cars and light trucks. The latest design hub-mounted lathes can resurface a rotor in approximately 10 minutes, from the time the machine is attached, to the finished rotor. Some offer automatic runout compensation, which further simplifies the setup process.
Regardless of the type of lathe that is used, the finished surface of the rotor must be very smooth: between 20 and 70 micro-inches. After the rotor has been machined, the friction surface should be sanded with 120- to 150-grit sandpaper, mounted on a sanding block, while the rotor turns on the lathe. A non-directional finish should be applied using the sandpaper, until the machined finish that was created by the cutting bit begins to disappear, about one minute per side.
