New Rotor Bedding-in Procedure:
All new iron and steel rotors should be bedded in before being used under racing conditions. Proper bedding in will prolong the rotors life and make it more resistant to thermal checking or cracking under severe braking conditions. The following procedures should always be followed when bedding in rotors:
Thoroughly inspect all brake system components before proceeding to track.
Check all bolt connections. Make sure mounting bolts and rotor bolts are properly lockwired, that brake pads are properly secured by retaining clips or cotter pins, that master cylinders and brake pedals are working properly, that brakes are properly bled with plenty of fluid, and that proper engagement of brakes occur when pedal is depressed.
Always bed-in a new rotor (disc) using a used set of pads, preferably ones which will not create heat rapidly. Generating heat too quickly will thermal shock the rotors. Likewise, when bedding-in a new set of brake pads, use a used rotor.
Make sure that the rotor surfaces are free from oils, grease, and brake fluid.
Close air ducts approximately 75% to expedite the bedding-in process.
Run vehicle up to moderate speed and make several medium deceleration stops to heat up the rotor slowly, this will help reduce the chance of thermal shock.
Accelerate vehicle to a high speed and apply the brakes bringing the racecar down to a slow speed, repeat this process until the rotors reach approximately 1000 degrees F. Do not apply brakes during acceleration.
Pull into the pits and allow the rotor to cool to ambient air temperature.
Do not hold brakes on after performing the bedding-in procedure until cooling is completed.
Do not sand rotors or pads after bedding-in. Any shutter or pulsation will most likely go away after several repeated hard stops.
Rotors are blanchard ground to ensure the rotor surfaces are flat and parallel. Sometimes hubs, bearings or other components have runout that causes the rotor to runout. Allowable runout is .005 - .008. Adjust the runout by placing shims between the rotor and hub, or hat. Runout should be rechecked every week. You can assume the runout to be acceptable as long as you are not experiencing brake drag, pedal oscillation, or piston knock back.
Rotors will eventually start to show signs of wear how fast depends on the type of racing, the frequency, and the brake usage. Grooving and/or cracking due to severe heat and thermal cycling indicate the rotor should be replaced. Note that surface checking itself is not a sign a rotor needs replacing as this can occur on iron rotors. Always replace rotor mounting bolts and lockwire whenever replacing rotors, taking care to inspect mounting hats or hubs for signs of abuse.