The Disc Brake Rotors are a main component of your vehicles Braking System. The Rotors are a wearying item, and should be schedule checked to assure proper condition before a problems may arise.

Rotors are found on all different types of road and off road vehicles. Brake rotors can be found on bicycles, motorcycles, cars, trucks, trains and airplanes. Rotors are constructed of many different materials, most commonly made of cast iron. Cast iron is preferred because it absorbs and dissipated heat well, resists ware and is inexpensive compared to other metals.

Function

When you push on the brake pedal the caliper squeezes the brake pads against the rotors. A small amount of brake pad friction material is transferred from the pads to the rotors; helping the rotor and pads to stick providing friction. The friction created converts Kinetic Energy to Heat Energy. The Rotors dissipation of this heat is what causes the vehicle to slow down and Stop. The material transfer is why it is important to break in the pads and rotors. If the pads are not properly broken in, they may leave an uneven deposit of friction material on the rotor surface resulting in a high runout, Disc Thickness Variation or other problems.

Brake Rotor Problems

Rotor Runout: A measure to determining whether the rotor axis is parallel to the spindle axes. If the runout is too high it will result in a high and low point on the rotor contacting the brake pads causing pulsation in the brake pedal under braking. The runout can also occur if the rotor is unevenly warn and is thicker and thinner in different locations on the brake contact surface called Disc Thickness Variation (DTV).

Note: It is important to check runout when doing a brake job, especially when installing new rotors.

Runout tolerance: Tolerances can vary for different vehicle. Some vehicles are more sensitive to runout than others. Commonly lighter vehicles with lighter suspension are more sensitive and require smaller runout. Also a warn brake, suspension and steering components will also amplified the vibration form the rotor runout. To measure runout a dial indicator is needed. The dial is placed on the face of the rotor, the rotors is turned slowly while reading the dial. If the runout exceeds factory specification it will need to be correcting to avoid vibrations.

Note: When installing new rotors in many cases runout can be corrected by removing the rotor and repositioning it on the hub, make sure that the rotor and hub mounting surfaces are clean, clean, clean. If repositioning the rotor dose not reduces the runout, it can be corrected by placing shims in between the rotor and the hub. Shims of different thicknesses are available to correct the runout.

Runout can occur due to: