Excessive lateral runout in a brake rotor may cause a few unwanted driving sensations. Most common is a pulsation or ‘shimmy’ when braking at higher speeds. Although the expression ‘warped rotors’ is still prevalent when talking about brake pulsation issues, the real culprit of brake roughness isn’t always rotor warping, but rotor-thickness variation. Even rotor thickness variations as little as 0.0008″ can generate noticeable symptoms. Another sensation is ‘judder’ or roughness. This condition can be experienced both cold and warm. Cold roughness develops under normal driving conditions (low brake temperatures), and manifests as pedal pulsation and sometimes steering wheel shaking. Warm roughness occurs with higher-energy braking events generating temperatures in excess of 700 deg F. Localized thermal expansion of the rotor develops into uneven wear of the rotor but also leads to speed related variations in friction force.

Pulsation can result from a brake job completed with the installation of new pads and rotors if the mating surface between the brake rotor hat and hub face is not completely free of rust and scale buildup. A technician installing new brake rotors should always allow time to clean and resurface the hub face and around the wheel studs.

If part of the the rotor surface does not appear shiny, where the brake pad and rotor are to make contact when the brakes are applied, a problem with one or more brake system components is likely. Sometimes this condition can indicate an issue with the fitment of the brake pads into the brake caliper bracket or a seized caliper slide pin. Other times it can be a hydraulic issue or a failed brake caliper. A proper brake inspection, by an experienced mechanic, should be performed prior to replacing any components or opening hydraulic lines. Please CONTACT US and we will be happy to schedule you for a brake system inspection.

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