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Hendon Publishing

Preventing Warped Rotors

Brake rotors can warp as a result of heat from frequent, heavy braking. You know, the extremely aggressive traffic officer who leads the department in DUI arrests, goes through three books of citations a week, and averages 7 mpg on patrol. You know, the guy who gets 5,000 miles on a pair of front pads, 5,000 miles on a set of four tires, and needs a new transmission every 30,000 miles.

However, what causes warped rotors on patrol cars that are not driven so hard? In fact, some easily driven patrol and admin cars seem to get warped rotors just as fast as those on the car driven by the Traffic Officer of the Year. Why?

The answer is irregular wear on the rotor from occasional contact with the semi-metallic brake pads. These rotors aren’t really warped. Instead, they are worn or abraded off-center by intermittent contact with the brake pads.

On a disc brake car, once the brake pedal pressure is relieved, the brake pads are only pushed away from the rotor and back into the caliper by the flex in the rotor on the wheel bearings. On the average driven car, and certainly on the aggressively driven car, the rotor flex quickly and firmly pushes the pads away from the rotor once the brake pedal is released.

On a more easily driven car, the rotor does not completely push the brake pad back into the caliper. The rotor and the brake pad are just slightly apart, just barely not in contact. Going down the road, the rotor moves slightly back and forth on the wheel bearings. In doing so, the rotor also intermittently touches the nearby brake pad. Semi-metallic brake pads are, of course, highly abrasive. Over time, the pad wears the rotor in an uneven manner.

When the brakes are applied, the unevenly worn rotor on the easily driven car produces the same vibration during pedal pressure as the heat-warped rotor on the aggressively driven car. The diagnosis is the same. The solution to the problem is the same, i.e., turning the rotors solves the vibration problem. Then, of course, the same intermittent wear situation starts all over again.

The real solution? Use less aggressive, less abrasive “retail” brake pads on these more easily driven cars. The retail pads may be Non Asbestos Organic (NAO) or they may be semi-metallic pads with lower amounts of metallic fibers (low-met pads). Either way, these retail pads are less abrasive and are less likely to erode the rotor from the frequent and intermittent contact.

Of course, the retail pads will not produce the same braking performance under pursuit conditions as police package pads. However, these easily driven cars rarely see that kind of duty. And all OEM retail pads meet federal FMVSS standards, so use the OEM pads for the retail Impala.

These OEM retail pads may be a maintenance solution for the car with “warped” rotors driven by an officer who swears he is easy on the car. He actually may be too easy on it!

Earl Gautsche is the National Police Fleet Service Manager for GM fleet. He can be reached at (248) 789-4679.

Published in Police Fleet Manager, Mar/Apr 2006

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