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October 7, 2012

A primer on brakes

(Continued)

Brake rotors are dinner-plate-sized metal discs located just behind your wheels. They may last the life of the vehicle, but can wear thin, become warped from brake overuse, or become damaged by worn-through pads. If a car or truck stops smoothly, with no pedal pulsation or squeaking, the rotors are probably OK, although they should be checked for adequate thickness. Rotors that have worn too thin don’t dissipate heat properly, and must be replaced. I’m not a fan of machining rotors unless called for by noticeable symptoms.

Rear drum brakes contain a wheel cylinder, brake shoes, springs and shoe-holding hardware, and the brake drum. Typically, the brake shoes should be renewed when the friction material wears thin. You might also need to machine the drums, which restores roundness and surface finish, and renew hardware and possibly the wheel cylinder, if it’s leaking. I’d avoid machining the drums if the vehicle slows smoothly with the parking brake applied. Wheel cylinders and hardware often last the life of the vehicle.

The definition of a brake inspection can vary widely, and a free one may be accompanied by higher-than-normal sales pressure. Typically it may be a visual inspection of the above parts, a measurement of rotor or drum thickness, a check for an illuminated ABS light or codes, and a road test. Fluid may also be tested for contamination with a test strip.

Most vehicles will require only brake pads or shoes and fluid renewal (recommended) during a brake job, with perhaps 3 out of 10 needing rotor surfacing or replacement. Other parts are rarely needed; get a second opinion if they are pushed.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at under-the-hood@earthlink.net; he cannot make personal replies

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