EagleTribune.com, North Andover, MA


October 7, 2012

A primer on brakes

I keep hearing this advertisement on the radio about a place offering a free brake inspection. Can you please explain what they’d check on my brakes and how I’d know that I’m being sold the correct things? I don’t know anything about brakes, so let’s keep it simple.

No problem! Your car, unless it’s a classic, has disc brakes in the front, and either drum or disc brakes in the rear.

Disc brakes use a clamping device called a caliper to press brake pads against the brake rotor. There is an inner and outer pad, and they contain friction material on the side pressing against the rotor.

Disc pads somewhat resemble an elongated, double-stuffed Oreo cookie, with one outer piece removed. The filling is the friction material, and the cookie part is the metal backing. Pads must be renewed when the friction material wears thin, or the metal backing will damage the rotor’s smooth surface.

Brake pads may last 25,000-75,000 miles, depending on driving habits, vehicle type and friction material composition. Pads that stop the best typically create more dust and don’t last very long, and long-lasting pads are often noisy and don’t stop as well. Try for the middle.

Calipers are operated by hydraulic force, via brake fluid, which is sent under very high pressure from the master cylinder as you apply the brake pedal. Calipers rarely leak or bind as long as the brake fluid is renewed every four or five years. The master cylinder, located in the upper-left-rear corner of the engine compartment, utilizes a fluid reservoir, which needs to be checked periodically for proper fill level. In the very rare case of master cylinder problems/leakage, it’s usually internal, and causes a sinking brake pedal.

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