You've probably heard ads for free brake inspections, and you may be wondering what the companies check for and how to know if you're being sold the correct services once they make a diagnosis.
Here's a primer on brakes so you can make an informed decision.
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. 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 it causes a sinking brake pedal.
Brake rotors are dinner-plate-size 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.
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. 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 would include 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 three 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.