Is there a way to anticipate when one needs to have the brakes replaced on your car? I’ve heard some cars will make a squealing noise, while others seem to squeal randomly. Is there a reduction in braking ability? What damage or consequences occur if one goes farther than they should before replacing brakes? How long can one expect brakes to last? The reason I ask is the place I bought my tires rotates them regularly, but doesn’t check the brakes, since they do just tires. Same with my oil change place – I don’t think they know what brakes are.

– Amanda Saldon, Sunnyvale, Calif.



Wow! So many good questions! It’s difficult to anticipate the life remaining in a set of brake pads unless they are equipped with a wear sensor. Some vehicle manufacturers (and replacement parts suppliers) attach a small metal tab to the brake pad. As the pad’s friction material (lining) wears down to about 25 percent of the original thickness, the tab begins to rub against the brake rotor, causing an annoying squeal.

Oddly, the squeal – sometimes a cycling or continuous shrill sound – is typically heard when you are not depressing the brakes, and diminishes or changes as the brakes are applied. Hopefully, this is not to be confused with typical brake squeal, caused by vibrating brake pads and/or a glazed pad or rotor finish. This sound may be intermittent and occurs only as the brakes are applied. Some vehicle manufacturers also embed an electrical contact and wire within the brake pad. As the lining wears thin, the contact grounds to the brake rotor, illuminating a warning lamp.

In most cases, brakes function well right up to the point of metal-to-metal contact. This condition occurs when the brake pad’s lining is worn such that the metal pad itself begins contacting the brake rotor. Often accompanied by a growling sound, this is big trouble, as braking performance is compromised and the brake rotor will become irreparably damaged.

For this reason, periodic brake inspections are needed, preferably every 10,000 to 15,000 miles. Most brake calipers allow at least one corner of an inner and outer brake pad to be viewed, and the lining thickness noted. This might be possible to do with a small swivel-head mirror, through the wheel spokes, or might require wheel removal. A new pad’s lining will be about the thickness of four or five quarters. If the lining appears to be two quarters or less in thickness, replacement is needed. In some cases one pad wears more rapidly than the other, or at a taper, so we need to be conservative when viewing just one pad or the pad corners.

How long can one expect brakes to last? This is a real wild card, as some drivers and vehicles are tougher on brakes than others. Front brakes typically last between 30,000 and 60,000 miles and the rear brakes perhaps 40,00 to 70,000 miles. I’m not a fan of indiscriminate rotor turning (surface machining) at the time of pad replacement unless pulsation, vibration or noise symptoms are evident. I’d like the rotors to remain as thick as possible to dissipate heat and resist warping.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose.