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We recently brought our 2015 Hyundai Tucson to the garage to have our summer tires put back on. During the process, we were informed that we needed to have new brakes for all four wheels. My husband was told that one of the rear calipers had seized, and that the front pads were also seized and worn. I don’t understand how our car could brake OK when most of its brakes were seized. Did we get lied to? Why did they insist on replacing both rear calipers instead of just the bad one?

Tire-changing seasons, both in the spring and fall, are also busy times for brake work. Removing the wheels exposes the brakes, making it easy to inspect them. And like in a Cracker Jack box, there can be a surprise inside.

Brake corrosion is common. The wear surfaces of disc brake rotors and their components are exposed to the air and elements, even if they’re partially protected by the wheels and vehicle body. It’s not just from driving in wet conditions, either. The same moisture in the air that causes condensation or frost on your vehicle’s windows has a similar effect on the metal brake parts. Even for those parking indoors, the corrosive effects of winter’s road salt and brine come into play.

Normally, if all else is good, regular use from driving will tend to quickly scrub this fine layer of corrosion off the wear surfaces. But if the rust is allowed to get a bit deeper into the rotor surface, the opposite occurs. The swollen or pitted metal wears the pad material down, compounding the problem and possibly causing brake pulsation or noise. Working from home, and other pandemic-related driving reductions, appear to have made this issue more prevalent.

Even partially seized brakes can continue to function to a degree. With power assist and hydraulic brakes, the pressures generated at the calipers can potentially bend the brake-pad backing plates and caliper pins enough to apply some force. Under light to moderate braking, you might not notice the performance loss. (Once applied, the stuck pads may not fully release and could drag; uneven or grossly premature pad wear results.)

As to why calipers are replaced in pairs, this is standard industry practice. Ostensibly this preserves hydraulic system balance. And, like changing both wiper blades when one starts to smear, it also reduces the probability that the other caliper, having experienced the same service life, may also soon fail and damage the newer brake parts.

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