Brake dust is a common and not worrisome by-product of the brake pads in a modern car wearing down over time. Some cars are much worse than others. In fact, many cars have no detectable brake dust on their rims, but others have a lot. If you notice that just one of the rims on your car are being coated in brake dust, it could mean that the brake caliper is not doing its job properly. It is something you should not ignore.

Modern brakes, particularly up front, use rotors and calipers. The rotors are the metal disks you can see if you look through the spokes in the wheels. The calipers are the things that clamp around them. The Calipers are affixed to the car, and they pinch the rotor when you step on the brake. They are helped along courtesy of a hydraulic piston. To keep the expensive parts from wearing out (in theory), the calipers have a sacrificial pad on each side of the rotor that makes the contact.

When you see a lot of brake dust on just one side, it can mean that the caliper is acting up. The general term for this is “frozen caliper.” It means that the caliper is able to pinch but not let go when you stop pushing the brake pedal. The result, and the clue, of trouble is the brake dust you see on just that wheel.

Calipers can also freeze open, meaning they don’t pinch enough, or at all. One symptom of that is the car pulling to one side gently or abruptly when you brake hard. Another is if the car seems to add a lot of braking force unexpectedly when you have a near-panic stop situation.

The cure is almost always a new caliper. Although a caliper can be freed up in theory, it is generally not worth the time to do so. Worse, if one is frozen and has reduced the thickness of the rotor, you may need that part as well. Then there is the thinking that if you are going to do one side, it makes sense to do the other. Brake dust is expensive it turns out.

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