Common causes of uneven brake pad wear include driving with warped rotors, a clogged brake line or leaky calipers. Vehicles that are heavier in the front than in the rear can wear brake pads unevenly due to an uneven distribution of weight. Debris in the breaking system, such as rocks or other foreign objects, wears brake pads down unevenly as well.
Most brake pads can be visually inspected to determine uneven wear. The absence of brake dust on wheels and rims can indicate that the pad is worn too thin and needs to be replaced immediately. Uneven amounts of brake dust are a good indicator of which brake pads need to be changed. A screeching or "metal on metal" sound can indicate that brake pads are worn out and must be replace to prevent further damage. Vibrations in the brake petal can also indicate brake pad wear, as can shuddering when depressing the brake petal.
According to the experts at How Stuff Works, when a driver brakes and feels the car pull to one side, it suggests a problem with the hydraulics and the brake system. If the unresolved problem persists, it can result in uneven wear on the brake pads.