Vehicle pulls to one side. Is your car pulling or steering to one side or the other when you are driving? Inside the brake caliper, one or more pistons move in and out in response to hydraulic pressure from the master cylinder (pump) when you press the brake pedal. If the piston(s) in one of the front wheel brake calipers freezes up because of dirt, debris, or corrosion, the brake pads will either fail to come in contact with the rotor or they will fail to release the rotor. In the first case, the vehicle will pull away from the damaged side during braking. In the second case, the vehicle will pull toward the damaged side — when the brakes are applied (and sometimes when they are not).
Squealing or metallic rubbing noise. If a brake caliper is sticking or freezing up, noises may be heard from the area of the damaged part. Unlike the noises related to worn brake pads (which occur when the brake pedal is pressed), this symptom is likely to be heard when the brakes are not being used. If let go for too long, the brakes could lock up completely and prevent that wheel from turning.
Uneven brake pad wear. If a caliper is bad, chances are that the brake pads will wear unevenly. If you notice that the brake pads have worn thinner on one side of the vehicle than the other, the caliper is likely at fault. A technician inspecting your vehicle or performing other repairs may also notice this symptom.
Leaking brake fluid. Because a brake caliper functions as the result of hydraulic pressure, any weak spots in the system can leak hydraulic oil (brake fluid). A wet, oily spot on the ground inside the tire can be an indication of a leaky caliper.
Clunking sound. In rare cases, a caliper bracket that holds the caliper in place could break and cause a loud clunking sound. The brakes may lock up at that wheel and significant is possible. The vehicle should not be driven if this happens.