If your vehicle is showing excessive black brake dust accumulating on just one wheel, here are the most likely causes and the parts you'll need to fix each one.
The slide pins allow the brake caliper to float and release pressure. If they seize due to lack of lubrication or torn boots, the brake pads will constantly drag against the rotor.
Rust buildup under the hardware clips or failing to clean and lubricate the pad 'ears' during installation causes the pads to jam in the bracket, preventing them from retracting.
The hydraulic piston inside the caliper is stuck outward due to internal corrosion or a torn dust boot, applying constant heavy friction to that specific wheel.
The flexible rubber brake hose has degraded internally, acting like a one-way valve. It allows hydraulic pressure to apply the brakes but prevents the fluid from returning, keeping the brake engaged.
A severely worn wheel bearing allows the wheel hub and brake rotor to wobble as it spins. This constant knocking against the brake pads shaves off pad material rapidly.