Brake pads
Definition
Brake pads are steel backing plates bonded to a friction compound that is pressed against the disc; the compound is formulated as organic (NAO), low-metallic, semi-metallic or ceramic to balance bite, fade resistance, dust, noise and disc wear. New pads are typically 10-12 mm thick and should be replaced at about 3 mm of friction material, or sooner if the wear indicator (a steel tab that squeals, or an electrical sensor) is reached; always inspect both inner and outer pads since the inner one often wears faster. Uneven wear between pads points to sticking slide pins or a piston, tapered wear to a worn carrier or caliper, glazing and cracks to overheating, and a smooth shiny surface with poor braking to contamination from grease or leaking fluid. Fitting procedure matters: clean the carrier contact points, fit new shims and hardware, lubricate only the correct contact points with high-temperature brake grease, seat the pads with several moderate stops from 50-60 km/h and avoid hard braking for the first 200 km. Related codes: pad wear sensor circuit codes on cars so equipped (e.g. VAG 01044, BMW 5F3F) and no generic P-codes; related symptoms are squeal, grinding when down to metal, long pedal and pulling.