A sticking caliper is one of the most common brake failures, and it comes down to a few specific causes. Knowing them helps you fix and prevent it. Here is why brake calipers stick.
Seized guide pins
Floating calipers slide on two guide pins. When the grease dries out or the pins corrode, they seize, and the caliper cannot center itself - so it drags; see caliper slide pins. This is the single most common cause and the easiest to prevent with fresh grease.
A stuck piston
Rust or corrosion in the caliper bore, or a torn dust boot letting grit in, can seize the piston so it will not retract; see sticking caliper. Old, moisture-laden brake fluid speeds this up by corroding the bore from the inside.
A collapsed brake hose
An old rubber brake hose can break down internally and act like a one-way valve - it lets pressure through but not back, holding the caliper applied. This causes a drag that mimics a stuck caliper but is actually the hose.
Prevent and fix
Service the guide pins and boots at every brake job, keep the fluid fresh, and replace aged hoses; see high-mileage calipers. A caliper that has already seized usually needs replacing - a loaded unit is easiest. Fit quality pads and hardware.