The brake wheel cylinder uses the hydraulic pressure generated by the brake master cylinder to force pistons to press the brake shoes against the brake drum. When the brake shoes come into contact with the brake drum, the wheels slows down or stop, slowing down or stopping the vehicle.
Most brake wheel cylinders wear over time and are unable to hold the hydraulic pressure, causing brake fluid to leak. Once it fails, then it will need to be replaced.
Most manufacturer factory warranties will cover a brake wheel cylinder under the bumper-to-bumper warranty section of the factory warranty. For extended coverage of a brake wheel cylinder after the factory warranty has expired, an extended auto warranty is an option.