How do Wheel Cylinders Work?
Your vehicle’s wheel cylinders are filled with brake fluid and connected to the brake master cylinder using high-pressure brake lines. For your brakes to work properly, the brake fluid needs to be clean, and the cylinders need to hold brake fluid regardless of the pressure in the lines.
Pushing on the brake pedal actuates the master cylinder. The master cylinder increases pressure inside your vehicle’s brake lines. The pressure inside the wheel cylinder increases as well, which pushes its pistons outward into the brake shoes. Brake shoes create friction against brake drums, which brings the vehicle to a stop.