What holds the primary and secondary shoes against the adjuster?

The anchor pin plays a crucial role in the drum brake system by securing the primary and secondary shoes against the adjuster. This component functions as a pivot point for the shoes, ensuring that they remain in their designated positions during braking. When the brakes are applied, the pressure exerted by the brake fluid pushes the shoes outward against the drum, and the anchor pin helps to maintain their alignment and stability as they press against the drum's inner surface.

In this context, the primary and secondary shoes need to maintain proper orientation to effectively generate friction against the brake drum. The anchor pin ensures that as either shoe moves, the other is also correctly positioned, thus maximizing brake efficiency. The other components listed, such as the caliper piston, brake pad, and connecting spring, serve different functions within the braking system, such as actuating the brakes, providing friction, or maintaining shoe tension, but it is the anchor pin that specifically secures the shoes against the adjuster.