In a Duo-Servo Brake System, which shoe energizes the other?

In a Duo-Servo Brake System, the correct understanding is that the primary shoe energizes the secondary shoe. This occurs because of the design of the braking mechanism, where when the primary shoe is activated by braking force, it can pivot and push against the secondary shoe. This action causes the secondary shoe to also engage against the drum, thereby generating additional braking force.

The primary shoe’s role is crucial, as its movement not only activates the secondary shoe but also considerably enhances the overall effectiveness of the braking system. The design ensures that the braking force is maximized, providing better stopping power with less effort from the driver's foot on the brake pedal. The interaction between these two shoes in the Duo-Servo system highlights the principle of self-energization, which is a fundamental characteristic that distinguishes this type of braking system.