In a duo-servo type drum brake design, which shoe is typically longer and thicker?

• A. The primary shoe
• B. The secondary shoe
• C. Both shoes are the same
• D. None of the above

Answer: (B)

In a duo-servo type drum brake design, the secondary shoe is typically longer and thicker compared to the primary shoe. This design is specifically engineered to enhance braking efficiency. The secondary shoe, which is located on the rear side of the drum, benefits from the rotation of the drum during braking. As the brakes are applied, the secondary shoe gets pushed more forcefully against the drum due to the rotation direction, thereby increasing its braking effectiveness.

The longer and thicker design of the secondary shoe allows it to bear more force and create greater friction area against the drum, which is crucial for optimal brake performance. This design reduces the risk of brake fade and ensures the braking system can handle higher loads compared to a primary shoe. The primary shoe, in contrast, is generally shorter and thinner, serving a different role in the braking process.

In summary, the characteristics of the secondary shoe in a duo-servo brake system enable improved braking performance, making it a pivotal component in the overall function of the drum brake.