New Jersey Air Brakes Practice Test

Which type of foundation brake is most commonly found on heavy vehicles?

1. Disc brakes

2. S-cam drum brakes

3. Hydraulic brakes

4. Ceramic brakes

The correct answer is: S-cam drum brakes

S-cam drum brakes are the most commonly found type of foundation brake on heavy vehicles due to their durability and effectiveness in managing the demands of high loads and extended stopping distances typical in large trucks and buses. This design utilizes a drum that rotates with the wheel and shoes that press against the drum surface to create friction and slow down the vehicle. The S-cam mechanism consists of a cam that, when rotated by the brake actuator, pushes the brake shoes outward against the drum. This design is particularly effective in providing strong braking force, making it suitable for the heavier weights and higher inertia of large vehicles. Furthermore, the robust construction of drum brakes allows them to withstand the extreme conditions frequently encountered in transportation, such as heat generated from prolonged use and exposure to varying environmental factors. In contrast, disc brakes, while also effective and becoming more common in some heavy vehicle applications for their quick cooling and consistent performance, are still less prevalent than S-cam drum brakes in traditional heavy-duty settings. Hydraulic brakes are typically found in lighter vehicles, and ceramic brakes are used mostly in performance cars due to their low weight and high thermal resistance, rather than in heavy-duty applications. Thus, S-cam drum brakes remain the standard in the heavy vehicle industry.