The stopping power of the spring brakes depends on the adjustment of the service brake. Which factor does this refer to?

• A. The air pressure in the tanks
• B. The adjustment of the service brake
• C. The weight of the vehicle
• D. The road grade

Answer: (B)

Spring brakes are held back by air pressure in the service brake system. When you apply the service brakes, that pressure is used to release the spring-loaded parking brakes, allowing the brakes to do their work. If the service brakes aren’t adjusted correctly, the release may not happen fully, or the engagement may not be consistent, so the spring brakes won’t provide their full stopping power. Proper service brake adjustment ensures the air pressure can reliably release the springs and let the braking system work at its best. The other factors—tank air pressure, vehicle weight, and road grade—affect braking in general, but the specific ability of the spring brakes to contribute stopping power largely comes down to how well the service brakes are adjusted.