CDL AIR BRAKE Cheat Sheet 2026

The 30 highest-yield CDL AIR BRAKE facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. A key safety rule states that a driver should never push the brake pedal down when the spring brakes are on. Why is this? → It can damage brake components due to the combined force of the springs and air pressure.
2. What is the primary function of the air compressor in an air brake system? → To pump air into the storage tanks
3. Which of the following conditions will cause the spring brakes to apply automatically? → Air pressure in the main system drops to a low level, typically in the 20-45 psi range.
4. What should you do if your low air pressure warning activates? → Stop immediately and safely park the vehicle.
5. When driving a vehicle equipped with ABS, how should you apply the brakes in an emergency? → Apply the brakes firmly and hold them.
6. What activates the parking brakes in an air brake system? → Spring pressure when air is removed.
7. What should you do if your parking brakes won’t release due to frozen brake components? → Use a heater or other method to warm the brakes.
8. What is the purpose of a jake brake (engine compression brake)? → To use engine compression to slow the vehicle, reducing reliance on service brakes
9. What does a drain cock (drain valve) allow you to do on an air tank? → Manually release air pressure from the tank to drain moisture
10. What is the primary function of the S-cam in a foundation brake system? → To force the brake shoes apart and against the brake drum.
11. In a typical dual air brake system on a two-axle truck, how are the two systems usually split? → One system operates the front axle, and the other operates the rear axle.
12. Which air tank typically accumulates the most water and oil contamination? → Supply (wet) tank
13. A driver is operating a vehicle in freezing temperatures. Which component is specifically designed to help prevent ice from forming in the air brake valves? → Alcohol evaporator
14. How often should air tanks be drained? → Daily, at the end of each shift
15. What happens to brake drums as they heat up during prolonged braking? → They expand, which can reduce contact with brake shoes and lessen braking force
16. During a pre-trip inspection, what should you do with manual drain valves on air tanks? → Open them to drain moisture, then close them before driving
17. An air dryer is sometimes installed in an air brake system. What is its role in relation to the air tanks? → It removes moisture from the compressed air before it enters the tanks
18. What is the primary safety advantage of a dual air brake system? → It provides braking capability even if one of the two systems fails.
19. You are driving a vehicle with a dual air brake system. The low air pressure warning light and buzzer come on. What is the safest course of action? → Stop and safely park the vehicle as soon as possible.
20. While driving a truck with a dual air brake system, a failure occurs in the primary system. Which of the following is the most likely outcome? → Stopping distance will be increased, and the secondary system will still provide braking.
21. How is the air compressor typically driven on a commercial vehicle? → By the vehicle's engine via belt or gear
22. What should you do if the air pressure gauge shows a continuous drop while the vehicle is parked with the engine off? → Investigate for air leaks before driving the vehicle
23. What is the primary function of the air compressor governor in an air brake system? → To control when the air compressor pumps air into the storage tanks.
24. The emergency brake system in a vehicle with air brakes uses parts of which two other systems? → The service brake and the parking brake systems.
25. Which of the following scenarios describes a failed air pressure buildup test, requiring immediate mechanical attention? → The air pressure takes 55 seconds to build from 85 to 100 psi.
26. Which of the following are the three main types of foundation brakes used on vehicles with air brake systems? → S-cam, disc, and wedge brakes
27. What material are runaway truck ramp arrestor beds typically filled with? → Loose sand or pea gravel that creates resistance to stop runaway vehicles
28. How does brake fade affect stopping distance? → Stopping distance increases significantly as brakes overheat
29. What does 'total stopping distance' include for a truck equipped with air brakes? → Perception distance + reaction distance + brake lag distance + effective braking distance
30. If a vehicle has automatic drain valves on the air tanks, what is still required of the driver? → Check that the automatic drain valves are functioning properly during pre-trip inspection