Air Brakes
This endorsement is required for driving a vehicle with air brakes. To receive this endorsement, applicants must pass a written test. The test consists of 25 multiple choice questions. Each question has three answer choices. To pass, the applicant must answer at least 20 questions correctly. Test questions come from the Iowa Commercial Driver License Manual. Questions come from the chapter covering: Air Brakes. The Air Brakes endorsement may be used with the Class A, B or C CDL.
Number of Question
Passing Score
7. The rods in S-cam brakes move the slack adjusters when air pressure is added to the brake chambers. This air pressure is added to the chambers when the driver:
Explanation
When pressing the brake pedal in a vehicle with S-cam brakes, air will enter the brake chambers. The added air pressure will push out the rods and move slack adjusters, twisting the brake camshafts.
8. What do air brakes use to make the brakes work?
Explanation
Many large CMVs are equipped with air brakes. An air braking system uses compressed air to operate.
9. If the safety relief valve in an air brake system is releasing air:
Explanation
The safety relief valve in an air brake system releases air if necessary to prevent pressure in the system from becoming too high. If the valve starts releasing air, there is something wrong. Have a mechanic fix the problem.
10. What should happen before the air pressure in an air brake system tank falls below 55 psi?
Explanation
The low air pressure warning signal must activate before the air supply pressure drops below 55 psi in the air tank. If the warning signal does not turn on when being tested during an inspection, the vehicle is not safe to drive.
11. Do not operate a vehicle if any brake drums have cracks that are larger than ____ of the width of the friction area.
Explanation
Before beginning a trip, it is important to check the brake drums during your walk-around inspection. It is unsafe to drive if any brake drum has a crack more than one half of the width of the friction area.
12. Foundation brakes are used:
Explanation
