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 two, three or four answer choices. To pass, the applicant must answer at least 20 questions correctly. Test questions come from the South Carolina 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
1. To ensure normal stopping power, drivers of vehicles equipped with a front brake limiting valve should:
Explanation
Some pre-1975 vehicles have a front brake limiting valve, which has "normal" and "slippery" settings. The idea behind these valves was to limit the air pressure available to the front brakes when driving on slippery surfaces, and thereby reduce the danger of a front-wheel skid. Studies have found that this is not actually a concern, so if your vehicle has a front brake limiting valve, leave it in the "normal" position.
2. When leaving a vehicle unattended, a driver should:
Explanation
Always apply the parking brake when leaving your vehicle unattended.
3. When a brake pedal is pressed and the S-cam is turned, the S-cam:
Explanation
When a brake pedal is pressed and the S-cam is turned, the S-cam presses the brake shoes against the inside of the brake drum. This causes friction and will cause the vehicle to slow.
4. Foundation brakes are used:
Explanation
Foundation brakes are used at each wheel. The most common type is the S-cam drum brake.
5. While operating on a downgrade, you should brake until you reach a speed that is:
Explanation
While driving downhill, you should hold down the brake pedal until your vehicle reaches a speed 5 mph below your safe speed, then release the brake pedal. Repeat this process.
6. Brakes can get out of adjustment quickly, especially:
Explanation
