South Dakota CDL — Air Brakes practice
South Dakota CDL — Air Brakes: Safe Driving Practices practice test
Following distance, scanning, blind spots, using your lights, and the habits that prevent crashes and keep you in control.
Content reviewed against official driver handbooks · August 12, 2026
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12 sample Safe Driving Practices questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.
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1. Section 11's air warning device test names three low air warning devices. A buzzer and a light are two of them. What is the third?
Correct answer: A flag
The test names the buzzer, the light and the flag. You fan the pressure down with the key or electrical power on and identify the level where they activate, which should be before the gauge falls under 55 psi.
Source: South Dakota Commercial Driver License Manual — Section 11.1.2, Air Brake or Hydraulic Brake Check
2. Section 2 lists what to check regularly while a trip is under way. Which item on that list applies only if your vehicle has air brakes?
Correct answer: The air pressure gauge
Among the in-trip checks, the manual lists the air pressure gauge with the note that it applies if you have air brakes. The other instruments, the mirrors, the tires and the cargo are checked on every vehicle.
Source: South Dakota Commercial Driver License Manual — Section 2.1.6, Inspection during a Trip
3. The manual compares the way an air-operated disc brake squeezes its disc to a familiar tool. Which one?
Correct answer: A large c-clamp
In a disc brake, a caliper's lining pads grip the rotor from both sides when the power screw tightens. The manual likens that action to a large c-clamp.
Source: South Dakota Commercial Driver License Manual — Section 5.1.8, Foundation Brakes
4. In what way does the manual say air-operated disc brakes work like s-cam brakes?
Correct answer: Both use a brake chamber and slack adjuster worked by air pressure
Disc brakes start the same way s-cam brakes do, with air working a brake chamber and slack adjuster. The difference comes next: the slack adjuster turns a power screw where a drum brake would turn an s-cam.
Source: South Dakota Commercial Driver License Manual — Section 5.1.8, Foundation Brakes
5. Grease or oil on a brake lining, pad, drum or disc reduces braking friction. What other danger does Section 11 say brake contaminants can create?
Correct answer: A fire hazard
Section 11 says contaminants on the brakes can cut braking friction, raising the risk of a crash, and can also create a fire hazard. Where the parts are accessible, you inspect the linings or pads and the drum or disc for grease, oil and similar contamination.
Source: South Dakota Commercial Driver License Manual — Section 11.5.2, Brake Contaminates
6. Air brakes are really three braking systems. Which one puts the brakes on and lets them off as you work the brake pedal in ordinary driving?
Correct answer: The service brake system
The service brake system handles normal driving and responds to the brake pedal. The parking brake system works from the parking brake control, and the emergency brake system borrows parts of the other two to stop the vehicle if the brake system fails.
Source: South Dakota Commercial Driver License Manual — Section 5, Air Brakes
7. You find that brakes fitted with automatic slack adjusters are out of adjustment. What does the manual recommend?
Correct answer: Get the vehicle to a repair shop without delay
Out-of-adjustment brakes on a vehicle with automatic adjusters point to a mechanical problem, so the manual recommends having a repair facility correct it promptly. Adjusting by hand is meant only as a temporary step in an emergency.
Source: South Dakota Commercial Driver License Manual — Section 5.3.2, During Step 5 Walk-around Inspection
8. On the external inspection you check the brake lines and hoses. What does Section 11 say a loss of air pressure there may cause?
Correct answer: Wheel lockup
The "Why Inspect" note for brake lines and hoses says losing hydraulic fluid may cut brake power and response, while losing air pressure may cause wheel lockup. You check that hoses and lines are not leaking, cracked, worn or frayed and that couplings and fittings are secure.
Source: South Dakota Commercial Driver License Manual — Section 11.5.2, Brake Lines / Hoses / Leaks
9. Can a driver switch an automatic front wheel limiting valve on or off from the cab?
Correct answer: No, the driver has no control over these valves
The cab control marked "normal" and "slippery" belongs to the manual front brake limiting valve on some vehicles made before 1975. The automatic valves found on many vehicles work by themselves, and the manual says the driver cannot control them.
Source: South Dakota Commercial Driver License Manual — Section 5.1.13, Front Brake Limiting Valve
10. While you are driving, the safety relief valve on your first air tank lets air out. How does the manual read that?
Correct answer: Something is wrong, and a mechanic should fix the fault
The safety valve keeps excess pressure from damaging the first tank and everything downstream, and it normally opens at about 150 psi, well above governor cut-out. If it releases air, the manual says something is wrong and a mechanic should repair the fault.
Source: South Dakota Commercial Driver License Manual — Section 5.1.6, Safety Valve
11. Before troubleshooting a brake adjustment problem, the manual sends you to the adjuster manufacturer's own service manual. What reason does it give?
Correct answer: Automatic slack adjusters come from different makers and do not all work alike
The note in the walk-around inspection points out that several manufacturers build automatic slack adjusters and their designs differ in how they operate. The right troubleshooting steps therefore depend on the specific make.
Source: South Dakota Commercial Driver License Manual — Section 5.3.2, During Step 5 Walk-around Inspection
12. You are about to pull out in a truck with a dual air system. How much pressure should the compressor first build in both the primary and the secondary systems?
Correct answer: At least 100 psi
The manual says to give the compressor time to bring both systems up to a minimum of 100 psi before driving, while you watch both gauges (or both needles) and the low air warning light and buzzer.
Source: South Dakota Commercial Driver License Manual — Section 5.2, Dual Air Brake
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