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Free Practice Questions for South Dakota CDL Air Brakes

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Sample South Dakota CDL Air Brakes Practice Questions

Try these sample questions to review concepts for the South Dakota CDL Air Brakes exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 220+ question experience with AI tutoring.

1According to Section 5.1 of the South Dakota CDL Manual, what are the three distinct braking systems that make up an air brake system?
A.The hydraulic system, the electric system, and the mechanical system
B.The service brake system, the parking brake system, and the emergency brake system
C.The drum system, the disc system, and the retarder system
D.The primary air system, the secondary air system, and the auxiliary exhaust system
Explanation: Section 5.1 defines the three systems: the service brake system (applies and releases brakes during normal driving), the parking brake system (applies brakes when parked), and the emergency brake system (uses parts of service and parking systems to stop the vehicle if the air system fails).
2Which statement correctly describes how a commercial vehicle's air compressor is driven and lubricated?
A.The engine drives it through gears or a V-belt, and it may have its own oil supply or use engine oil
B.A wheel-speed sensor drives it, and brake fluid provides its lubrication
C.It runs only from battery power and has permanently sealed bearings
D.The transmission output shaft drives it, and power-steering fluid lubricates it
Explanation: Section 5.1.1 states that the engine drives the air compressor through gears or a V-belt. The compressor may have its own oil supply or be lubricated by engine oil; it pumps air into the storage tanks for the braking system.
3What is the typical air pressure at which the air compressor governor 'cuts in' to begin pumping air into the storage tanks?
A.Around 55 psi
B.Around 100 psi
C.Around 125 psi
D.Around 150 psi
Explanation: Section 5.1.2 states that when reservoir pressure falls to the 'cut-in' level (typically around 100 psi), the governor allows the compressor to start pumping air into the tanks again.
4At what air pressure does the air compressor governor typically 'cut out' to stop the compressor from pumping air into the tanks?
A.Around 85 psi
B.Around 100 psi
C.Around 125 psi (typically between 120 and 130 psi)
D.Around 175 psi
Explanation: Section 5.1.2 explains that when air tank pressure reaches the 'cut-out' level (typically around 125 psi), the governor stops the compressor from pumping air into the tanks.
5Why must compressed air storage tanks be drained regularly of moisture and compressor oil?
A.Water and oil collect in the bottom of the tanks; in cold weather the water can freeze and cause brake failure
B.Draining tanks increases engine horsepower
C.Oil and water make the air tanks too heavy for highway bridge limits
D.Draining tanks is only necessary during the annual vehicle registration inspection
Explanation: Section 5.1.4 explains that compressed air usually contains water and compressor oil, which collect in the bottom of the tanks. Water can freeze in cold weather and cause brake failure, so the tanks must be drained completely.
6How often should manual air tank drain valves be opened to expel collected water and oil?
A.Once every 30 days
B.At the end of each day's driving
C.Once every oil change interval (approximately 15,000 miles)
D.Only when the low air pressure buzzer sounds
Explanation: Section 5.1.3 states that manual drain valves must be opened at the end of each day of driving to drain moisture and oil from the bottom of each air tank.
7What is the function of an alcohol evaporator in a commercial vehicle's air brake system?
A.It burns alcohol to heat the passenger cabin
B.It introduces alcohol vapor into the air system to prevent moisture from freezing in air brake valves during cold weather
C.It filters engine exhaust emissions to meet EPA standards
D.It cools the compressed air before it enters the foundation drums
Explanation: Section 5.1.4 states that alcohol evaporators put alcohol into the air system to reduce the risk of ice forming in air brake valves and lines during cold weather. Drivers must check and fill the alcohol level daily during cold weather.
8At what pressure is the safety relief valve on an air storage tank set to open?
A.55 psi
B.100 psi
C.125 psi
D.150 psi
Explanation: Section 5.1.5 states that a safety relief valve is installed in the first tank to protect the system from excessive pressure. It is typically set to open at 150 psi if the governor malfunctions.
9What happens when a driver depresses the brake pedal (foot valve / treadle valve) in an air brake vehicle?
A.Air is released from the atmosphere into the compressor
B.Compressed air from the reservoirs is metered and directed to the brake chambers, with more pedal pressure delivering more air pressure to the brakes
C.Hydraulic fluid is forced into wheel cylinders
D.The engine automatically shuts down
Explanation: Section 5.1.6 explains that pushing the brake pedal opens a valve that sends air pressure from storage tanks to the brake chambers. Pressing harder delivers higher air pressure; releasing the pedal exhausts the air, releasing the brakes.
10Why is repeatedly pressing and releasing (fanning) the brake pedal hazardous in an air brake system?
A.It causes the brake pedal return spring to overheat
B.It lets compressed air out of the system faster than the compressor can build it back up, which can deplete tank pressure and trigger emergency spring brake lockup
C.It increases diesel fuel consumption by 40%
D.It causes the trailer to detach from the tractor
Explanation: Section 5.1.6 warns that every brake application and release exhausts a volume of compressed air. Fanning the pedal rapidly dumps air faster than the compressor can replenish it, dropping pressure below safe operating levels.

About the South Dakota CDL Air Brakes Exam

The South Dakota CDL Air Brakes knowledge test is a 25-question state assessment administered by South Dakota DPS Driver Licensing for applicants who need to operate air-braked commercial vehicles, including air-over-hydraulic systems. Air brakes are a qualification rather than an endorsement. Under SDCL 32-12A-23, failing the knowledge test or skills-testing without air brakes results in restriction L; testing in an air-over-hydraulic vehicle results in restriction Z. The manual prohibits interpreters for knowledge testing, while every skills-test part is conducted in English. Independent OpenExamPrep practice uses four-option questions based on Section 5 and is not an official test copy or simulation.

Exam sponsor: South Dakota Department of Public Safety (DPS), Driver Licensing Program. The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

A 25-question multiple-choice knowledge test at a South Dakota DPS exam station based on Section 5 of the South Dakota CDL Manual. Air brakes are a vehicle qualification rather than an endorsement. In the modernized skills test, failure on any part of the four-part air-brake inspection automatically fails the vehicle inspection test.

Time Limit

Not published by South Dakota DPS

Passing Score

At least 80% correct on each CDL knowledge test (49 CFR 383.135 and South Dakota DPS)

Exam / Certification Fees

$43 CLP; $43 CDL; no separate air-brake knowledge-test fee identified; third-party skills test may cost $150 plus tax per attempt

Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

CDL Manual Sections 5.1.1 to 5.1.13 (official weight not published)

Air Brake System Parts

Compressor, governor, air tanks and drain valves, alcohol evaporator, safety valve, foot pedal, S-cam and disc brakes, pressure gauges, low air warning device, stop light switch, and front brake limiting valves.

CDL Manual Sections 5.1.14, 5.1.15, and 5.4.8 (official weight not published)

Spring Brakes and Parking Controls

Spring brake engagement pressures, yellow parking control knob, compounding force hazards, modulating valves, and parking with hot or wet brake drums.

CDL Manual Sections 5.1.16 and 5.4.2 (official weight not published)

Antilock Brakes

Federal ABS mandate dates, yellow malfunction indicator lamps, electronic control unit function, and proper braking technique with ABS.

CDL Manual Section 5.2 (official weight not published)

Dual Air Brake Systems

Primary and secondary pneumatic circuits, minimum pressure required before driving, warning signal thresholds, and single-circuit failure handling.

CDL Manual Section 5.3 (official weight not published)

Inspecting Air Brakes

Slack adjusters and pushrod travel limits, drum and lining inspection, static and applied leakage limits, low air warning test, spring brake pop-out test, and compressor buildup rate.

CDL Manual Section 5.4 (official weight not published)

Using Air Brakes

Normal and emergency stops, brake lag distance, total stopping distance, brake fade mechanics, downgrade snub braking, and low air emergency stops.

CDL Manual Section 1, South Dakota DPS rules, SDCL 32-12A-23, and 49 CFR 383.95 (official weight not published)

Testing and Restrictions

Who must test, 80% passing score, L and Z air brake restrictions, retest waiting periods, and the mandatory vehicle inspection air brake check.

Preparing for the South Dakota CDL Air Brakes Exam

What You Need to Know

  • Passing score: At least 80% correct on each CDL knowledge test (49 CFR 383.135 and South Dakota DPS)
  • Assessment: A 25-question multiple-choice knowledge test at a South Dakota DPS exam station based on Section 5 of the South Dakota CDL Manual. Air brakes are a vehicle qualification rather than an endorsement. In the modernized skills test, failure on any part of the four-part air-brake inspection automatically fails the vehicle inspection test.
  • Time limit: Not published by South Dakota DPS
  • Exam / certification fees: $43 CLP; $43 CDL; no separate air-brake knowledge-test fee identified; third-party skills test may cost $150 plus tax per attempt Official sources

Using Our Practice Resources

  • Work through all 220 available questions
  • Review every answer and explanation
  • Track weak areas and revisit them
  • Use our AI tutor for tough concepts

South Dakota CDL Air Brakes: Suggested Study Strategy

1Memorize key system pressures: governor cut-in about 100 psi, governor cut-out about 125 psi, safety valve about 150 psi, low-air warning before 55 psi, and spring-brake pop-out at 20 to 45 psi.
2Remember leakage rate maximums: with brakes released, less than 2 psi/min (single) or 3 psi/min (combination); with brakes applied, less than 3 psi/min (single) or 4 psi/min (combination).
3Understand brake lag: air brakes take approximately one-half second for air to flow through the lines, adding about 32 feet of brake lag distance at 55 mph, for a total stopping distance exceeding 450 feet.
4Know SDCL 32-12A-23 restrictions: failing the knowledge test or testing without air brakes results in L; testing with air-over-hydraulic brakes results in Z.

Frequently Asked Questions

Is the air brake test considered an endorsement in South Dakota?

No. Air brakes are a vehicle qualification rather than an endorsement. If an applicant fails the air-brake knowledge test or takes the skills test in a vehicle without air brakes, restriction L applies under SDCL 32-12A-23 and 49 CFR 383.95.

What happens if I take my South Dakota CDL skills test in a vehicle with hydraulic brakes?

Your CDL will carry restriction L, which prohibits operation of an air-braked CMV (SDCL 32-12A-23 and 49 CFR 383.95). Testing in an air-over-hydraulic vehicle instead results in restriction Z, which prohibits operation of a full-air-brake-equipped CMV.

What are the acceptable air leakage rates during the pre-trip inspection?

Section 5.3 gives static limits of less than 2 psi in one minute for a single vehicle and less than 3 psi for a combination. In the applied check after governor cut-out and gauge stabilization, loss over 3 psi for a single vehicle or 4 psi for a combination in one minute is excessive.

At what air pressure must the low air pressure warning activate?

Section 5.1.11 requires the visible low-air warning before pressure drops below 55 psi, or one-half the governor cut-out pressure on older vehicles. A buzzer may also sound, and large buses commonly warn at 80 to 85 psi.

At what pressure do the emergency spring brakes automatically apply?

Section 5.1.14 indicates that tractor and straight truck spring brakes automatically pop out and apply mechanically when system air pressure drops into the range of 20 to 45 psi (typically between 20 and 30 psi). Drivers should pull over safely as soon as the low air warning sounds rather than waiting for spring brakes to lock up.

What is the proper technique for braking on long downgrades?

First shift into an appropriate low gear before starting down the hill. Once the vehicle reaches its designated safe speed, apply the brakes firmly enough to feel a definite slowdown until speed drops 5 mph below the safe speed (taking about three seconds), release the brakes, and repeat the process (snub braking) when speed returns to the safe threshold.

Are these practice questions identical to the official South Dakota air brakes test?

No. These are independent educational study questions written based on Section 5 of the South Dakota Commercial Driver License Manual and federal safety regulations. They are designed to help you understand air brake systems and prepare for testing, but they are not an official test copy or simulation.