Free Practice Questions for MS CDL Air Brakes
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7 Job WikiKey Facts: MS CDL Air Brakes Exam
About 125 psi
Air compressor governor cut-out pressure
Mississippi CDL Manual Section 5
55 psi
Threshold below which low air warning must activate
Mississippi CDL Manual Section 5.1.11
20-45 psi
Pressure range where spring brakes automatically engage
Mississippi CDL Manual Section 5
About 32 ft
Distance air brake lag adds at 55 mph on dry pavement
Mississippi CDL Manual Section 5
The Mississippi CDL Air Brakes knowledge test is based on Section 5 of the Mississippi CDL Manual, and federal rules (49 CFR 383.135) require at least 80% on each CDL knowledge test. Mississippi DPS lists a $16 6-month CDL learner's permit and a $55 5-year CDL. Key figures include governor cut-in about 100 psi and cut-out about 125 psi, a low air warning before 55 psi, spring brakes fully on at 20 to 45 psi, and static leakage under 2 psi per minute for single vehicles.
Sample MS CDL Air Brakes Practice Questions
Try these sample questions to review concepts for the MS CDL Air Brakes exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 220+ question experience with AI tutoring.
1Section 5 of the Mississippi CDL Manual says air brakes are really three different braking systems. What are they?
2Which part of an air brake system applies and releases the brakes when you use the brake pedal during normal driving?
3How does Section 5 describe the emergency brake system?
4What does the air compressor do in an air brake system?
5Your vehicle's air compressor has its own oil supply. What does Section 5.1.1 tell you to do?
6What is the job of the air compressor governor?
7At about what tank pressure does Section 5.1.2 say the governor stops the compressor from pumping (cut-out)?
8During the governor check, you step on and off the brake with the engine idling. At about what pressure should the gauge start rising again?
9If the air compressor stops working, what does Section 5.1.3 say about the air storage tanks?
10Why must air storage tanks be drained?
About the MS CDL Air Brakes Exam
The Mississippi CDL Air Brakes Knowledge Test is required for drivers who will operate commercial vehicles with air brakes, including air-over-hydraulic brakes. Passing it avoids or removes the L (no air brake) restriction. Mississippi DPS gives the test, which is based on Section 5 of the Mississippi CDL Manual. Independent practice by OpenExamPrep covers air brake parts, warning devices, spring and parking brakes, ABS, dual systems, the air brake inspection, and safe braking. These multiple-choice questions are a study aid, not an official-format simulation, and they do not replace the skills test.
Exam sponsor: Mississippi Department of Public Safety Driver Service Bureau. The requirements and fees below concern the certification or admission exam, separate from our free practice resources.
Assessment
A multiple-choice knowledge test administered by Mississippi DPS driver license stations covering Section 5 of the Mississippi CDL Manual. Passing this exam removes the 'L' restriction (no air brakes) from a commercial driver license.
Time Limit
Not published by Mississippi DPS
Passing Score
80% on each CDL knowledge test
Exam / Certification Fees
$16 CDL learner's permit valid 6 months; $55 CDL 5-year license (no separate air brake fee is listed)
Exam sponsor websiteFees, 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.
Air Brake System Parts
The three braking systems, compressor and governor (cut-in about 100 psi, cut-out about 125 psi), air tanks and drains, alcohol evaporator, safety valve (usually 150 psi), brake pedal, foundation brakes, and pressure gauges.
Warning Devices and Controls
The low air pressure warning (before 55 psi; 80 to 85 psi is common on large buses), wig wags, the stop light switch, and front brake limiting valves.
Spring Brakes, Parking Controls, and ABS
Spring brakes (fully on at 20 to 45 psi), the yellow parking brake knob, modulating and dual parking control valves, and ABS requirements, lamps, and limits.
Dual Air Brake Systems
Primary and secondary systems, building at least 100 psi in both before driving, and what happens when one system loses pressure.
Inspecting Air Brake Systems
Compressor belt, slack adjusters (about 1 inch limit; automatic since 1994), drums and linings, governor test, static and applied leakage limits, low air warning and spring brake tests, build-up rate (85 to 100 psi in 45 seconds), and parking and service brake tests.
Using Air Brakes
Normal and emergency stops, braking with ABS, brake lag (about 32 feet at 55 mph), brake fade, downgrade braking technique, low air pressure, and parking brake rules.
Preparing for the MS CDL Air Brakes Exam
What You Need to Know
- Passing score: 80% on each CDL knowledge test
- Assessment: A multiple-choice knowledge test administered by Mississippi DPS driver license stations covering Section 5 of the Mississippi CDL Manual. Passing this exam removes the 'L' restriction (no air brakes) from a commercial driver license.
- Time limit: Not published by Mississippi DPS
- Exam / certification fees: $16 CDL learner's permit valid 6 months; $55 CDL 5-year license (no separate air brake fee is listed) 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
MS CDL Air Brakes: Suggested Study Strategy
Frequently Asked Questions
What is the purpose of the Mississippi CDL Air Brakes test?
The test determines whether a commercial driver understands how to safely operate and inspect vehicles equipped with air brakes. Passing this test prevents or removes the 'L' restriction (No Air Brakes) on a CDL.
What pressure should the air compressor governor cut out and cut in?
Section 5.1.2 of the Mississippi CDL Manual says the governor cuts out at around 125 psi and cuts in at around 100 psi. Section 5.3.3 says to check your vehicle's specifications; the manual also refers to cut-out in the 120 to 140 psi range.
When must the low air pressure warning device activate?
Section 5.1.11 says a visible warning must come on before tank pressure falls below 55 psi (or one-half the governor cut-out pressure on older vehicles). On large buses, warning devices commonly signal at 80 to 85 psi.
At what pressure do spring parking brakes automatically engage?
Section 5.1.14 says tractor and straight truck spring brakes come fully on when air pressure drops to 20 to 45 psi, typically 20 to 30 psi. Don't wait for them; stop safely as soon as the low air warning comes on.
What are the maximum acceptable air leakage rates during inspection?
For single vehicles, air leakage should not exceed 2 psi per minute with the engine off and brakes released (static), or 3 psi per minute with the service brake applied. For combination vehicles, the limits are 3 psi per minute static and 4 psi per minute applied.
What is the proper braking technique on a long, steep downgrade?
Drivers should shift into a low gear before starting down the grade, then apply the brakes firmly enough to feel a definite slowdown to 5 mph below the safe speed, release the brakes, and repeat this cycle (snubbing technique) as speed reaches the safe speed again.
Are these practice questions the same as the official Mississippi test?
No. This is independent practice by OpenExamPrep built from Section 5 of the Mississippi CDL Manual. It is a multiple-choice study aid, not a copy or simulation of the official DPS test, and it does not replace the skills test.