Home › Practice › Air Brakes › Question 39

Air Brakes Practice Question 39

Restriction L if not passedAir Brakes · Question 39

A driver who hears continuous air leakage during a leak-down test should:

• AContinue with the trip
• BLocate and repair the source before driving
• CAdd more air and continue
• DCall a tow truck only if pressure drops to zero

Correct answer: B. Locate and repair the source before driving

Why: Audible leaks indicate a problem that will worsen. Find the source — chambers, lines, fittings — and repair before driving so brakes do not fail under load.

How this question fits the Air Brakes test

An air brake failure on a loaded combination vehicle can cause runaway, jackknife, or fire. The CDL Air Brakes test exists because air systems behave very differently from hydraulic brakes — drivers must understand pressure build, air loss tolerance, and stopping distance under load.

Study technique for this topic

Memorize the seven steps of the air brake pre-trip check, the leak-down rates for single and combination vehicles, the warning signal pressure threshold, and the spring brake automatic application pressure range. Practice the order of operations — never rely on muscle memory in the booth.

Related Air Brakes practice questions

• Q59. When you apply the trailer hand valve, you should not use it to:
• Q10. The proper braking technique for a long downgrade is:
• Q23. When the air brake system loses all pressure, what stops the vehicle?
• Q36. The compressor is most often driven by:
• Q50. Modulating valve (treadle valve) is the:

Continue your CDL preparation

The Air Brakes portion of the CDL knowledge exam covers more than this single question. Use this site's full Air Brakes bank to drill every topic, then test yourself with one of our state-specific practice sets to confirm you are ready for the actual DMV exam in your state. Always check your state's CDL handbook for any local addenda before the test day.

If you are still building your overall CDL foundation, start with the General Knowledge bank — every CDL applicant must pass it — and then work outward to the endorsements you plan to add.