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Air Brakes Practice Question 44

Restriction L if not passedAir Brakes · Question 44

When uncoupling, before disconnecting the air lines you should:

• AApply the tractor parking brake
• BApply the trailer parking brakes by pulling the red knob, then disconnect
• CDrive forward
• DRelease all air pressure first

Correct answer: B. Apply the trailer parking brakes by pulling the red knob, then disconnect

Why: Set the trailer brakes (pull the red knob) so the trailer holds itself, then disconnect glad hands. Failing to set trailer brakes can let the trailer roll.

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

• Q30. The most common cause of brake fade on a long downgrade is:
• Q43. The tractor protection valve closes automatically when trailer air pressure drops to:
• Q57. When climbing a long upgrade, brake adjustment should:
• Q8. When inspecting the air brake system, you should first build pressure to:
• Q21. The parking brake control on most newer trucks is:

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.