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Combination Vehicles Practice Question 61

Required for Class ACombination Vehicles · Question 61

Failing to set the trailer parking brake before uncoupling can cause:

• AThe trailer to roll away once the fifth wheel is released
• BBetter braking
• CEngine stall
• DABS activation

Correct answer: A. The trailer to roll away once the fifth wheel is released

Why: Set the trailer parking brake before disconnecting air. Otherwise once you pull out from under, the trailer can roll on grade or under wind.

How this question fits the Combination test

Articulated vehicles fail in unique ways: trailer swing under braking, rearward amplification under steering, and jackknife under loss of traction. Combination Vehicle knowledge is required for any Class A applicant under 49 CFR 383.111.

Study technique for this topic

Walk through the coupling sequence verbally until it's second nature. Know the safe-rolling rearward amplification factor, the difference between trailer service brakes and parking brakes, and what creates the conditions for a tractor jackknife.

Related Combination practice questions

• Q9. The coupling height check before backing under the trailer is critical because:
• Q22. Air lines and electrical cables between tractor and trailer must be:
• Q35. Antilock brakes on a tractor without ABS on the trailer:
• Q48. The trailer brake valve (hand valve) is intended for use:
• Q62. When the trailer landing gear sticks during raising or lowering, you should:

Continue your CDL preparation

The Combination Vehicles portion of the CDL knowledge exam covers more than this single question. Use this site's full Combination Vehicles 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.