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Combination Vehicles Practice Question 28

Required for Class ACombination Vehicles · Question 28

When uncoupling a trailer, the order generally includes:

• ALower landing gear before disconnecting glad hands
• BLower landing gear, set trailer brakes, disconnect lines, release fifth wheel, slowly drive out
• CDrive away first, then disconnect
• DRelease fifth wheel before setting trailer brakes

Correct answer: B. Lower landing gear, set trailer brakes, disconnect lines, release fifth wheel, slowly drive out

Why: The full sequence: position trailer, lower landing gear to firm contact, set trailer parking brakes, disconnect glad hands and pigtail, pull fifth wheel release, slowly drive out from under the trailer.

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

• Q58. When making a long left turn at an intersection, you should:
• Q7. The trailer's landing gear should be:
• Q20. When checking trailer brakes via the hand valve, you should:
• Q34. Tracks of the tractor and trailer in a tight right turn should be:
• Q47. When driving across railroad tracks with a low-clearance trailer (lowboy), 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.