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Combination Vehicles Practice Question 21

Required for Class ACombination Vehicles · Question 21

The fifth wheel should be greased:

• AOnce a year
• BPer manufacturer schedule and inspected for wear regularly
• CNever
• DOnly by the driver

Correct answer: B. Per manufacturer schedule and inspected for wear regularly

Why: Fifth wheels need lubrication on the upper plate to allow free articulation and reduce wear on the kingpin. Follow the maintenance schedule.

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

• Q30. Stopping distance for a fully loaded combination vehicle is:
• Q43. When parking a combination vehicle, you should:
• Q56. When sliding the fifth wheel forward, the load on the steering axle:
• Q5. After backing under the trailer, you should:
• Q18. Cargo loaded too far forward can:

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.