71. Why should you not use the trailer hand brake to straighten out a jackknifing trailer?
Detailed Explanation
The correct answer is "b. Because the brakes on the trailer wheels cause the skid in the first place.". This question tests controlled braking, heat management, and maintaining steering control. Because the prompt uses negative wording, identify the normally correct safety rules first, then select the exception.
Correct Answer: b. Because the brakes on the trailer wheels cause the skid in the first place.
Why This Matters on the CDL Test
This question belongs in your brake safety review. Pay close attention to pressure limits, inspection steps, stopping distance, and warning signs because brake-system mistakes are a common reason CDL applicants miss endorsement questions.
How to Remember It
Say the rule in your own words, then explain why the wrong answers are unsafe or incomplete. That habit makes similar Combination Vehicles questions easier when the exam changes the wording.
Answer Review
Choose "b. Because the brakes on the trailer wheels cause the skid in the first place." because this answer matches the safe CDL action for brake system safety. On the knowledge test, the safest answer is usually the one that protects space, control, visibility, legal compliance, or inspection accuracy before the vehicle is put at risk.
Why the other answers are weaker
- a. Because the brake handle is too hard to reach."a. Because the brake handle is too hard to reach." does not best answer this brake system safety question. When you see a similar option on the CDL permit test, compare it against the exact safety rule and choose the answer that prevents the most immediate risk.
- c. Because the brakes on the trailer wheels will not respond to the hand brake."c. Because the brakes on the trailer wheels will not respond to the hand brake." does not best answer this brake system safety question. When you see a similar option on the CDL permit test, compare it against the exact safety rule and choose the answer that prevents the most immediate risk.
Test-Day Checklist
- Read the question once for the topic, then read it again for the exact CDL action being tested in Combination Vehicles.
- Eliminate answers that sound convenient but skip an inspection, warning sign, or safety step.
- Say the correct rule out loud before moving on so you can recognize it when the exam changes the wording.
Ready to practice for real?
Take our free, full-length Combination Vehicles practice test. Simulates the actual DMV exam with timed questions.
Start Practice TestRelated Questions
60. The tractor protection valve will close and the trailer emergency brakes will come on when there is a major leak in the________ brake line.
98. Charge the trailer air brake system and check that the trailer rolls freely. Then stop and pull out the trailer air supply control valve. Pull gently on the trailer with the tractor to check that the trailer emergency brakes are on.
99. Charge the trailer air brake system and push the air supply knob in. Shut the engine off. Step on and off the brake pedal several times to reduce the air pressure in the tanks. The trailer air supply control should pop out when the air pressure falls
Air pressure in the ____ air line is controlled by either the foot brake or trailer hand brake.
Using the trailer hand brake while experiencing a trailer jackknife will:
Keep Studying Combination Vehicles
Question pages help you review one rule at a time. To build test-day speed, move back into the full Combination Vehicles practice test and answer a mixed set without looking at the explanation first.
State CDL Practice Paths
After you understand this answer, use a state practice path to connect the federal CDL rule with the DMV test pages drivers search for most.