CDL Combination Vehicles Endorsement/Topics/Combination Air Brakes
Combination Air Brakes covers 15 questions in the QuizCram bank (15% of all questions), ranking as the biggest domain for the CDL combination vehicles endorsement exam. Questions are written against the official Original practice questions on the combination vehicles endorsement, written from the federal knowledge requirements in 49 CFR Part 383 and the public CDL manual facts. The real test is a multiple-choice knowledge test, and you need 80% to pass. Try the 3 free sample questions below to test your understanding of these core rules.
15 questions, the biggest topic. The ring is its size next to the biggest.
Combination air brakes1 of 3
The answer
Answer: D. The trailer hand valve is also called the trolley valve or Johnson bar, and it works the trailer brakes. The foot valve and treadle valve are names for the brake pedal, the relay valve and cut-out cock are other parts, and a glad hand or gooseneck is a coupling device.
Source: 6.2.1 - Trailer Hand Valve
Combination air brakes2 of 3
The answer
Answer: A. Do not use it while driving because it risks making the trailer skid. The hand valve is for testing the trailer brakes. Slowing on a downgrade, holding a parked trailer or fixing a jackknife with the hand valve would put brakes on the trailer wheels and could cause or worsen a skid.
Source: 6.2.1 - Trailer Hand Valve
Combination air brakes3 of 3
The answer
Answer: A. The tractor protection valve is controlled by the trailer air supply control valve in the cab. It does not prevent wheel lock in turns, set how hard the trailer brakes apply or charge the trailer tanks; its job is protecting the tractor's air if the trailer is lost.
Source: 6.2.2 - Tractor Protection Valve
QuizCram covers 15 practice questions in the Combination Air Brakes domain, mapped directly to the official examination blueprint.
The benchmark score is 80% (Multiple-choice knowledge test · 80% to pass (49 CFR 383.135) · item count set by your state).
Yes. All questions on QuizCram are written against official handbooks and blueprint specifications with legal citations.