CDL Air Brakes

First published: September 1, 2026Last verified: September 1, 2026Reviewed by the CertQuestUSA team

TL;DR

CDL Air Brakes: a 77-question practice bank for the real CDL Permit & Endorsement Exams standard, 3 full papers of 25 questions each with no repeats, every question citing the real regulation it comes from.

Where these questions come from

Every question in this bank cites a real source -- primarily FMCSA CDL Manual (84%) and 49 CFR (16%) of this exam's citations.

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3

full papers, no repeats

25

questions per paper

77

questions in the bank

What this exam covers

Air Brake System Parts31%
Dual Air Brake Systems12%
Inspecting Air Brake Systems26%
Using Air Brakes31%

5 real sample questions

What powers the air compressor on a commercial motor vehicle with air brakes?

A. It is connected to the engine through gears or a v-belt

B. It runs on a separate 12-volt electric motor

C. It is powered by the vehicle’s hydraulic pump

D. It draws power from the trailer’s electrical system

Source: FMCSA CDL Manual §5.1.1

What does the supply pressure gauge, connected to the air tank, tell the driver?

A. How much force is being applied to the brake pedal

B. How much air pressure is stored in the air tanks

C. The engine oil pressure

D. The distance traveled since the last brake inspection

Source: FMCSA CDL Manual §5.1.9

Before driving a vehicle with a dual air brake system, the driver should allow the compressor to build up at least what minimum pressure in both the primary and secondary systems?

A. 60 psi

B. 85 psi

C. 100 psi

D. 150 psi

Source: FMCSA CDL Manual §5.2

In a dual air brake system, the low air pressure warning light and buzzer must come on before pressure drops below what value in either system?

A. 45 psi

B. 60 psi

C. 90 psi

D. 125 psi

Source: 49 CFR 393.51

In an air-operated disc brake, what component replaces the s-cam to apply clamping force?

A. A vacuum booster

B. A power screw turned by the slack adjuster

C. A second brake pedal

D. The alcohol evaporator

Source: FMCSA CDL Manual §5.1.8

Real-world data for this exam

Heavy and Tractor-Trailer Truck Drivers: real median wageMay 2025$58,640/yr Part of the real CDL Driver career pathExplore ›

Frequently asked questions

What does the CDL Air Brakes practice test on CertQuestUSA include?

The CDL Air Brakes practice test includes a 77-question bank covering the real CDL Permit & Endorsement Exams standard, organized into 3 full papers of 25 questions each with no repeats. Every question cites the real regulation it comes from, such as the FMCSA CDL Manual.

What topics are covered on the CertQuestUSA CDL Air Brakes practice test?

The test covers four key domains: Air Brake System Parts (31%), Inspecting Air Brake Systems (26%), Using Air Brakes (31%), and Dual Air Brake Systems (12%). Each question is sourced directly from the FMCSA CDL Manual.

Is there a free diagnostic test available for CDL Air Brakes on CertQuestUSA?

Yes, CertQuestUSA offers a free diagnostic with 10 real questions across the exam's domains, requiring no sign-up. At the end, you receive a domain-by-domain breakdown of your performance.

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