CDL Air Brakes study guide
CDL Air Brakes · Work through your exam, one topic at a time.
The CDL air brakes knowledge test is the written exam a commercial driver takes to be certified to operate a vehicle equipped with air brakes. Passing it - along with the required vehicle inspection demonstration - is what allows the "No Air Brakes" restriction (an L code or similar, depending on the state) to be removed from a commercial learner's permit or license. The CDL Air Brakes study guide has 6 sections and about 1,910 words.
01Air Brake System Components and How They Work
Every air brake question sorts into two halves. The supply side makes and stores air: the engine-driven compressor pumps air through an air dryer (or an alcohol evaporator on older trucks) into the supply (wet) reservoir , then through check valves into the primary and secondary reservoirs.
323 words, about 2 min02Dual Air Brake Systems and Safety Features
A dual air brake system splits into a primary circuit (rear brakes) and a secondary circuit (front brakes). The foot valve has two separate sections fed by separate reservoirs, so a leak or ruptured line in one circuit cannot drain the other.
338 words, about 2 min03Inspecting Air Brake Systems (Pre-Trip and In-Service Checks)
Drain the tanks - moisture and oil collect at the bottom of every reservoir, including the wet tank. With the engine running, the gauge should climb from 85 to 100 psi in about 45 seconds.
334 words, about 2 min04Normal Braking Technique and Proper Use of Air Brakes
Air must travel from tank to chamber, so there is a lag between pedal and brake. Stopping distance is longer than in a car and grows quickly with speed.
284 words, about 1 min05Brake Failure, Warning Signals, and Emergency Procedures
Every air brake system warns you twice before the brakes quit. First, the low-pressure warning light and buzzer at about 60 psi - that is your signal to stop safely and find out why.
302 words, about 2 min06Parking Brakes, Hills, Water, and Adverse Conditions
Come to a full stop, apply the parking brake (yellow diamond knob), then release the service brake. On any grade, chock the wheels - spring brakes are strong, but the standard is chocks plus parking brake.
329 words, about 2 min