This set covers core air brake components, normal operation, warning devices, and foundational inspection steps.
01Air compressor
02Governor
03Reservoirs
04Brake chambers
05Warning devices
06Spring brakes
PRACTICE MODE
Air Brakes Test 1
Questions appear in a new order on each attempt. Choose one answer, review the explanation, and use Back or Next to move through the test.
Question 1 of 25Score 0
What three braking systems are commonly described in an air-brake vehicle?
Answer: Service, parking, and emergency The service system handles normal braking, the parking system holds the vehicle, and the emergency system uses parts of the other systems after a failure. Understanding each function is foundational air-brake knowledge. Study: Air Brakes — system overview
What is the job of the air compressor?
Answer: Pump air into the storage tanks The compressor supplies compressed air for the system and is usually engine driven. The governor controls when it loads and unloads. Study: Air Brakes — compressor
What does the air-compressor governor control?
Answer: When the compressor pumps air into the tanks The governor starts and stops compressor loading at designed cut-in and cut-out pressures. It helps maintain a usable pressure range. Study: Air Brakes — governor
Why must air tanks be drained?
Answer: To remove accumulated water and oil Moisture and oil can collect in reservoirs and harm the system, especially in freezing weather. Manual drains should be used as directed. Study: Air Brakes — reservoirs
At approximately what pressure does the safety relief valve commonly open?
Answer: About 150 psi A safety relief valve protects tanks and the rest of the system from excessive pressure and commonly opens near 150 psi. A valve that releases air may indicate a system problem needing service. Study: Air Brakes — safety valve
What is the purpose of an alcohol evaporator in some air-brake systems?
Answer: Help reduce ice formation in cold weather An alcohol evaporator can introduce alcohol vapor to reduce ice in valves and lines. Its level and operation must be checked according to the vehicle instructions. Study: Air Brakes — cold-weather equipment
What is meant by the foundation brakes?
Answer: The braking mechanisms at each wheel Foundation brakes are the wheel-end components that create friction to slow the vehicle. Drum systems commonly use brake shoes, drums, chambers, slack adjusters, and S-cams. Study: Air Brakes — foundation brakes
In an S-cam brake, what does the S-cam do?
Answer: Pushes the brake shoes against the drum Air pressure moves the chamber pushrod and slack adjuster, rotating the S-cam. The cam forces the shoes against the drum to create braking friction. Study: Air Brakes — S-cam brakes
Excessive slack-adjuster movement can indicate what?
Answer: Brakes may be out of adjustment Too much pushrod travel can reduce braking effectiveness and indicates an adjustment or mechanical problem. A qualified person should inspect and correct it. Study: Air Brakes — adjustment
Who should manually adjust automatic slack adjusters?
Answer: A qualified mechanic when repair is needed Automatic adjusters should normally maintain adjustment themselves. Repeated manual adjustment can hide a defect and should be handled by a qualified mechanic. Study: Air Brakes — automatic slack adjusters
What does an application-pressure gauge show?
Answer: How much air pressure is being applied to the brakes An application gauge shows the pressure the driver is sending to the brakes. A need for unusually high application pressure can signal adjustment or system problems. Study: Air Brakes — gauges
What do supply-pressure gauges show?
Answer: Pressure in the air tanks The primary and secondary gauges show reservoir pressure in a dual system. Drivers monitor them during buildup, testing, and operation. Study: Air Brakes — gauges
When must the low-air warning signal activate in a typical system?
Answer: Before pressure drops below 60 psi The low-air warning must come on before tank pressure falls below 60 psi, or at the manufacturer-specified higher point. Treat the warning as an urgent signal to stop safely. Study: Air Brakes — warning devices
How are brake lights activated on an air-brake vehicle?
Answer: An electric switch responds to air pressure from brake application An air-pressure-operated electrical switch turns on the brake lights when service brakes are applied. Other road users need that warning. Study: Air Brakes — brake-light switch
At what pressure range do spring brakes commonly begin to apply automatically?
Answer: About 20 to 45 psi Spring brakes commonly begin applying when system pressure falls into the 20-to-45 psi range, though vehicle specifications vary. Do not wait for automatic application; stop safely at the low-air warning. Study: Air Brakes — spring brakes
Why are powerful springs used in parking and emergency brakes?
Answer: They can apply brakes when air pressure is lost Air pressure normally holds spring brakes released. If pressure is removed, mechanical spring force can apply the brakes. Study: Air Brakes — spring brakes
What is the purpose of a dual air-brake system?
Answer: Provide two separate air circuits for greater safety Most modern heavy vehicles have two air circuits, commonly serving different axle groups. If one circuit fails, the other may retain some braking capability. Study: Air Brakes — dual systems
Before driving a dual air system, what pressure should both systems generally reach?
Answer: At least 100 psi Both system gauges should show at least 100 psi before driving, unless the manufacturer specifies otherwise. This confirms adequate operating pressure. Study: Air Brakes — dual systems
Why should a vehicle be chocked before some stationary air-brake tests?
Answer: To prevent unintended movement Tests may require releasing parking brakes or reducing system pressure. Wheel chocks and a safe location keep the vehicle from rolling. Study: Air Brakes — inspection safety
How is the low-air warning device commonly tested?
Answer: Turn electrical power on and fan the brake pedal to lower pressure With the vehicle secured, reducing air pressure should activate the warning before pressure falls below the required level. Follow the exact inspection procedure in the current state manual. Study: Air Brakes — low-air warning test
How is automatic spring-brake application commonly tested?
Answer: Continue fanning the brakes until the parking control pops out After the low-air warning test, continued pressure reduction should cause the parking-brake control to pop out in the vehicle’s specified range. The vehicle must be secured during this test. Study: Air Brakes — spring-brake test
How should service-brake operation be checked after the stationary tests?
Answer: Move slowly and apply the brake firmly At about walking speed, a firm service-brake application should stop the vehicle without pulling, unusual delay, or abnormal feel. Any problem requires repair before driving. Study: Air Brakes — service-brake test
During a static leakage test with brakes released, what loss is generally allowed for a single vehicle?
Answer: Less than 2 psi in one minute With a fully charged system, engine off, parking brake released, and service brakes released, a single vehicle should generally lose less than 2 psi in one minute. Follow the current manual’s exact setup. Study: Air Brakes — leakage test
During a static leakage test with brakes released, what loss is generally allowed for a combination vehicle?
Answer: Less than 3 psi in one minute A combination vehicle should generally lose less than 3 psi in one minute with brakes released during the static test. Excess loss indicates a leak that must be repaired. Study: Air Brakes — leakage test
During an applied leakage test, what loss is generally allowed for a single vehicle?
Answer: No more than 3 psi in one minute With the system charged, engine off, parking brakes released, and the service brake fully applied after pressure stabilizes, a single vehicle should generally lose no more than 3 psi in one minute. Study: Air Brakes — applied leakage test
Answer from memory so your first score shows which topics need work.
02
Review the explanations
Return to the cited handbook section whenever an idea is unclear.
03
Retake after review
Aim for consistent mastery, not memorizing the position of an answer.
FACT-CHECKED STUDY BASIS
Official handbook sources
Questions are original study material based on the standard CDL manual topics used by state licensing agencies. Requirements and test formats can vary by state, so always confirm details in your current state CDL manual.
Important: This independent study site is not affiliated with FMCSA or any state DMV. It does not replace the official handbook or professional instruction.