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Question 1 of 65
What does the air compressor governor control?
Correct answer: A. When the air compressor pumps air into the air storage tanks
Why: Governor controls cut-in (pump on) and cut-out (pump off) pressures, typically 100/125 psi.
Question 2 of 65
Air brake systems combine three different braking systems. They are:
Correct answer: A. Service, parking, and emergency brakes
Why: Service brakes: foot pedal. Parking brake: yellow knob. Emergency: parking system used in failure.
Question 3 of 65
What does the safety valve in the air compressor or supply tank protect against?
Correct answer: A. Too much pressure in the air system
Why: Safety relief valve typically opens at 150 psi to protect tanks.
Question 4 of 65
When the brake pedal is pressed, air pressure to the brake chambers:
Correct answer: A. Increases, applying force to the slack adjusters and S-cams
Why: Pressure rises in chambers, pushing rods that rotate slack adjusters and S-cams to apply brakes.
Question 5 of 65
When should you drain air tanks?
Correct answer: A. At the end of each day to remove water and oil
Why: Daily draining prevents corrosion and brake freeze-up.
Question 6 of 65
How much pressure should be lost in one minute with the engine off and brakes released?
Correct answer: A. No more than 2 psi (single) or 3 psi (combination)
Why: Static leak: ≤2 psi/min single, ≤3 psi/min combo. Section 5.1.13.
Question 7 of 65
How much pressure should be lost in one minute with the engine off and brakes applied (combination)?
Correct answer: A. No more than 4 psi
Why: Applied leakage limit: 3 psi single, 4 psi combination per minute.
Question 8 of 65
At what air pressure should the low-pressure warning device activate?
Correct answer: A. Below 60 psi
Why: Low-air warning must come on before pressure falls below 60 psi.
Question 9 of 65
At what pressure does the spring brake (parking) typically apply automatically?
Correct answer: A. Between 20 and 45 psi
Why: Springs in spring-brake chambers apply when air falls into the 20–45 psi range.
Question 10 of 65
What is the proper way to test the low-air warning?
Correct answer: A. Build pressure, shut off engine, fan brakes — warning must come on by 60 psi
Why: Pump pedal repeatedly to lower pressure; warning device must activate before 60 psi.
Question 11 of 65
When you make a normal stop with air brakes, you should:
Correct answer: A. Push the pedal down with steady pressure to slow smoothly
Why: Smooth steady application; release as you stop.
Question 12 of 65
Why must air tanks be drained?
Correct answer: A. To remove condensation that can freeze valves and lines
Why: Water and compressor oil collect at tank bottoms; if not drained they corrode tanks and freeze brakes.
Question 13 of 65
What does an "alcohol evaporator" do in the air system?
Correct answer: A. Reduces risk of ice in air brake valves in cold weather
Why: Alcohol evaporator vaporizes alcohol into the air system to inhibit ice.
Question 14 of 65
How is the parking brake applied on a vehicle with spring brakes?
Correct answer: A. Pull out the yellow diamond-shaped knob
Why: Yellow diamond: tractor parking. Red eight-sided: trailer air supply.
Question 15 of 65
What can keep spring brakes from applying when air pressure drops?
Correct answer: A. Caged or broken springs
Why: If springs are caged (manually released) or broken, the brakes cannot apply.
Question 16 of 65
Modulating control valves are used to:
Correct answer: A. Apply spring brakes gradually using a lever
Why: Some vehicles have a modulating valve to gradually apply spring brakes.
Question 17 of 65
ABS on air brake vehicles requires:
Correct answer: A. A yellow malfunction lamp on the dash
Why: Yellow ABS warning lamp on tractors; trailers have a yellow lamp on the left side.
Question 18 of 65
How can you test that ABS is working on a tractor?
Correct answer: A. Turn the key on; the yellow lamp should light briefly then go out
Why: Self-test illuminates lamp briefly. If it stays on, ABS has a fault.
Question 19 of 65
What should you do if the low-air warning comes on while driving?
Correct answer: A. Stop safely as soon as possible and find the cause
Why: Once warning sounds, brakes can fail with little additional pressure loss — stop now.
Question 20 of 65
Why use the parking brake any time you leave the vehicle?
Correct answer: A. To prevent rollaway
Why: Parking brake must be set whenever you leave the vehicle.
Question 21 of 65
Total stopping distance with air brakes is longer because:
Correct answer: A. Brake lag adds about 0.5 seconds (32 feet at 55 mph) compared to hydraulic
Why: Brake lag — time for air to travel through lines — adds distance.
Question 22 of 65
How are the brakes applied on the trailer using a hand-control valve?
Correct answer: A. Independently of the foot brake — should not be used for parking
Why: Hand valve applies trailer brakes only and should not be used for parking.
Question 23 of 65
Why should you never use the trailer hand valve to hold a parked vehicle?
Correct answer: A. Air may leak out, releasing the brakes
Why: Service brakes leak; only spring/parking brakes hold reliably.
Question 24 of 65
Air braking takes more time than hydraulic braking because:
Correct answer: A. Air must flow through lines to brake chambers
Why: Lag = time for air to travel and build pressure at chambers.
Question 25 of 65
What is the proper procedure to test air brake leakage on a combination vehicle?
Correct answer: A. Charge to governor cut-out, off engine, release brakes 1 min, apply brakes 1 min
Why: Static and applied leakage tests done with engine off, parking brake released and applied.
Question 26 of 65
Stab braking on vehicles without ABS is:
Correct answer: A. Apply brakes fully, release when wheels lock, reapply when wheels start rolling
Why: Stab braking provides emergency stopping without losing control.
Question 27 of 65
Brake fade results from:
Correct answer: A. Heat build-up and reduced friction
Why: Excessive heat reduces friction between linings and drums.
Question 28 of 65
Why are slack adjusters checked?
Correct answer: A. To ensure brakes are within proper adjustment for safe stopping
Why: Out-of-adjustment slack adjusters are a leading cause of brake failure.
Question 29 of 65
Manual slack adjusters should be:
Correct answer: A. Adjusted by a qualified mechanic only when out of adjustment
Why: FMCSA requires only qualified mechanics; even with manual ones drivers usually only inspect.
Question 30 of 65
Pushrod travel beyond legal limits indicates:
Correct answer: A. Brakes need adjustment
Why: Excessive stroke = out of adjustment.
Question 31 of 65
How do you know if the front brake limiting valve is in the "wet" or "dry" position?
Correct answer: A. Some older trucks have a switch — set "dry" for normal roads, "slippery" for slick (now generally removed)
Why: Older vehicles had this switch; modern trucks no longer use front brake limiting valves.
Question 32 of 65
What is a dual air brake system?
Correct answer: A. Two separate air brake systems sharing one set of controls
Why: One system operates rear axles, the other front axle and trailer (or vice versa).
Question 33 of 65
How can you tell if your dual brake system has a leak in one circuit?
Correct answer: A. Low-air warning activates and one system loses pressure
Why: Each circuit has its own gauge; one will fall.
Question 34 of 65
What is the safe operating range for air pressure?
Correct answer: A. About 100 to 125 psi
Why: Governor cut-in/out typically 100/125 psi.
Question 35 of 65
Foundation brakes use which mechanism on most trucks?
Correct answer: A. S-cam drum brakes
Why: S-cam drum brakes are the most common foundation brake on heavy trucks.
Question 36 of 65
Wedge brakes are:
Correct answer: A. A type of drum brake using a wedge between brake shoes
Why: Wedge brakes are less common but appear on some heavy vehicles.
Question 37 of 65
What are the air brake test steps before driving (in order)?
Correct answer: A. Static leak, applied leak, low-air warning, spring brake activation
Why: AAMVA Section 5.3.10 lists the seven-step in-cab brake check.
Question 38 of 65
How is the trailer air supply controlled?
Correct answer: A. Red eight-sided knob on dashboard
Why: Red knob: pull to charge trailer (out=disconnect, in=charged).
Question 39 of 65
When connecting a trailer, the order is:
Correct answer: A. Connect emergency line first, then service line, then push in red knob
Why: Emergency (supply) connects first to charge the trailer.
Question 40 of 65
When uncoupling, you must:
Correct answer: A. Pull out the red knob to apply trailer brakes
Why: Red knob OUT applies trailer parking brakes before disconnecting.
Question 41 of 65
What is the proper procedure to recover from an air-brake skid?
Correct answer: A. Release brakes, countersteer toward intended path
Why: Release brakes to allow steering, then countersteer.
Question 42 of 65
What is brake lag at 55 mph approximately?
Correct answer: A. 32 feet
Why: About 32 ft from the time you press the pedal until brakes apply.
Question 43 of 65
You can test trailer service brakes by:
Correct answer: A. Pulling forward at 5 mph and applying the trailer hand valve
Why: Hand valve at low speed checks trailer service-brake function.
Question 44 of 65
Which of these is true about modulating valves?
Correct answer: A. They allow gradual application of spring brakes
Why: Modulating spring-brake control valves allow proportional application.
Question 45 of 65
When you press the brake pedal, more pressure equals:
Correct answer: A. More braking force
Why: Greater pedal force => higher pressure to brake chambers => more force.
Question 46 of 65
What does the air dryer do?
Correct answer: A. Removes moisture from compressed air before it enters the tanks
Why: Air dryer removes water and oil before air enters the system.
Question 47 of 65
Why should air tanks have separate compartments or several tanks?
Correct answer: A. So a leak in one part does not lose the entire system
Why: Multi-tank systems isolate failures.
Question 48 of 65
You may legally drive a vehicle with the low-air warning device on if:
Correct answer: A. Never — stop immediately
Why: Low-air warning means stop and fix before continuing.
Question 49 of 65
What is "air brake fade"?
Correct answer: A. Loss of braking effectiveness due to overheated drums
Why: Heat-induced fade: drums and shoes lose friction.
Question 50 of 65
What is the maximum pushrod stroke for a standard size 30 chamber on a long stroke?
Correct answer: A. 2.5 inches
Why: Long-stroke 30 chambers: 2.5" maximum stroke per FMCSA inspection criteria.
Question 51 of 65
What pressure is held in the trailer air tank when the trailer is parked and disconnected?
Correct answer: A. Whatever pressure existed when uncoupled, holding spring brakes off until it leaks down
Why: When the supply line vents, spring brakes automatically apply.
Question 52 of 65
Why is it important to test the spring brakes?
Correct answer: A. Confirm they hold the vehicle and apply automatically when air is lost
Why: Brake test step: with air drained, spring brakes must apply.
Question 53 of 65
When the trailer breaks away from the tractor, the trailer brakes:
Correct answer: A. Apply automatically when air supply is lost
Why: Loss of supply line pressure causes spring/relay valve to apply trailer brakes.
Question 54 of 65
How does a tractor protection valve protect the tractor?
Correct answer: A. Closes at low pressure to keep air in tractor system if trailer breaks away
Why: Closes around 20–45 psi, isolating tractor air from a damaged trailer.
Question 55 of 65
When may you remove the wheel chocks?
Correct answer: A. After parking brake is set
Why: Set parking brake before removing chocks; chock before releasing parking brake.
Question 56 of 65
How often should the air brake system be inspected?
Correct answer: A. Pre-trip and en-route per federal rules
Why: Pre-trip and en-route inspections are mandatory.
Question 57 of 65
What is the function of the spring brakes?
Correct answer: A. Apply parking and emergency braking using mechanical spring force
Why: Powerful springs apply when air is released or lost.
Question 58 of 65
Which is true about ABS during normal stops?
Correct answer: A. Brake the same as you always have, ABS only intervenes if wheels lock
Why: No special technique required for normal stops; ABS works automatically.
Question 59 of 65
How can you tell when ABS is active?
Correct answer: A. You may feel pulsation in pedal or hear a noise
Why: Pulsing pedal/clicking noise indicates ABS modulation.
Question 60 of 65
If your ABS warning light stays on, you should:
Correct answer: A. Continue driving carefully and have it serviced — vehicle still has normal brakes
Why: Vehicle retains normal braking; arrange repair as soon as practical.
Question 61 of 65
What is the function of a quick-release valve?
Correct answer: A. Allows brakes to release quickly when pedal is released
Why: Quick-release valves vent brake-chamber air locally for fast release.
Question 62 of 65
What is the function of a relay valve?
Correct answer: A. Speeds up brake application/release on rear axles by using local air supply
Why: Relay valves reduce brake lag on long air lines.
Question 63 of 65
What is the function of the foot valve (treadle valve)?
Correct answer: A. Sends air to brake chambers in proportion to pedal pressure
Why: Foot valve modulates brake-chamber air based on pedal force.
Question 64 of 65
Which is part of an air-over-hydraulic brake system?
Correct answer: A. Air booster supplies force to a hydraulic master cylinder
Why: Air-over-hydraulic systems use air pressure to assist hydraulic brakes.
Question 65 of 65
What is "compounding" of brakes?
Correct answer: A. Applying spring brakes while service brakes are also applied — can damage system
Why: Pressing the pedal with parking brakes already applied compounds force and can damage components.