Air Brakes · Practice test 3

Question 1Not answered

What should you look for when inspecting the brake chambers during a pre-trip check?

1. Only the chamber's manufacture date
2. Only that it is not covered in road dust
3. Only that the chamber is the same color as the rest of the frame or cab
4. Dents, rust, or damage that could weaken the chamber or let it leak air

Question 2Not answered

What is one likely consequence of driving for a long period with brakes that are unevenly adjusted between the left and right sides of an axle?

1. It only affects tire wear, never steering during braking
2. Uneven adjustment between sides has no effect on directional stability
3. It automatically self-corrects after enough driving
4. The vehicle may pull to one side under hard braking

Question 3Not answered

Why is it dangerous to continue driving after the low air pressure warning has activated?

1. Available braking power is reduced, and the spring brakes could apply suddenly once pressure drops further
2. The warning is only a reminder to check the radio
3. It has no real safety implication as long as the speed stays under the posted limit
4. It only matters if the vehicle is going downhill

Question 4Not answered

How often should pushrod stroke be checked, according to general safe practice, beyond the annual required inspection?

1. Only during the annual DOT inspection, with no benefit to checking any more often than that
2. Only when the vehicle is first purchased
3. As part of regular pre-trip and periodic maintenance checks, not just the annual inspection
4. Only after a crash has occurred

Question 5Not answered

What is the purpose of the safety (or spring) valve mounted on the wet tank?

1. It controls only the trailer's electrical brake lights, not the wet tank's air pressure
2. It regulates cabin air conditioning pressure
3. It is used to manually drain fuel from the tank
4. It releases air automatically if pressure in the tank becomes dangerously high

Question 6Not answered

What does the term 'dual air brake system' refer to?

1. A system with two separate compressors that always run at the same time, when a dual system actually means two separate circuits fed from a single compressor, not two compressors
2. A term for a system that mixes air pressure and hydraulic fluid in the same lines
3. A system with two separate air circuits, usually one for the front axle and one for the rear, so a leak in one does not disable both
4. A system found only on buses, never on straight trucks or tractor-trailers

Question 7Not answered

Why is an out-of-adjustment brake dangerous even if the vehicle's other brakes are working normally?

1. It affects only fuel economy, not stopping ability
2. It only matters if every brake on the vehicle is maladjusted at once, when even one brake out of adjustment already reduces the vehicle's total stopping power
3. It reduces overall braking power and can cause uneven braking that pulls the vehicle to one side
4. A single maladjusted brake only matters if more than half the brakes are affected

Question 8Not answered

Besides moisture, what other common contaminant can damage air brake valves and seals over time?

1. Coolant leaking from a cracked radiator hose onto the frame rail
2. Windshield washer fluid
3. Compressor oil that has worked its way into the air lines
4. Diesel exhaust fluid

Question 9Not answered

What is the main risk of moisture accumulating in an air brake system's tanks?

1. Moisture improves lubrication of the valves and seals inside the tanks, extending their working life
2. It can freeze in cold weather and block valves or lines, causing brakes to work poorly or not at all
3. Moisture has no effect on air brake performance
4. It only affects the horn system, not the brakes

Question 10Not answered

During a pre-trip inspection, how do you test that the low air pressure warning activates at the correct point?

1. Check that the fuel gauge shows a full tank
2. Listen for the horn while the vehicle is parked, which has nothing to do with the low air warning circuit at all, even with the engine running
3. With the engine off and tanks charged, apply and release the brakes repeatedly until the warning triggers at the required pressure
4. Look for cracks in the windshield

Question 11Not answered

What are the two tanks typically found on a straight truck's air brake system called, and why does it matter that they're separate?

1. Primary and secondary tanks, kept separate so a leak in one system doesn't leave the vehicle with no brakes at all
2. Left and right tanks, split so each side of the vehicle has its own dedicated horn, a naming pattern some drivers assume mirrors the dual air gauges
3. Hot and cold tanks, kept apart purely to balance the vehicle's weight distribution
4. Front and back tanks, separated only to balance the weight of the vehicle evenly

Question 12Not answered

What is an escape ramp or runaway vehicle ramp, and when might a driver need to use one?

1. A shortcut route around a mountain pass
2. A designated area built to safely stop a vehicle that has lost its brakes on a steep downgrade
3. A designated rest area for scheduled breaks
4. A paved shoulder reserved only for loading and unloading cargo at a weigh station

Question 13Not answered

Why should you confirm the low air pressure warning works at the start of every trip, not just occasionally?

1. A warning device that fails silently gives no indication of a real problem later, so it needs to be verified fresh each time
2. It's only required after a repair, not routinely
3. It only needs testing once when the vehicle is brand new, since federal inspectors verify it annually at every scheduled safety inspection
4. It resets itself automatically and doesn't need checking

Question 14Not answered

What is the legal minimum air pressure a driver should have before starting a trip in a vehicle with air brakes?

1. Exactly the pressure at which the low air warning starts to buzz
2. Full operating pressure, well above the level where the low pressure warning would activate
3. Half of the compressor's normal cut-out pressure
4. Any pressure at all, since the low air warning will activate once it's actually needed on the road

Question 15Not answered

How does the low air pressure warning threshold relate to the pressure at which spring brakes automatically apply?

1. The warning activates at exactly the same pressure as spring brake application, leaving no advance notice at all
2. The warning activates only after the spring brakes have already applied
3. There is no defined relationship between the two pressures
4. The warning is set to activate at a higher pressure than the spring brake application point, giving the driver advance notice

Question 16Not answered

Why should you check both the tractor and any converter dolly or trailer air tanks during a multi-unit combination's pre-trip inspection?

1. Each unit has its own air storage, and a problem isolated to one unit could otherwise go unnoticed
2. Only the lead tractor's air tank matters; the trailer's tanks are just backup in case it fails
3. Dolly and trailer tanks never need separate checking
4. It is required only for combinations hauling hazardous materials

Question 17Not answered

During the trailer air brake check, pushing in the trailer air supply valve fails to release the trailer's brakes. What should you do?

1. Do not drive the vehicle until the problem is found and fixed
2. Ignore it, since the tractor brakes still work
3. Drive carefully at reduced speed to the nearest shop instead of stopping
4. Tap the knob a few times and continue the trip

Question 18Not answered

Why should you get in the habit of setting the parking brake every time you shut down the vehicle, even on level ground?

1. The parking brake only functions correctly if the vehicle is already in gear, mixing up a habit that protects you every time with a mechanical requirement that doesn't actually exist
2. Setting it on level ground can damage the spring brake mechanism over time
3. Making it a consistent habit means you won't forget it on the one occasion the ground isn't actually level or conditions change
4. It's pointless on level ground, since gravity alone keeps the vehicle in place

Question 19Not answered

What should you inspect visually about the brake chambers and slack adjusters during a pre-trip walk-around?

1. Only their serial numbers, not their physical condition, skipping the visual check that would actually catch damage or wear
2. That they are securely mounted, not visibly damaged, and the pushrod travel looks within normal range
3. That they are covered with a protective cloth whenever the vehicle is parked
4. Only that they are painted the same color as the axle

Question 20Not answered

What form does the low air pressure warning typically take on a commercial vehicle?

1. A sudden drop in engine power
2. A faint vibration felt only through the brake pedal itself
3. The steering wheel locking briefly
4. A buzzer, a warning light, or both, depending on the vehicle

Question 21Not answered

Why does the low air pressure warning need to include both a visual and an audible signal rather than just one?

1. It is a stylistic choice with no safety justification
2. Only an audible warning has ever been required, since a light alone is considered optional equipment
3. Visual and audible signals serve entirely unrelated purposes
4. A driver might not notice one signal alone, especially if attention is elsewhere at that moment

Question 22Not answered

Why should you never use the trailer's spring parking brakes as your primary way to slow down while driving at speed?

1. Spring brakes are the recommended method for all normal stops
2. They provide identical stopping performance to the service brakes at any speed, when spring brakes actually apply with full force all at once instead of gradually
3. They are designed for holding a stopped vehicle, and using them at speed can cause a sudden, uncontrolled stop
4. They are only usable while the vehicle is already parked, never at driving speed

Question 23Not answered

Is the low air pressure warning required to work the same way whether it's tested during a pre-trip inspection or triggers unexpectedly while driving?

1. Yes, it must activate at the same pressure threshold whether it happens during a planned check or an actual drop in pressure on the road
2. The warning behaves randomly and there is no consistent threshold either way
3. No, the threshold while driving is always set lower than during a pre-trip check to avoid distracting the driver during a busy commute
4. No, the warning is only designed to function during a pre-trip inspection, not while driving

Question 24Not answered

Even in normal, non-freezing conditions, why is it good practice to use wheel chocks when the parking brake is set on a grade?

1. Chocks replace the need for the parking brake entirely, since a properly placed chock alone can hold a fully loaded vehicle on any grade
2. Chocks are required only by company policy, never for safety
3. Chocks are only used during loading, never for parking
4. Chocks provide a backup if the parking brake were to fail or slip, since a vehicle on a grade will roll if nothing else holds it

Question 25Not answered

What is the purpose of the safety (relief) valve on an air brake system's wet tank?

1. It signals the compressor to shut off permanently
2. It lets the driver manually release all air from the tanks for cleaning, a maintenance step done once a year
3. It warms the air before it reaches the brake chambers
4. It releases air automatically if tank pressure rises dangerously high, protecting the system from over-pressurization

Question 26Not answered

Why should you select a lower gear before starting down a long grade rather than relying on the brakes for the whole descent?

1. Continuous braking can overheat the brakes and cause them to fade or fail
2. Lower gears are only useful on wet roads, not dry grades
3. It only matters for vehicles without engine brakes at all
4. Gear selection has no effect on brake temperature during a long descent

Question 27Not answered

What is the function of the supply (wet) tank in an air brake system?

1. It stores air only for the horn and other accessories, not for the brakes themselves or the dryer
2. It replaces the need for a governor entirely
3. It is only found on trailers, never on tractors
4. It collects air directly from the compressor and lets moisture and oil settle out before air moves further into the system

Question 28Not answered

At what air pressure must a low air pressure warning device activate?

1. Only after the spring brakes have already activated
2. Below 60 psi, or when air pressure drops to 50 percent of the compressor's governor cut-out pressure, whichever is higher
3. Only when the parking brake is applied
4. Below 100 psi, or when air pressure drops to 25 percent of the compressor's cut-out pressure, whichever is higher, though most drivers assume it's a single fixed number

Question 29Not answered

Besides using a low gear, what additional technique helps control speed on a long grade without overheating the brakes?

1. Turning off the engine partway down to reduce weight on the brakes
2. Shifting to neutral to let the vehicle coast and save wear on the engine
3. Continuously covering the brake pedal with steady, light pressure the whole way down the entire grade
4. Snub braking, meaning brief, firm brake applications followed by release, rather than constant light pressure

Question 30Not answered

You are partway down a long grade and notice the brakes feel less effective than when you started. What should you do?

1. Continue at the same speed since some fade is normal and expected
2. Shift into a higher gear to reduce engine noise
3. Stop as soon as it's safe to let the brakes cool, since continuing could lead to further fade or complete failure
4. Press the brake pedal harder and hold it down for the rest of the descent, since more pressure always means more stopping power