CDL Air Brakes Practice Test 2026: Test de práctica 2

Test de práctica 2 de 3 de CDL Air Brakes Practice Test: 25 preguntas más con respuestas y explicaciones.

Vehículo comercial
Estados Unidos
80 preguntas
Revisado el 10 de octubre de 2026

Pregunta 1 de 25
What is a wig wag?
- A type of flashing brake light on the trailer
- A device that wags the trailer to warn drivers
- A switch that releases the spring brakes
- A metal arm that drops into view when air is low
Ver respuesta
Respuesta: D. A metal arm that drops into view when air is low
A wig wag is a low pressure warning device: a mechanical arm that drops into your view when pressure falls below 60 psi.
Pregunta 2 de 25
What does the stop light switch do in an air brake system?
- Turns on the brake lights when you brake
- Applies the spring brakes when air is low
- Stops the compressor at cut-out pressure
- Turns off the engine when pressure is low
Ver respuesta
Respuesta: A. Turns on the brake lights when you brake
An air-pressure switch turns on the brake lights when the brakes are applied.
Pregunta 3 de 25
Some older vehicles have a front brake limiting valve with a "normal" and "slippery" setting. Where should you keep it?
- It does not matter
- In the "normal" position
- In the "slippery" position at all times
- In "slippery" on dry roads only
Ver respuesta
Respuesta: B. In the "normal" position
The slippery setting cuts air to the front brakes by half, which reduces stopping power. Keep it in normal.
Pregunta 4 de 25
How are spring brakes held off during normal driving?
- By air pressure
- By the parking brake cable
- By the governor
- By hydraulic fluid
Ver respuesta
Respuesta: A. By air pressure
Spring brakes are held back by air pressure. When air is lost, the springs put on the brakes.
Pregunta 5 de 25
When will the spring brakes on a tractor or straight truck come fully on?
- When air pressure falls below 100 psi
- When air pressure falls to about 20 to 45 psi
- When air pressure rises above 125 psi
- Only when the driver pulls the yellow knob
Ver respuesta
Respuesta: B. When air pressure falls to about 20 to 45 psi
Spring brakes come fully on when air pressure drops to a range of 20 to 45 psi, typically 20 to 30 psi.
Pregunta 6 de 25
The low air pressure warning comes on while you are driving. What should you do?
- Pump the brakes to build pressure
- Speed up to charge the tanks faster
- Stop and park safely as soon as possible
- Keep driving to the next terminal
Ver respuesta
Respuesta: C. Stop and park safely as soon as possible
There may be an air leak. Controlled braking is only possible while enough air remains, so stop safely right away.
Pregunta 7 de 25
Why should you not push the brake pedal down when the spring brakes are on?
- It turns off the ABS
- The combined force can damage the brakes
- It will raise the air pressure
- It will release the spring brakes
Ver respuesta
Respuesta: B. The combined force can damage the brakes
Pushing the pedal while the spring brakes are on adds the two forces together and can damage the brakes.
Pregunta 8 de 25
What does the parking brake control look like on newer vehicles?
- A green lever beside the seat
- A red, eight-sided knob
- A blue, round push-pull knob
- A yellow, diamond-shaped knob
Ver respuesta
Respuesta: D. A yellow, diamond-shaped knob
Newer vehicles use a yellow, diamond-shaped knob. The red eight-sided knob is the trailer air supply.
Pregunta 9 de 25
How do you use the yellow parking brake knob?
- Push it in to apply; pull it out to release
- Pull it out to apply; push it in to release
- Hold it down for as long as you are parked
- Turn it to the left to apply the brakes
Ver respuesta
Respuesta: B. Pull it out to apply; push it in to release
Pull the knob out to put the parking brakes on, and push it in to release them.
Pregunta 10 de 25
What does a modulating control valve let you do?
- Drain all the air tanks from inside the cab
- Apply the spring brakes a little at a time
- Change the governor's cut-in and cut-out settings
- Turn the antilock brake system on and off
Ver respuesta
Respuesta: B. Apply the spring brakes a little at a time
A modulating control valve is a lever on the dash that lets you apply the spring brakes a little at a time.
Pregunta 11 de 25
Some vehicles have dual parking control valves with a separate small air tank. What is it for?
- Filling the tires with air when one goes low
- Giving the air horn its own supply of air
- Releasing the spring brakes briefly in an emergency
- Making the parking brakes hold more strongly
Ver respuesta
Respuesta: C. Releasing the spring brakes briefly in an emergency
The separate tank holds only enough air to release the spring brakes a few times, so plan your moves carefully.
Pregunta 12 de 25
Truck tractors with air brakes built on or after what date must have antilock brakes (ABS)?
- July 1, 2010
- January 1, 1990
- March 1, 2005
- March 1, 1997
Ver respuesta
Respuesta: D. March 1, 1997
Air-braked truck tractors built on or after March 1, 1997 must have ABS. Other air-braked vehicles built on or after March 1, 1998 must too.
Pregunta 13 de 25
Which air-braked vehicles built on or after March 1, 1998 must have ABS?
- Trucks, buses, trailers and converter dollies
- Only school buses and transit buses
- Only tank vehicles hauling hazmat
- Only truck tractors pulling trailers
Ver respuesta
Respuesta: A. Trucks, buses, trailers and converter dollies
Besides tractors (from March 1, 1997), other air brake vehicles built on or after March 1, 1998 must have antilock brakes.
Pregunta 14 de 25
What does it mean if your ABS lamp comes on for a moment when you start the vehicle and then goes out?
- The ABS has failed
- It is a normal bulb check
- The parking brake is off
- The air tanks are empty
Ver respuesta
Respuesta: B. It is a normal bulb check
Newer systems light the ABS lamp briefly at start-up as a bulb check, then turn it off.
Pregunta 15 de 25
Does ABS shorten your stopping distance?
- Yes, it always cuts stopping distance in half
- Yes, but only on dry roads
- No, it makes stopping distance much longer
- Not necessarily; it helps you keep steering control
Ver respuesta
Respuesta: D. Not necessarily; it helps you keep steering control
ABS does not change normal braking ability or always shorten stopping distance. It prevents lockup so you can steer.
Pregunta 16 de 25
In a dual air brake system, which brakes does the primary system usually run?
- The front brakes
- The rear brakes
- Only the parking brakes
- Only the trailer brakes
Ver respuesta
Respuesta: B. The rear brakes
The primary system usually works the rear axle brakes. The secondary works the front brakes and maybe one rear axle.
Pregunta 17 de 25
Before driving a vehicle with a dual air system, how much pressure should the compressor build in both systems?
- At least 150 psi
- At least 40 psi
- At least 100 psi
- At least 60 psi
Ver respuesta
Respuesta: C. At least 100 psi
Let the compressor build up at least 100 psi in both the primary and secondary systems before driving.
Pregunta 18 de 25
In a dual air system, how quickly should pressure build from 85 to 100 psi at operating rpm?
- Within about 3 minutes
- Within about 45 seconds
- Within about 5 seconds
- Within about 10 minutes
Ver respuesta
Respuesta: B. Within about 45 seconds
In dual systems, pressure should go from 85 to 100 psi within 45 seconds. Larger tanks may take longer; check the specifications.
Pregunta 19 de 25
What is the main job of the slack adjuster?
- It tells the compressor when to pump
- It drains water from the air tanks
- It turns on the brake lights when braking
- It links the push rod to the brake camshaft
Ver respuesta
Respuesta: D. It links the push rod to the brake camshaft
The push rod turns the slack adjuster, which turns the camshaft and S-cam to apply the brakes.
Pregunta 20 de 25
You pull hard on a slack adjuster with the brakes released. How far can it move before it probably needs adjusting?
- It should never move at all, even slightly
- About one inch where the push rod attaches
- About one-eighth inch at the end of the arm
- About six inches at the end of the arm
Ver respuesta
Respuesta: B. About one inch where the push rod attaches
If a slack adjuster moves more than about one inch where the push rod attaches, it probably needs adjustment.
Pregunta 21 de 25
What must you do before checking slack adjusters?
- Set the parking brakes and run the engine
- Raise the vehicle on a jack so wheels turn
- Drain the air tanks completely first
- Chock the wheels and release the parking brakes
Ver respuesta
Respuesta: D. Chock the wheels and release the parking brakes
To check slack adjusters you must release the parking brakes, so chock the wheels first on level ground.
Pregunta 22 de 25
What is the most common problem found in roadside inspections of air brakes?
- Missing reflective triangles
- Brakes out of adjustment
- Empty alcohol evaporators
- Broken brake lights
Ver respuesta
Respuesta: B. Brakes out of adjustment
Out-of-adjustment brakes are the number one problem inspectors find.
Pregunta 23 de 25
Your vehicle has automatic slack adjusters. Do they still need to be checked?
- No, they adjust themselves
- Only once a year at service
- Yes, during every inspection
- Only after a crash or a fault
Ver respuesta
Respuesta: C. Yes, during every inspection
Vehicles built since 1994 have automatic slack adjusters, but they must still be checked.
Pregunta 24 de 25
An automatic slack adjuster is out of adjustment. What does this usually mean?
- There is probably a mechanical problem that needs repair
- The tanks need draining
- The governor is set too high
- It just needs a quick manual adjustment and no repair
Ver respuesta
Respuesta: A. There is probably a mechanical problem that needs repair
Manual adjustment of an automatic adjuster is only a temporary emergency fix. Have the vehicle repaired as soon as possible.
Pregunta 25 de 25
How long can a crack in a brake drum be?
- Any length, as long as it is not leaking
- Up to the full width of the friction area
- Up to half the width of the friction area
- Up to 6 inches, measured along the drum
Ver respuesta
Respuesta: C. Up to half the width of the friction area
Drum cracks must not be longer than one-half the width of the friction area.

Exámenes relacionados