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Maryland CDL DMV Air Brakes 1

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1. To inspect slack adjusters on S-cam brakes, you need to:
Park on a hill and test the brakes.
Put on gloves and push in the slack adjusters.
Remove the drum and look inside.
Chock the wheels and disengage the parking brake.

Check each slack adjuster after parking on level ground, setting wheel chocks, and disengaging the parking brake. Pull the slack adjusters to make sure they do not move more than about one inch from where the push rod is attached. If they move more than one inch, they may be out of adjustment and will need to be fixed.

2. Failing to drain the tanks in an air brake system can result in:
Water freezing and causing brake failure.
Squishy brakes.
Too much air collecting.
Too much fuel being carried.

In an air brake system, the air storage tanks must be drained to remove accumulated water and compressor oil. Failing to do this can cause damage. For example, water that has built up in the system could freeze in cold weather and cause brake failure.

3. When leaving your vehicle unattended:
The parking brake should be used.
The parking brake only needs to be used if the vehicle is parked on a slope.
The parking brake should not be used, as it can damage the tires.

In general, you should always use the parking brake when parking your vehicle. However, you should not apply the parking brake if your brakes are very hot or if your brakes are wet and temperatures are below freezing.

4. What is brake lag?
The time required for the brakes to work after the brake pedal is pressed
The distance between the brake pedal and the floor
The amount of air pressure used to stop the vehicle

Because air takes time to flow through the air lines to the brakes, air brakes cannot begin working instantly. There is often a brake lag of at least one-half of a second between the moment the brake pedal is pressed and the moment the brakes begin to work.

5. An air compressor governor will stop the compressor from pumping air once the air tanks have an air pressure level of:
125 psi.
100 psi.
150 psi.
80 psi.

An air compressor governor will stop the compressor from pumping air once the air tanks are at an air pressure level of 125 psi. This air pressure level is referred to as the "cut-out" level.

6. Having ABS on only one axle:
Can be dangerous.
Still allows you additional control when braking.
Slows the vehicle, but cannot stop it.

If you have an Anti-Lock Braking System (ABS) equipped on only the tractor, only the trailer, or only one axle, you will still have more control over the vehicle when braking than you would without ABS. You should brake normally.

7. To make a stop in a vehicle using air brakes, the driver should:
Press down the brake pedal.
Lift the brake pedal toward them.
Push in the brake knob.
Pull out the brake knob.

To make a normal stop in an air-braked vehicle, push the brake pedal down and control the pressure so that the vehicle comes to a smooth, safe stop.

8. What must be on an air tank in an air-braked vehicle?
A check valve
A lock
A trap door
An oxidizer

All air tanks on air-braked vehicles must have one-way check valves located between the air compressor and the first reservoir. This prevents air from flowing out in the event of a leak.

9. On newer vehicles, how do you put on the parking brake?
Move a lever to the right.
Push in the yellow, diamond-shaped knob.
Pull out the yellow, diamond-shaped knob.
Pull up on the steering column.

On newer vehicles with air brakes, the parking brake is controlled by a yellow, diamond-shaped knob. The knob is pulled out to set the brakes, and pushed in to release them.

10. An Anti-Lock Braking System (ABS):
Is not available for vehicles with air brakes.
Is not helpful in most driving situations.
Can help you maintain control when braking.

Anti-Lock Braking Systems (ABS) are compatible with air brakes and help a driver maintain control of their vehicle by preventing wheel lockup.

11. An emergency brake must be controlled by:
Mechanical force.
Air pressure.

All trucks, truck tractors, and buses must be equipped with emergency brakes and parking brakes. Because air pressure can eventually leak away, emergency and parking brakes should be held on by mechanical force.

12. The emergency brake system uses:
Only parts of the parking brake system.
Only parts of the service brake system.
Parts of both the parking and service brake systems.
Only parts unique to the emergency brake system.

In an air brake system, there are three different braking systems: a service brake system, a parking brake system, and an emergency brake system. The emergency brake system uses parts of both the parking and service brake systems.

13. In a vehicle with dual air brakes, what happens if one system is low on pressure?
The air from the other system will be used to supplement the system with the low pressure.
The front or rear brakes may not work properly.
All brakes will be inoperable.
The low system will use an auxiliary system to fill the tank.

In a dual air brake system, if one of the air systems gets very low on pressure, either the front or rear brakes will not be operating fully. You should bring your vehicle to a safe stop and have the air system repaired.

14. In a dual air brake system, a leak in one system:
Always means there are leaks in both systems.
May not affect the other system.
Is not something to worry about.
Will also affect the other system.

A dual air brake system is made up of two separate air brake systems. If there is an air leak in one system, it may not affect the other.

15. What should happen if the air pressure in the air brake system tanks falls below 60 psi?
A warning light should come on.
Lights should flash on the outside of the vehicle.
A message should appear on the control panel.
The vehicle should stop.

On vehicles with air brakes, a low air pressure warning signal will come on if the pressure in the air tanks falls below 60 psi. On large buses, the signal may activate at 80 to 85 psi.

16. An air brake-equipped vehicle traveling at a speed of 55 mph under ideal driving conditions will need approximately ____ to come to a complete stop.
100 feet
250 feet
300 feet
450 feet

A vehicle's total stopping distance is made up of perception distance, reaction distance, brake lag distance, and braking distance. With all of these factors included, an air brake-equipped vehicle traveling at a speed of 55 mph under ideal driving conditions will need approximately 450 feet to come to a complete stop.

17. If the spring brakes are activated, you should never:
Push down the brake pedal.
Open the hood.
Release air from the air storage tanks.
Open the door to the cab.

Never apply the brake pedal if your spring breaks are activated. Brakes can be damaged if they are subject to both springs and air pressure.

18. When traveling down a steep downgrade:
The air brakes should be used.
Shift into a lower gear, then use brakes to supplement the braking effect of the engine.
The vehicle should be continually downshifted in the place of using the brakes.
The vehicle should be driven on the shoulder.

On a downgrade, the braking effect of the engine should be your primary method of controlling speed. Shift down to a lower gear before starting down the hill and save the brakes for additional slowing or stopping that may be required by road or traffic conditions.

19. Using an Anti-Lock Braking System (ABS):
Is required in some states.
Shortens brake response time.
Provides additional control.

An Anti-Lock Braking System (ABS) helps to provide additional control during hard braking, but does not necessarily shorten a vehicle's stopping distance.

20. If the brake pads rub against the brake drums and create too much heat:
The brakes will stick.
The brakes will become extra sensitive.
The brakes may stop working.
The air compressor will kick on to cool the brakes.

Brakes heat up with use. If they are overused and become too hot, expansion and chemical changes will make them less effective and eventually cause them to stop working altogether. This is known as "brake fade."

21. When about to drive a vehicle with a dual brake system, a driver should:
Let the vehicle warm up to ensure the fuel reaches the engine.
Wait for air pressure to build in both the primary and secondary systems.
Begin driving just after the engine starts.
Pump the pedal about 20 times to build pressure, then begin driving.

Before driving a vehicle with a dual air brake system, allow time for the compressor to build up pressure to at least 100 psi in both systems.

22. What do the two systems of a dual air brake system share?
An air compressor
Air tanks

Both systems in a dual air brake systems share a single air compressor. If the air compressor is damaged, neither system will be able to operate properly.

23. Air brakes use ____ to function.
Compressed air
Liquid nitrogen
Carbon dioxide

The brakes in an air brake system use compressed air to function properly.

24. You should not use the parking brake:
If your vehicle is stopped on a level surface.
If your vehicle is stopped on a slight incline.
If your vehicle's brakes are very hot.
If your vehicle's other braking systems seem to be working adequately.

A parking brake should not be used if the vehicle's brakes are very hot from use on a steep downgrade or if the brakes are very wet and temperatures are freezing. Using the parking brake when brakes are hot could cause damage to the brakes, and using the brakes when they are wet in freezing weather may cause the brakes to ice up, rendering the vehicle immobile.

25. To use the stab braking method, you should:
Apply the brakes completely until the wheels lock up, release the brakes until the wheels start rolling, then repeat the process.
Apply the brakes about halfway, but allow the wheels to keep rolling.
Apply the brakes completely until the wheels lock up and the vehicle stops.
Apply the emergency brake until the vehicle starts to slow.

The stab braking method for emergency stops involves fully applying the brakes until they lock up. The brakes are then released until the wheels start rolling, and then the process is repeated.

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