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Air Brakes Free CDL Practice Tests
Page 3

Prepare For The Air Brakes Portion Of Your CDL Written Exams

Air Brakes Questions

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Good Luck!

A warning to drivers behind you that the air brakes have been applied is the:
  • Low air warning gauge
  • Stop light switch
  • Brake siren
  • Smoke screen
Click here to look up the answer

From The CDL Manual

Stop Light Switch —

Drivers behind you must be warned when you put your brakes on. The air brake system does this with an electric switch that works by air pressure. The switch turns on the brake lights when you put on the air brakes.

Next
A device that limits the amount of air provided to the front brakes is a:
  • Dual parking control valve
  • Modulating control valve
  • Supply pressure valve
  • Front brake limiting valve
Click here to look up the answer

From The CDL Manual

Front Brake Limiting Valve —

Some older vehicles (made before 1975) have a front brake limiting valve and a control in the cab. The control is usually marked “normal” and “slippery.” When you put the control in the “slippery” position, the limiting valve cuts the “normal” air pressure to the front brakes by half. Limiting valves were used to reduce the chance of the front wheels skidding on slippery surfaces. However, they actually reduce the stopping power of the vehicle. Front-wheel braking is good under all conditions. Tests show that front-wheel skids from braking are not likely even on ice. Make sure the control is in the “normal” position to have normal stopping power.

Many vehicles have automatic front-wheel limiting valves. They reduce the air to the front brakes except when the brakes are put on very hard (60 psi or more application pressure). These valves cannot be controlled by the driver.

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Next
When driving an older vehicle that has a manual front brake limiting valve, drivers should:
  • Keep the control in "normal" position
  • Drive less than 55 mph
  • Not even drive that vehicle
  • Use it only in slippery weather
Click here to look up the answer

From The CDL Manual

Front Brake Limiting Valve —

Tests show that front-wheel skids from braking are not likely even on ice. Make sure the control is in the “normal” position to have normal stopping power.

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Next
Spring brakes are applied:
  • When driving on ice
  • When air pressure is normal
  • When service brakes are applied
  • When air pressure drops to very low levels
Click here to look up the answer

From The CDL Manual

Tractor and straight truck spring brakes will come on fully when air pressure drops to a range of 20 to 45 psi (typically 20 to 30 psi). Do not wait for the brakes to come on automatically. When the low air-pressure warning light and buzzer first come on, bring the vehicle to a safe stop right away while you can still control the brakes.

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Next
In case of air pressure loss, a mechanical means of preventing the vehicle from moving is called:
  • S-cam brakes
  • Spring brakes
  • Primary brakes
  • Foundation brakes
Click here to look up the answer

From The CDL Manual

Spring Brakes —

All trucks, truck tractors and buses must be equipped with emergency brakes and parking brakes. They must be held on by mechanical force because air pressure can eventually leak away. Spring brakes are usually used to meet these needs. When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes. A parking brake control in the cab allows the driver to let the air out of the spring brakes. This lets the springs put the brakes on. A leak in the air brake system, which causes all the air to be lost, will also cause the springs to put on the brakes.

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Next
Spring brakes will generally come on at:
  • 60 psi
  • 20-45 psi
  • 80 psi
  • 120 psi
Click here to look up the answer

From The CDL Manual

Tractor and straight truck spring brakes will come on fully when air pressure drops to a range of 20 to 45 psi (typically 20 to 30 psi). Do not wait for the brakes to come on automatically. When the low air-pressure warning light and buzzer first come on, bring the vehicle to a safe stop right away while you can still control the brakes.

Prev
Next
Spring brakes will come on automatically, but the parking brake can also be applied:
  • By stomping on the brake pedal
  • With an in-cab control
  • Only while stopped
  • By getting out and adjusting the brakes
Click here to look up the answer

From The CDL Manual

A parking brake control in the cab allows the driver to let the air out of the spring brakes. This lets the springs put the brakes on.

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Next
If the low air warning comes on while you are driving, you should:
  • Bring the vehicle to a safe stop right away while you can still control the brakes
  • Immediately start pumping the brakes
  • Activate the emergency brake
  • Activate the parking brake, and grip the steering wheel very tightly
Click here to look up the answer

From The CDL Manual

Tractor and straight truck spring brakes will come on fully when air pressure drops to a range of 20 to 45 psi (typically 20 to 30 psi). Do not wait for the brakes to come on automatically. When the low air-pressure warning light and buzzer first come on, bring the vehicle to a safe stop right away while you can still control the brakes.

Prev
Next
In most newer vehicles, the parking brake control will be:
  • Yellow and diamond-shaped
  • Red and round
  • Inaccessible to the driver
  • Mounted on the reservoir
Click here to look up the answer

From The CDL Manual

Parking Brake Controls —

In newer vehicles with air brakes, you apply the parking brakes using a diamondshaped, yellow, push-pull control knob. You pull the knob out to put the parking brakes (spring brakes) on, and push it in to release them. On older vehicles, the parking brakes may be controlled by a lever. Use the parking brakes whenever you park.

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Next
To avoid damaging the brakes, what should you never do while the spring brakes are applied?
  • Exit the vehicle
  • Start the vehicle
  • Push the brake pedal
  • Put the vehicle in gear
Click here to look up the answer

From The CDL Manual

Caution:

Never push the brake pedal down when the spring brakes are on. If you do, the brakes could be damaged by the combined forces of the springs and the air pressure. Many brake systems are designed so this will not happen. But not all systems are set up that way, and those that are may not always work. It is much better to develop the habit of not pushing the brake pedal down when the spring brakes are on.

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