CDL Review Air Brakes 1

Oil and water usually collect in compressed air tanks. If you do not have an automatic tank drain, when should you drain the air tanks?

• After every four hours of service.

• After every working day.

• Once a week.

Answer explanation

If your vehicle does not have automatic air tank drains, drain your air tanks at the end of each working day to remove moisture and oil. Otherwise, the brakes could fail.

What is the S-cam used for?

• To release the brakes.

• To test the slack adjusters.

• To apply the brakes.

Answer explanation

When you push the brake pedal, air is let into each brake chamber. Air pressure pushes the rod out, moving the slack adjuster, thus twisting the brake camshaft. This turns the s-cam forcing the brake shoes away from one another and presses them against the inside of the brake drum.

Which of the following makes the total stopping distance for air brakes longer than that for hydraulic brakes?

• Perception distance.

• Reaction distance.

• Brake lag distance.

Answer explanation

With air brakes there is an added delay or Brake Lag. This is the time required for the brakes to work after the brake pedal is pushed. With hydraulic brake, the brakes work instantly. With air brakes it takes a little time, one half second or more, for the air to flow through the lines to the brakes.

The brake system that applies and releases the brakes when the driver uses the brake pedal is the:

• Emergency brake system.

• Service brake system.

• Parking brake system.

Answer explanation

The service brake system applies and releases the brakes when you use the brake pedal during normal driving.

To make an emergency stop with air brakes, using the stab braking method, you should:

• Pump the brake pedal rapidly and lightly.

• Brake as hard as you can, get off the brakes when the wheels lock, get back on the brakes when the wheels start rolling again.

• Brake hard until the wheels lock, and then get off the brakes for as much time as the wheels were locked.

Answer explanation

Stab braking means that you: apply your brakes all the way, and release brakes when wheels lock up. As soon as the wheels start rolling, apply the brakes fully again.

Brake lag distance at 55 mph is _____ feet?

• 50

• 32

• 23

Answer explanation

The air brake lag distance at 55 mph on dry pavement adds about 32 feet.

If your vehicle has an alcohol evaporator, it is there to:

• Rid the wet tank of alcohol that condenses and sits at the bottom.

• Eliminate the need for daily tank draining.

• Reduce the risk of ice in air brake valves in cold weather.

Answer explanation

Some air brake systems have an alcohol evaporator to put alcohol into the air system. This helps to reduce the risk of ice in air brake valves and other parts during cold weather. Daily air tank drainage is still needed to get rid of water and oil.

What can legally hold a parking or emergency brake in position for a truck, truck tractor or bus?

• Fluid pressure

• Spring pressure

• Air pressure

Answer explanation

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.

The braking power of the spring brakes:

• Increases when the service brakes are hot.

• Depends on the adjustment of the service brakes.

• Is not affected by the condition of the service brakes.

Answer explanation

The braking power of spring brakes depends on the brakes being in adjustment. If the brakes are not adjusted properly, neither the regular brakes nor the emergency/parking brakes will work right.

Which of the following should you do before leaving your vehicle unattended?

• Set the parking brakes.

• Remove the keys.

• Chock the wheels.

• Do all of the above.

Answer explanation

Never leave your vehicle unattended without applying the parking brakes or chocking the wheels. Your vehicle might roll away and cause injury and damage