TruckingTruth logo

Air Brakes Free CDL Practice Tests
Page 2

Prepare For The Air Brakes Portion Of Your CDL Written Exams

Air Brakes Questions

Click On The Picture To Begin

Good Luck!

To stop the vehicle, the brake shoes and linings are pushed against:
  • The tire
  • The brake chamber
  • The brake drum
  • The slack adjuster
Click here to look up the answer

From The CDL Manual

The S-cam forces the brake shoes away from one another and presses them against the inside of the brake drum. When you release the brake pedal, the S-cam rotates back, and a spring pulls the brake shoes away from the drum, letting the wheels roll freely again.

Next
In order to make contact with the brake drum, the brake pads and linings are pushed outward by the:
  • Push-rod
  • S-cam
  • Slack adjuster
  • Brake pedal
Click here to look up the answer

From The CDL Manual

S-cam brakes:

When you push the brake pedal, air is let into each brake chamber (see Figure 5-2). Air pressure pushes the rod out, moving the slack adjuster, thus twisting the brake cam shaft. This turns the S-cam (named because it is shaped like the letter S). The S-cam forces the brake shoes away from one another and presses them against the inside of the brake drum. When you release the brake pedal, the S-cam rotates back, and a spring pulls the brake shoes away from the drum, letting the wheels roll freely again.

Prev
Next
What type of brakes pushes a wedge between the ends of two brake shoes to stop the vehicle?
  • Wedge brakes
  • Disc brakes
  • Spring brakes
  • S-cam brakes
Click here to look up the answer

From The CDL Manual

Wedge brakes:

In these types of brakes, the brake chamber push rod pushes a wedge directly between the ends of two brake shoes. This shoves them apart and against the inside of the brake drum. Wedge brakes may have a single brake chamber or two brake chambers, pushing wedges in at both ends of the brake shoes. Wedge-type brakes may be self-adjusting or may require manual adjustment.

Prev
Next
The type of brakes that clamp the rotor between the brake shoes is:
  • Wedge brakes
  • Foundation brakes
  • S-cam brakes
  • Disc brakes
Click here to look up the answer

From The CDL Manual

Disc brakes:

In air-operated disc brakes, air pressure acts on a brake chamber and slack adjuster, like S-cam brakes. But instead of the S-cam, a “power screw” is used. The pressure of the brake chamber on the slack adjuster turns the power screw. The power screw clamps the disc or rotor between the brake lining pads of a caliper, similar to a large C-clamp.

Prev
Next
Why is manually adjusting automatic slack adjusters dangerous?
  • There is no reason not to manually adjust them
  • It could start a fire
  • It gives the vehicle operator a false sense of security about the effectiveness of the braking system.
  • It could explode in your face
Click here to look up the answer

From The CDL Manual

The manual adjustment of automatic slack adjusters is dangerous because it gives the vehicle operator a false sense of security about the effectiveness of the braking system.

Prev
Next
What tells the driver how much air pressure is in the air tanks?
  • Front brake limiting valve
  • Supply pressure gauge
  • Low air-pressure gauge
  • Application pressure gauge
Click here to look up the answer

From The CDL Manual

Supply Pressure Gauges —

All air-brake vehicles have a pressure gauge connected to the air tank. If the vehicle has a dual air brake system, there will be a gauge for each half of the system (or a single gauge with two needles). Dual systems are discussed on page 65. These gauges tell you how much pressure is in the air tanks.

Prev
Next
While applying the brakes, what tells the driver how much air pressure is being used?
  • Low air pressure gauge
  • Supply pressure gauge
  • Application pressure gauge
  • Front brake limiting valve
Click here to look up the answer

From The CDL Manual

Application Pressure Gauge —

This gauge shows how much air pressure you are applying to the brakes. (This gauge is not on all vehicles.) Increasing application pressure to hold the same speed means the brakes are fading. You should slow down and use a lower gear. The need for increased pressure also can be caused by brakes out of adjustment, air leaks or mechanical problems.

Prev
Next
Required on all vehicles with air brakes, what tells the driver that air pressure is too low?
  • Supply pressure gauge
  • Low air pressure gauge
  • Application pressure gauge
  • Front brake limiting valve
Click here to look up the answer

From The CDL Manual

Low Air-Pressure Gauge —

A low air-pressure warning signal is required on vehicles with air brakes. A warning signal you can see must come on before the air pressure in the tanks falls below 60 psi (or one-half the compressor governor cutout pressure on older vehicles). The warning is usually a red light. A buzzer also may come on.

Prev
Next
A mechanical device that drops a low air warning into a drivers view is called a:
  • Wig wag
  • Zim zam
  • Flim flam
  • Jig jag
Click here to look up the answer

From The CDL Manual

Another type of warning is the “wig wag.” This device drops a mechanical arm into your view when the pressure in the system drops below 60 psi. An automatic wig wag will rise out of your view when the pressure in the system goes above 60 psi. The manual reset type must be placed in the “out of view” position manually. It will not stay in place until the pressure in the system is above 60 psi.

Prev
Next
At what level will the low air warning usually take effect?
  • 85 psi
  • 75 psi
  • 60 psi
  • 100 psi
Click here to look up the answer

From The CDL Manual

Low Air-Pressure Gauge —

A low air-pressure warning signal is required on vehicles with air brakes. A warning signal you can see must come on before the air pressure in the tanks falls below 60 psi (or one-half the compressor governor cutout pressure on older vehicles). The warning is usually a red light. A buzzer also may come on.

Prev
Finish
Please select an option
[3,2,1,4,3,2,3,2,1,3]
10

Join Us!

We have an awesome set of tools that will help you understand the trucking industry and prepare for a great start to your trucking career. Not only that, but everything we offer here at TruckingTruth is 100% free - no strings attached! Sign up now and get instant access to our member's section:
High Road Training Program Logo
  • The High Road Training Program
  • The High Road Article Series
  • The Friendliest Trucker's Forum Ever!
  • Private messaging for more personal questions
  • Email Updates When New Articles Are Posted

About Us

TruckingTruth was founded by Brett Aquila (that's me!), a 15 year truck driving veteran, in January 2007. After 15 years on the road I wanted to help people understand the trucking industry and everything that came with the career and lifestyle of an over the road trucker. We'll help you make the right choices and prepare for a great start to your trucking career.

Read More

Becoming A Truck Driver

Becoming A Truck Driver is a dream we've all pondered at some point in our lives. We've all wondered if the adventure and challenges of life on the open road would suit us better than the ordinary day to day lives we've always known. At TruckingTruth we'll help you decide if trucking is right for you and help you get your career off to a great start.

Learn More