CDL Practice Test

CDL Braking Systems Practice Questions

Braking Systems makes up 5 of every 50 questions on a Tigertest CDL practice test. Here are 10 of the 50 questions on it, each with the answer and the reason.

Updated 2026-11-10 by the Tigertest team. Covers the CDL general knowledge exam. 80% to pass on the real test.

1. 1. What is the main difference between hydraulic and air brake systems?

   • A.Air brakes use brake fluid instead of compressed air
   • B.Hydraulic brakes use brake fluid, air brakes use compressed air
   • C.There is no significant difference between these systems
   • D.Hydraulic brakes use compressed air for power assistance

   Answer: B. Hydraulic brake systems use brake fluid to transfer force, while air brake systems use compressed air to operate the brakes.

2. 2. What happens when an S-cam brake is applied?

   • A.The brake pad compresses against the rotor
   • B.Air pressure decreases in the brake chamber
   • C.The wedge pushes outward against the shoes
   • D.The S-cam rotates and pushes the brake shoes outward

   Answer: D. In S-cam brakes, when air pressure is applied, the pushrod moves the slack adjuster, which rotates the S-cam that pushes the brake shoes outward against the drum.

3. 3. What is brake fade and what causes it?

   • A.Loss of braking power due to overheating
   • B.Increased braking power from cold weather
   • C.Normal wear on brake pads
   • D.Air pressure loss in the system

   Answer: A. Brake fade occurs when brakes overheat from excessive use, causing reduced friction between brake components and decreased stopping power.

4. 4. How do automatic slack adjusters maintain proper brake adjustment?

   • A.They adjust only when the vehicle is parked overnight
   • B.They work only when the vehicle is backing up
   • C.They automatically adjust during normal brake use
   • D.They require daily manual adjustment

   Answer: C. Automatic slack adjusters continuously monitor and maintain proper brake shoe-to-drum clearance during normal brake applications, reducing maintenance requirements.

5. 5. What happens to brake drums when they become overheated from excessive braking?

   • A.They maintain their normal shape and function
   • B.They become more responsive to light pedal pressure
   • C.They expand and the brake shoes contact less surface area
   • D.They contract and grip the brake shoes tighter

   Answer: C. Overheated brake drums expand outward, moving away from the brake shoes. This reduces contact area and braking force, contributing to brake fade.

6. 6. What is the proper technique for controlled braking?

   • A.Apply firm, steady pressure without locking wheels
   • B.Pump the brakes rapidly in short quick bursts
   • C.Apply maximum pressure immediately for fastest stopping
   • D.Use only the parking brake for emergency situations

   Answer: A. Controlled braking involves applying firm, steady pressure to the brake pedal while maintaining steering control and avoiding wheel lockup.

7. 7. When should you use stab braking technique?

   • A.During normal daily driving
   • B.When parking the vehicle
   • C.Only in wet conditions
   • D.Only when ABS is not working

   Answer: D. Stab braking (apply full pressure, release when wheels lock, repeat) should only be used on vehicles without ABS or when ABS has failed.

8. 8. What happens to air brakes when water gets into the system?

   • A.Nothing changes in the brake system operation
   • B.Water can freeze and cause brake failure
   • C.The air compressor works harder but brakes improve
   • D.They work more efficiently due to liquid pressure

   Answer: B. Water in air brake systems can freeze in cold weather, blocking air lines and preventing proper brake operation, potentially causing complete brake failure.

9. 9. What is brake lag in air brake systems?

   • A.Permanent brake failure that requires immediate repair
   • B.Time delay between applying brakes and full effectiveness
   • C.Brakes that work too well and cause skidding
   • D.Loss of air pressure during normal operation

   Answer: B. Brake lag is the time delay between when you push the brake pedal and when the air brakes reach full effectiveness, typically about half a second.

10. 10. How do spring brakes work when parking?

    • A.They use hydraulic pressure to engage parking position
    • B.They require electrical power to function during parking
    • C.They work only when the vehicle is moving
    • D.Springs apply brakes when air pressure is released

    Answer: D. Spring brakes are held off by air pressure during normal operation, but powerful springs automatically apply the brakes when air pressure drops or is released for parking.