Commercial Driver’s License (CDL) Air Brakes Endorsement Study Guide

The Air Brakes Endorsement is required if you plan to drive a vehicle equipped with air brakes. Below is a comprehensive study guide that will assist you in preparing for this endorsement.

1. Basic Air Brake System Principles​

Understanding Air Brakes

Air brakes use compressed air to make the brakes work. They are used in large, heavy vehicles, particularly those that need to carry and stop loads over long distances and downhill.

Air Compressor

Understand the function of the air compressor. It is driven by the engine through belts or a gear. The compressor fills the air storage tanks with compressed air.

Air Compressor Governor

The governor controls the air pressure levels in the air tank. Know how the governor works with the air compressor to maintain optimal air pressure.

Air Storage Tanks

Air storage tanks are used to store the compressed air. The number of tanks can vary depending on the vehicle.

2. Parts of the Air Brake System​

Service Brake System

Understand how applying the brake pedal uses air pressure to stop the vehicle.

Parking Brake System

Grasp the importance of the parking brake system. When the vehicle is parked, these brakes are manually applied for safety.

Emergency Brake System

Understand how the emergency brake system works. It is used when the service brakes fail. It uses parts of the service and parking brake systems to stop the vehicle.

Brake Pedal

Study the brake pedal and its connection to the brake system, including how it controls the air pressure release.

Foundation Brakes

Foundation brakes are used each time the wheels need to be slowed or stopped. Understand the different types of foundation brakes like ‘S-cam’ brakes, ‘wedge’ brakes, and ‘disc’ brakes.

3. Inspecting Air Brake Systems​

Pre-Trip Inspection

A pre-trip inspection of the air brake system is crucial. Study the necessary steps to inspect all components of the air brake system, including leaks, the air compressor, brake drums and shoes, and low air pressure warning devices.

Checking Air Pressure Build-Up

Comprehend the rate of air pressure build-up. It should typically build from 85 to 100 psi within 45 seconds in ideal conditions.

Checking Safety Valve

The safety valve protects the tank and the rest of the system from too much pressure. Understand how to test its function.

Inspecting Air Tank Drains

Understand the need for daily draining of the air tanks to get rid of moisture and compressor oil.

4. Using Air Brakes​

Proper Braking Techniques

Study the different braking techniques, such as controlled braking, stab braking, and their appropriate uses.

Brake Fading or Failure

Understand how and why brake fading or failure might occur, including the effects of overheating and strategies to prevent these occurrences.

Low Air Pressure

Understand what happens when the air pressure gets too low and how the spring brakes automatically come on.

Stopping Distance

Know the factors that impact the stopping distance of a vehicle, like perception distance, reaction distance, and braking distance.

5. Troubleshooting Air Brake Systems​

Know how to identify problems in air brake systems, what could potentially cause them, and how to address these problems. This includes understanding warning signs and signals like low air pressure warnings and system failures.

6. Safety Procedures​

Study safety procedures related to air brakes, including the proper use of air brakes in various weather conditions, downhill braking techniques, and procedures for parking and leaving the vehicle.

This study guide should provide a comprehensive overview of what you need to know about air brakes. However, it’s recommended to also use other resources like driver’s manuals, hands-on training, and practice tests to better prepare for the air brakes endorsement exam.

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