CDL - Section 5: AIR BRAKES

Air Brake System Overview

• Air tanks must be drained to remove water and compressor oil, preventing brake failure, especially in cold weather when water can freeze.
• Supply pressure gauges indicate the pressure level in air tanks.

Low Air-Pressure Warning

• A low air-pressure warning signal is mandatory for vehicles equipped with air brakes.

Spring Brakes

• Required on trucks, truck tractors, and buses for emergency and parking brakes; they rely on mechanical force since air pressure can leak.
• Powerful springs engage the brakes when air pressure is depleted, highlighting their critical safety role.

Braking Performance

• Front-wheel braking is effective under all conditions, including icy surfaces, reducing the likelihood of skids.
• Brakes on a long, steep downgrade serve as a supplement to engine braking, emphasizing the importance of engine assistance.

Brake System Components

• Vehicles with antilock brakes can be verified by checking the certification label for the manufacturing date.
• A dual brake system consists of two separate air systems controlled by a single set of brake controls.

Slack Adjusters

• Slack adjusters keep appropriate slack in the brake system; they must be checked by pulling on them to ensure movement is limited to about 1 inch.

Low Pressure Warning Signal Check

• To test the low pressure warning signal, shut off the vehicle while pressurizing the air system, then activate the electrical system and depress the brake. The warning should activate before pressure falls below 60 psi.

Automatic Engagement of Spring Brakes

• To verify that spring brakes engage automatically, fan brakes to lower air pressure until the tractor protection and parking brake valves close as per manufacturer standards.

Maximum Leakage Rates

• Allowable air loss rates are under 2 psi per minute for single vehicles and 3 psi for combination vehicles. After a brake pedal application, subsequent losses should be less than 3 psi for singles and 4 psi for combinations.

Parking Brake Protocol

• Always engage the parking brake when leaving the vehicle, regardless of the duration of absence.

Daily Maintenance

• Air tanks should be drained at the end of each driving day to ensure optimal performance of the brake system.

ABS Driving Techniques

• When operating a tractor-trailer combination with ABS, brake as normally required for safe stopping while maintaining control.

Functionality Without ABS

• Normal braking functions remain operational even when ABS is malfunctioning, ensuring safety.

Causes of Brake Fade or Failure

• Brake fade or failure can occur due to excessive heat from overuse or improper adjustment, emphasizing the need for regular maintenance and reliance on engine braking when necessary.