Parking Brake System: Comprehensive Notes

Parking Brake Overview

• Definition and Purpose

  • The parking brake, traditionally known as the "emergency brake," is a system designed to keep the vehicle stationary when parked.

  • Originally necessary due to single master cylinder failures in older vehicles.

Historical Context

• Terminology

  • The term "parking brake" replaced "emergency brake" due to advancements in hydraulic systems.

Usage

• Common Practices

  • Many people do not regularly use their parking brake. A classroom inquiry showed that only manual transmission drivers typically engaged it daily.

  • The speaker insists on checking the parking brake only when it is applied on an older vehicle to prevent potential system damage.

Mechanical Considerations

• Brake Components

  • Manual Parking Brake

  • Pulling a handle or pedal should require:

    • Center handle: 80 foot-pounds of force.

    • Foot pedal: 100 pounds of force.

  • Automatic or Electronic Parking Brake

  • Operated through a vacuum system with various mechanisms for retraction and application.

Safety Practices

• Pulling Vehicles without a Functioning Vacuum

  • When towing a vehicle that won't start, the brake may seize due to lack of vacuum. Discussed a safety release mechanism in the vehicle design.

Parking Brake Functionality

• Holding Capacity

  • Parking brakes should support a fully laden vehicle (all fluids, properly inflated tires) on a 20% incline.

  • The instilled need for a parking brake to prevent rolling back or forward while in neutral.

Inspection and Maintenance

• Cable Conditions

  • Inspect for rust, corrosion, and swelling. A swollen cable indicates moisture ingress which leads to potential seizing.

• Brake Adjustment Procedures

  • When checking the parking brake, confirm the service brakes are operational as they affect the parking brake's efficacy.

Types of Braking Systems

• Dual Servo Drum Brake System

  • The parking brake lever connects only with the secondary shoe.

• Integral Parking Brake

  • Located within the brake rotor. This design improves engagement.

Mechanism Functionality

• Mechanical Operation

  • Describes the function of a parking brake within a caliper mechanism, integrating a hydraulic system with a twisting motion function.

  • Self-Adjustment: Critical for maintaining effective braking.

Adjustments and Tolerances

• Click Mechanism

  • Ideal manual application should take a minimum of 4 clicks to a maximum of 10 clicks for proper setting.

• Self-Adjustment in Calipers

  • Regular adjustments account for wear on the pads and drums. Self-adjustment is coupled with service brake operation.

Emerging Technologies

• Electronic Parking Brakes (EPB)

  • Operated by an electric motor that adjusts brake engagement automatically.

  • Specific service protocols must be followed when performing brake maintenance on vehicles with EPB systems.

Conclusion

• Consideration for Practice

  • Maintenance and inspection of parking brakes should integrate a thorough understanding of vehicle brake systems, including mechanical, hydraulic, and electronic operations.