drum brakes

Overview of Drum Brake Systems

  • Advantages and disadvantages of drum brakes.

  • Current usage in vehicles such as cars and trucks.

  • Importance of knowing the drum brake system for shop work.

Introduction to Drum Brake Components

  • Differential Use:

    • Drum brakes are still in use today in various vehicles.

    • A personal example: Sold a 14-year-old car with 200,000 miles having original drum brake shoes that were still usable.

  • Key Components to Know:

    • Adjuster lever – critical for brakes adjustment

    • Return springs – help in retracting brake shoes

    • Wheel cylinder – hydraulic component for braking action

    • Parking brake components (cables, struts) – integral for parking functionality.

Functional Operation of Drum Brakes

  • Pressure Application:

    • The application of force on the brake pedal results in hydraulic pressure affecting the wheel cylinder.

  • Pressure Mechanics:

    • Notable difference between drum brakes and caliper brakes is in pressure application.

    • Drum brakes can push outward; as you push harder on the pedal, the fluid moves more into the wheel cylinder.

  • Drum Brake Functionality:

    • Drum brakes serve effectively as parking brakes due to larger surface areas and locking mechanism.

Brake Fade in Drum Brakes

  • Definition of Brake Fade:

    • Loss of stopping power due to excessive heat within the friction areas.

  • Types of Fade:

    • Mechanical Fade: Drum gets too hot and expands.

    • Gas Fade: Gasses forming between pad and drum reduce contact.

    • Lining Fade: Material degrading with increased temperature.

    • Water Fade: Water compromising brake efficiency.

  • Impacts of Brake Fade: Will result in a longer stopping distance and reduced brake response.

Self-Adjustment and Maintenance

  • Self-Adjusting Mechanism:

    • Drum brakes are designed to self-adjust, but might not function as intended.

  • Manual Adjustment Need:

    • Mechanical adjustments might be needed using the star wheel.

    • Importance of ensuring all components are operable during brake servicing.

Rear Drum Brake Components

  • Vacuum Plate:

    • Foundation of rear brakes; holds other components together.

  • Shoe Anchors and Contact Points:

    • Need lubrication; ensure they are not rusted or damaged to prevent poor function.

  • Brake Drums and Seals:

    • Labber seal creates a moisture barrier; crucial for maintaining performance.

  • Wheel Cylinder with Piston Stops:

    • Prevent overextension of the wheel cylinder pistons, safeguarding hydraulic integrity.

Brake Shoe Construction and Dynamics

  • Brake Shoe Parts:

    • Lining: Holds friction material; tapered edges prevent noise.

    • Web: Curved metal piece responsible for stable attachment.

  • Types of Brake Designs:

    • Dual Servo vs. NonServo:

      • Dual servo employs a primary and secondary shoe mechanism, enhances braking by utilizing the characteristics of rotation.

      • Non-servo utilizes trailing and leading shoes; roles can reverse based on the vehicle's direction.

Electrical System Integration

  • Overview of Wheel Cylinder:

    • Transfers hydraulic force to brake shoes; must have proper fluid connections for efficient operation.

  • Return Springs and Hold-Down Mechanisms:

    • Hold down springs secure shoe with backing plate; must ensure they are installed correctly for effective function.

Brake Maintenance Techniques

  • Cleaning and Lubrication:

    • Importance of regular service for all parts, especially rotary parts should be free of rust and obstructions.

    • Techniques for cleaning rust from drum brake surfaces to prevent grinding noises.

Drum Brake Operations During Usage

  • How Pressure Applies in Service:

    • Hydraulic action forces brake shoes against the drum to create friction.

  • Impacts of Worn Shoes:

    • Requires frequent adjustments to maintain proper pedal height and travel for effective braking.

Conclusion

  • Continued Education and Inspection:

    • Frequent brake checks and re-adjustments necessary for optimal vehicle performance and safety.

    • Importance of understanding the differences in brake systems to ensure accurate repairs and maintenance.