Car drum brake construction and parts

Auto Drum Brake Structure, Working Principle, and Components Overview

Drum brakes are one of the oldest braking systems used in many vehicles, especially older models or vehicles where compact packaging with high braking force is required. The drum brake system operates mechanically by applying brake shoes against the brake drum to slow down or stop the vehicle. The construction and working principle of drum brakes are relatively complex as they contain multiple components that work together to ensure effective and reliable braking.

General Working Principle of a Drum Brake:

The drum brake consists of brake pads, a wheel cylinder, and a brake drum, to which braking force is applied. When the brake pedal is pressed, the wheel cylinder uses hydraulic pressure to push the brake shoes against the drum, creating friction that slows down the vehicle.

The working principle of a drum brake is that the brake shoes move outward from the inside of the drum to stop the wheel’s rotation, while other parts of the braking system ensure smooth and efficient operation.


1. Anchor pin
2. Link spring
3. Brake Shoe
4. Parking brake cable housing retainer
5. Automatic adjuster spring
6. Parking brake cable and housing
7. Cable hook
8. Brake parking lever
9. Shoe holddown springs
10. Brake shoe
11. Parking brake lever retaining clip
12. Washer
13. Parking brake link
14. Shoe guide (anchor pin plate)
15. Working cylinder










Figure 1: Car Drum Brake Components


Drum Brake Components:

1. Anchor Pin

The anchor pin secures the brake shoe to the system frame, allowing the brake shoes to move towards the drum when braking is applied while keeping them securely in place within the system.

Function: The anchor pin ensures that the brake shoes remain firmly secured and do not move incorrectly within the system.

2. Link Spring

The link spring connects various brake components to ensure that the brake shoes move into the correct position. This spring helps maintain balance in the braking system, ensuring that the brake shoes move in sync when the brake is applied.

Function: The link spring helps keep the brake shoes in the correct position and ensures smooth operation of the system.

3. Brake Shoe

The brake shoe comes into contact with the inner surface of the drum, applying braking force to stop or slow down the vehicle. Brake shoes are made of materials that can withstand high temperatures and loads.

Function: The brake shoe creates friction against the brake drum to generate braking force.

4. Parking Brake Cable Housing Retainer

The parking brake cable housing retainer ensures that the cable remains in position to allow the reliable application of the parking brake.

Function: The retainer keeps the parking brake cable properly secured to ensure parking brake effectiveness.

5. Automatic Adjuster Spring

The automatic adjuster spring automatically adjusts the distance between the brake shoes and the brake drum to maintain optimal clearance, regardless of wear.

Function: The automatic adjuster ensures that the brake shoes move correctly and remain fully functional.

6. Parking Brake Cable and Housing

The parking brake cable and housing transfer the force from the parking brake lever to the braking system, ensuring the vehicle remains stationary.

Function: The cable and housing transfer the force from the parking brake lever to the braking system to apply the parking brake.

7. Cable Hook

The cable hook connects the parking brake cable to the mechanism, ensuring that the brake shoes move into the correct position.

Function: The cable hook connects the parking brake cable to the mechanism and allows precise movement.

8. Brake Parking Lever

The brake parking lever enables the movement of the brake shoes to keep the vehicle stationary.

Function: The brake parking lever manually applies the brake shoes to hold the vehicle stationary.

9. Shoe Holddown Springs

The shoe holddown springs keep the brake shoes securely in place within the brake assembly, preventing them from moving within the system.

Function: The holddown springs keep the brake shoes securely in place and ensure braking system precision.
10. Brake Shoe (Repeated Section)
Brake shoes are a key component of the braking system that make contact with the brake disc or drum's inner surface. They are made of durable materials capable of withstanding high temperatures and friction.

11. Parking Brake Lever Retaining Clip
The retaining clip is a part that secures the parking brake lever in place within the braking system mechanism. Its purpose is to ensure that the lever remains properly fixed and operates efficiently.

Function: The retaining clip holds the parking brake lever in the correct position to ensure effective operation.

12. Washer
A washer is a component commonly used in the braking system to secure different parts together. Its role is to ensure that components do not slip or shift, allowing the system to function smoothly.

Function: The washer keeps components in place to maintain system accuracy and reliability.

13. Parking Brake Link
The parking brake link is a component that connects the parking brake lever to other parts of the braking system, such as the mechanism that moves the brake shoes. This component transmits force to the braking system components, ensuring that the brakes engage properly.

Function: The link transmits force from the parking brake lever to the braking system and allows the brake shoes to move.

14. Shoe Guide / Anchor Pin Plate
The shoe guide plate directs the brake shoes into the correct position within the system. It ensures that the brake shoes move properly and without obstruction.

Function: The shoe guide plate helps keep the brake shoes in the correct position to maintain braking system precision and efficiency.

15. Working Cylinder

The working cylinder applies the brake shoes against the drum, generating braking force.

Function: The working cylinder moves the brake shoes against the drum and generates braking force.



1. Fixed shoe
2. Expander
3. Brake cable attachment (half shell)
4. Brake cable loop (cable eyelet)
5. Sliding shoe
6. Retention spring
7. Adjuster bolt
8. Shoe post
9. Adjustment wedge
10. Shoe post
11. Tension spring
12. Shoe steady spring
13. Tension spring











Figure 2: Car or Trailer Drum Brake Components


Conclusion:

The drum brake system is a complex and precisely tuned mechanism containing multiple components that work together to ensure effective braking. All parts, from the anchor pin to the working cylinder, must function harmoniously to make the braking system efficient and reliable. Regular maintenance and component replacement are necessary to keep the drum brake system dependable and long-lasting.