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Drum Brakes

Last Update:

09/06/2016

Introduction

From the earliest block against wheel system, brakes underwent a revolution, especially with the development of the automobiles in the early 1900s. The brake system has come a long way since then. In the whole evolution, Drum Brakes were the earliest and most effective systems for braking invented which is still in widespread use today.

History:

  • Louis Renault is credited for inventing the drum brakes sometime during 1902. However, his was not the first drum brake.
  • Even before that, Wilhelm Maybach used a system similar to the drum brakes in Mercedes automobiles. The primitive drum brake was perhaps the one used by Gottlieb Daimler in 1899, making use of a cable wrapped around the drum and anchored to the chassis with a wood block serving as the brake. Although it was Renault’s drum brake that became widely adapted in the evolving automobiles.   
  • By 1903 the Dutch Spiker used four wheel drum brakes.
  • In 1909 the Scottish Company, Arrol Johnston used four wheel brakes in its car.
  • The tipo KM4 from Isotta Franschini sported four wheel drum brakes from 1911 to 1914.
  • The initial Mechanical Drum Brakes gave way to more evolved and efficient Hydraulic Drum Brakes by 1920s.
  • The Duesenberg, Maxwell Chalmers and Chrysler Phaeton used hydraulic drum brakes between 1921 and 1924, which were widely adopted in most cars by 1967.

 

Evolution and Improvements

  • One of the earliest Drum Brake was developed by Ransom E. Olds.

- A stainless steel flexible band was fitted around a drum on the rear axle.

- The band was actuated by depressing the brake pedal and resulted in its gripping the drum.

However, the modern drum brake employs a cast iron drum inside which two curved shoes that matches the curvature of the drum are fitted with one end attached to a pivot and the other to the actuating rods.

  • When the brake pedal is pushed the shoes expand and grip the inner surface of the drum resulting in halting of the vehicle.
  • A third type involved a drum with the shoes on the outer surface. The shoes pinched the drum and were known as pinch drum brakes.
  • Drum brake designs can be further categorized in leading/ trailing and twin leading systems.

The leading/trailing system employs a design in which one of the shoes is of the self applying types, usually fitted in the rear wheels.

  • Twin leading systems are employed on the front wheels where two actuating cylinders work on both shoes in the drum with brake shoes pivoting in opposite directions to deliver maximum braking effect when the vehicle is moving forwards.

 

Main Parts

  • The main components of the basic drum brake are the main drum, usually made of cast iron, two curved brake shoes with asbestos lining, springs and backing plate.
  • A hydraulic brake has additional components comprising of a wheel cylinder on each wheel with a piston to actuate the brake shoes, hydraulic hoses and master cylinder.

There are minor parts such as linkage, self-adjusting components and hold down hardware making up the assembly.

How It Works

In the simplest mechanical drum brake, the brake pedal transmits force to the shoes that expand and clamp against the drum resulting in stopping motion. Hydraulic drum brakes are operated a bit differently.

  • When the brake pedal is pushed it exerts pressure in the master cylinder and the pressure is transmitted through hoses to the wheel cylinder.
  • Movement and distance are translated to force.
  • Hydraulic pressure in the wheel cylinder causes a piston to clamp the brake shoes against the drum’s inner surface.
  • When pressure is released the springs help the shoes return to their original position.

Drum brakes were refined with the addition of power assisted braking that used vacuum in the manifold. In the electrohydraulic system an electric motor operates the hydraulic pump and creates braking pressure. The systems were further refined with development of ABS systems.

Effectiveness and Challenges

Drum brakes, when maintained properly, works most effectively. With the right design, drum brakes can bring a vehicle to a halt quickly, especially when hydraulics are employed.

  • Drum brakes have fewer parts and require less maintenance while being highly reliable.
  • The friction is at the circumference of the drum, which results in higher braking force.
  • Brake shoes have a larger surface area and will last longer.
  • Heat is generated but it is also easily dissipated.
  • Drum brakes are less expensive as it lasts longer compared to others.
  • Drum brakes are used on rear wheels and also for emergency hand brake with simple and easy to maintain layout.

The disadvantages are that it requires a larger drum surface and larger shoe area to generate enough braking power.

  • Also, the heat generated in the system is too high that can cause the wear inside the drum over time.
  • Much higher braking effort is required on the part of the driver.
  • Brake shoes can wear down with too much heat and quick cooling which can eventually reduce braking force.
  • Drums wear out increasing gap between shoe and drum surface with consequent reduced braking power.
  • Drum heating can vaporize wheel cylinder brake fluid, reducing pressure and may require regular maintenance.
  • Drum brakes face challenges from more recent and widespread use of disc brakes as well as brake by wire technologies. Still, it is a tried and tested system with economical braking technology that could do with improvements in the size and choice of braking shoes and linings, drum material and more reliable hydraulic systems.

 

Maintenance Tips

  • Maintain hydraulic system by checking for leaks, hose cracks and ruptures as also the rubber seals in the master and wheel cylinders.
  • Change brake shoes regularly.
  • Replace brake fluid as recommended, especially after rains since brake fluid absorbs moisture.
  • Check for air in the hydraulic lines and purge.

Drum brakes have been in use since well over a century and will endure despite the rise of other systems because of their inherent simplicity and ease of maintenance.

 

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