Drum Brake: Diagram, Parts, Working, Types and Applications

Hi there, readers! We'll talk about what a drum brake is in this article. Using drawings, describe its components, benefits, functions, and applications.

When slowing down or stopping a moving vehicle, a mechanical braking device called a drum brake is often utilized. The brake shoes' friction on the inside surface of a drum-shaped part that is fastened to the wheel is what drives this braking system.

Although disc braking systems with more sophistication have made drum brakes less widespread in recent cars, drum brakes nonetheless have a long history and are used in many different automotive applications.

What is Drum Brake?

Using the friction created when a set of shoes or pads applies pressure outward against a revolving, cylinder-shaped braking drum, a drum brake works. Generally speaking, a "drum brake" is a braking system where the shoes press on the drum's inner surface.

It's called a clasp brake when shoes make contact with the exterior of the drum. These brakes are quite uncommon, but because the drum is squeezed between two shoes, just like a regular disc brake, they are sometimes called pinch drum brakes.

There are two types of drum brakes: twin leading and leading/trailing. Rear drum brakes are usually made with leading/trailing or primary/secondary shoes that hinge in the same location and are manipulated by a single double-acting hydraulic cylinder. The self-applying effect always affects one brake shoe, whether the car is moving forward or backward.

 The parking brake, also known as the handbrake, must deliver enough power to keep the cars in place and prevent it from rolling backward, therefore this is especially helpful when using the rear brakes. As long as the brake shoes' contact area is sufficiently large, the self-applying effect can safely retain a vehicle during inclining or reversing motion.

Let's talk about the drum brake's essential components.

Parts of Drum Brake

The essential components of a drum brake are as follows:

1. Drum brake
2. Braking plate
3. Brake shoe with pads
4. Wheel cylinders
5. Brake lever
6. Brake shoe holder
7. Return spring
8. Parking brake cable
9. Brake shoe adjuster

#1 Drum Brake

It's a crucial component in the drum brake work system. This part is shaped like a tube or drum and has a rough feel since it is made of cast steel.

This part's main purpose is to act as a medium for friction between the brake pads and the wheel so that the vehicle can stop. The drum may revolve in unison with the wheel bolts since this part is also directly attached to them.

#2 Braking Plate

One component of the drum braking system is the backing plate. It resembles a thin metal band that is fastened to the rear of the system. The remaining parts of the drum brake are shielded by this component.

The backing plate has several holes and protrusions in a circular pattern. The main reason the backing plate has a specific number of holes is to match the drum brake's standard component.

#3 Brake shoe with pads

Brake shoes and brake pads are additional parts that are commonly found in drum brakes. Brake shoes or brake pads are used to apply the brakes in a drum braking system. The disc brake components' brake pad is where the brake pads are supposed to be installed.

The shape of a typical brake shoe is a circle formed by two shoes joined by a semicircle. The brake shoe will not make direct contact with the drum even if it is mounted in one section of the drum brake.

#4 Wheel Cylinders

Wheel cylinders and other drum brake components are helpful in converting fluid pressure into mechanical motion. There are several different types of wheel cylinders that are often used in drum braking systems.

The twin piston wheel cylinder type is the most often used because it is often used in conjunction with leading and trailing drum types. The best way to identify the double piston type from the backing plate is through bolts.

The wheel cylinder housing, bleeder nut, piston boot, spring, and piston are the parts that make up the wheel cylinder. The efficacy of the drum brakes will be diminished in the event that one of the wheel cylinders malfunctions.

#5 Brake lever

Motorbikes do not employ drum brake components, thus items like the parking brake lever are exclusive to vehicles. When the parking brake lever is attached, the drum brake system will seem more intricate. The two levers that make up the parking brake lever system are the park brake lever and the brake shoe link.

The parking brake lever is made comprised of an arm with the brake cable attached at one end and a hinge at the other that is hooked to the top side of the brake shoe. The park brake lever and the opposing brake shoe are connected by the brake shoe link.

#6 Brake Shoe Holder

In an automobile drum braking system, the brake shoes will normally be installed or stored connected to the backing plate. The brake shoe holder is dynamic or moves with ease. The holding mechanism may support the drum brakes correctly in this way.

The brake shoe holder is made up of a pressure plate and many pins with spring-loaded or spring-locked pins. The three pieces come together to create a crucial portion that attaches to the backing plate.

#7 Return Spring

The fact that return springs restore the brake shoe to its initial position prior to the application of brake lever or pedal pressure makes them brake parts no less significant. Two return springs are used in this braking system: the upper and lower springs.

Above or below the cylinder wheel are the springs known as upper springs. Main function of the upper spring: to return the brake shoe to its initial position.

There is a big difference in the function of the upper and lower springs, which are located on the adjuster's side. For the purpose of applying pressure to the adjuster, the lower spring holds the two brake shoes in position.

#8 Parking Brake Cable

Usually, the brake system is pulled using the parking brake wire. Steel is used to make it. As with other steel cables, this specific type of cable is not really special.

The primary function of the parking brake cable is to connect the parking brake lever of the braking system to the parking brake lever action.

#9 Brake Shoe Adjuster

The brake shoe adjuster, which resembles the adjuster's screw, is one of the parts of the drum brake. The shoe adjuster on these brakes is a crucial component.

When the brake pedal is depressed, the brake shoe adjuster modifies the space between the drum brake pads and the drum surface.

Working Principle of a Drum Brake

The brake booster, sometimes referred to as the servo system, intensifies the force applied by the driver when they depress the brake pedal. The master cylinder then transforms this force into hydraulic pressure, or oil pressure. The braking mechanisms at each wheel receive this hydraulic pressure through brake fluid-filled tube. The pistons on the brake assemblies of all four wheels are engaged by the pressure when it reaches these brakes.

 The adjustment constantly keeps the brake shoes in close proximity to the drum since they can advance as soon as they start to wear a bit more. The adjusters often work best while the car is in reverse and the brakes are applied.

To close large gaps, it could be required to manually adjust the brakes on cars without automated adjusters. The brakes are controlled by a system of steel wires that are linked to a hand lever or a foot pedal via the parking (or emergency) brake system.

Even in the event that the hydraulic brakes totally fail, the vehicle can still be stopped by the mechanical braking system. Here, a cable that is directly attached to the brake shoes pulls a lever that is positioned on the brake.

Types of Drum Brakes

The different types of Drum Brake Systems are enumerated below:

Mechanical Drum Brake

Applications for the mechanical drum braking system include auto rickshaws and two-wheelers. In this arrangement, the brake shoes are operated by a cam that is attached to the brake linkage and pedal. When the brake pedal is depressed, the cam rotates, causing the brake shoes to spread apart and come into contact with the drum. 

The friction created by this contact between the brake linings and the drum causes the drum to stop rotating, which in turn stops the wheel from moving. Retracting springs allow the brake shoes to return to their initial position when the brake pedal is released, enabling free rotation to resume by forming a space between them and the drum.

Hydraulic Drum Brake

Commonly used in autos, the hydraulic drum brake is a step forward of the mechanical system. A hydraulic wheel cylinder takes the role of the cam in this configuration. The wheel cylinder's pistons use force in this hydraulic arrangement to press the brake shoes outward.

The anchor plate, also known as the braking plate, is where the brake shoes are mounted. It unifies the many parts of the brake system and fastens them to the axle of the car. When the brake pedal is depressed, the brake master cylinder's hydraulic force multiplier increases, increasing the pressure that is sent to the wheel cylinders.

The brake shoes are then forced outward by the pistons as a result, creating friction between the drum and the linings. The friction that results stops the drum from rotating, which stops the wheel from moving.

Pneumatic-Assisted Drum Brake:

The third kind, known as the pneumatic-assisted drum brake system, operates on the same principles as the mechanical drum brake system and is powered by air pressure. It is based on what is known as the "S-Cam" braking system, which is a bigger or 'S-shaped cam. But what makes this unique is that a pneumatic piston is activated by high-pressure compressed air, which then moves the cam. 

This arrangement is mostly utilized in medium-to-large commercial vehicles, where the braking process is started by the action of the pneumatic piston on the cam. The brake shoes' outward expansion creates friction between the brake linings and the drum, which stops the drum from rotating and immobilizes the wheels.

Leading or Trailing Shoe Type Drum Brake:

The "leading shoe" (or "primary shoe") is the revolving shoe that makes contact with the drum. The opposite shoe is referred to as the "trailing (secondary) shoe". The shoes are pressed in the same direction as the drums revolve. This rotation applies additional pressure to the shoes' contact with the drum, resulting in a stronger braking action.

This produces the servo effect (self-boosting effect), which gives drum brakes their incredible braking strength. The wheel cylinder, which includes a piston, generates hydraulic pressure, pushing the two shoes against the drum's internal surface.

When the vehicle moves forward or backward, the two shoes alternate between being the trailing shoe and the leading shoe. Whether the car is going forward or backward, the brakes always provide braking force.

This is due to the fact that drum brakes apply the same amount of braking force in both directions. This kind of system is often utilized for the back brakes of a passenger car.

Twin Leading Shoe Type Drum Brake: 

The drum brake features two wheel cylinders and two leading shoes. When the car is going forward, each wheel cylinder pushes on one shoe, thus both shoes function as the leading ones, increasing the stopping power of the brakes.

When the car is in reverse, both shoes function as the trailing ones since each piston in the wheel cylinders can only travel in one direction. This particular type is commonly used for front brakes in small to medium-sized trucks.

Regardless of the direction the vehicle is traveling in, both shoes can function as the leading ones when dual twin leading shoes are used. The majority of them are found on small to medium-sized vehicles equipped with rear brakes.

Duo Servo Type Brake: 

The duo servo mechanism has an adjustment that links two brake shoes, known as the primary and secondary shoes. The primary shoe's servo effect (self-boosting effect), which applies extreme pressure to the coupled secondary shoe, creates a significant amount of braking force. This type of brake has three major applications: parking brakes, truck center brakes, and forklift brakes.

Materials Used in Drum Brakes 

Brake drums can be made of aluminum, cast iron, or steel. An explanation of this is provided below:

Aluminum:

Aluminum brake drums are greatly lighter than cast iron, which can help to reduce overall vehicle weight. Aluminum's excellent thermal conductivity improves heat dissipation, lowering the possibility of brake fade and ensuring constant braking performance.

Cast Iron:

Cast iron is well-known for its toughness and ability to tolerate high temperatures and friction caused by braking. Because of their durability, cast iron brake drums are widely employed in a variety of vehicles, including passenger automobiles and heavy-duty trucks.

Steel:

Steel brake drums are commonly utilized in heavy-duty and commercial vehicles due to their strength and ability to withstand large weights. Steel is a good material for automobiles that are frequently subjected to harsh braking and hard running conditions because of its durability and wear resistance.

Advantages of Drum Brake

Following are the advantages of the drum brakes:

1. Drum brakes feature a simple design and components.
2. It is manufactured at a low cost.
3. These brakes have a longer lifespan.
4. The performance of drum brakes is reliable.
5. It is possible to add drum brakes to earlier car models.
6. Drum brakes are less likely to become contaminated by brake fluid leaks than disc brakes because of the way they are internally constructed.

Disadvantages of Drum Brakes

Following are the disadvantages of the drum brake:

1. Drum brakes take longer to stop than disc brakes.
2. After a period of usage, they may lose some of their effectiveness.
3. This type of brake warms up quicker.
   
4. Certain drum brakes have asbestos fibers in the brake lining that can be dangerous.
   
5. Drum brakes may not perform effectively in rainy weather.
   

Drum Brake vs. Disc Brake

The following section discusses the differences between disc and drum brakes:

Conclusion

Brake linings are pressed up against the inner surfaces of the drums to create friction. Kinetic energy is transformed into thermal energy by this friction. When compared to disc brakes, the better braking force provided by drum rotation is due to the increased force with which the shoes and lining are pressed against the drum. However, it is crucial to build the parts in a way that allows thermal energy to be effectively released into the environment.

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FAQs

#1 Why are drum brakes more durable than other brakes?

Drum brakes often have a longer lifespan because of their enclosed construction, which protects against the weather and exposes them to less wear-inducing variables.

#2 Are drum brakes superior to disc brakes?

Because each type of brake has pros and cons of its own, whether drum brakes are superior to disc brakes depends on a number of factors, including cost, application, and preference.

#3 Why did we no longer use drum brakes?

Compared to disk brakes, drum brakes are less effective and more difficult to maintain. Moreover, drum brakes will fade and overheat faster than disk brakes, resulting in a longer stopping distance.

#4 Do drum brakes provide safety?

In conclusion. Drum brakes are vital to the safety of both you and your car if your car is equipped with them. When doing regular maintenance and repairs, be sure to check the drum brake for wear and efficacy.