Even though the Maybach car introduced the modern automobile drum brake in 1900, Louis Renault didn’t patent the idea until 1902. Although Maybach had used a less complex drum brake, he nevertheless used woven asbestos lining because the asbestos lining was the only material that successfully dispersed heat. In the early drum brakes, the shoes were mechanically actuated by levers, rods, or cables. Although some vehicles continued to use purely mechanical brake systems for decades, oil pressure in tiny wheel cylinders and pistons began to actuate the brakes as of the mid-1930s. Two-wheel cylinders are featured in some designs.
Up until the introduction of self-adjusting drum brakes in the 1950s, brakes required routine manual adjustment as the shoes in drum brakes wore out. With repeated usage, drum brakes are likewise susceptible to brake fade. Well, in this article, we’ll get to discuss the definition, working, types, components, bad symptoms, advantages & disadvantages of a drum brake. We’ll also be looking at a drum brake diagram.
Read more: Understanding brake shoe
Ok then, let’s get to it.
What is a drum brake?
A brake drum is a rotating cylinder-shaped component that presses outwardly on a set of shoes or pads to create friction. Drum brakes are brakes where the inner surface of the drum is pressed by the shoes. It is commonly referred to as a clasp brake when shoes press against the drum’s exterior. Though such brakes are extremely uncommon, they are frequently referred to as pinch drum brakes when the drum is pinched between two shoes, much like a traditional disc brake. A band brake, a related design, wraps a flexible belt or “band” around the outside of a drum.
Leading/trailing (also referred to as “single leading”) or twin leading are the two common classifications for drum brakes. Typically, rear drum brakes have leading/trailing or primary/secondary designs, with the shoes being moved by a single double-acting hydraulic cylinder and hinged at the same location. No matter whether the vehicle is traveling forward or backward, one of the brake shoes always experiences the self-applying effect with this design.
This is especially beneficial when using the rear brakes, where the parking brake (handbrake or footbrake) needs to apply enough pressure to hold the car in place while preventing it from rolling backward. The self-applying effect can safely retain a vehicle when the weight is moved to the rear brakes due to the incline of a hill or the reverse direction of motion, provided the contact area of the brake shoes is large enough, which isn’t always the case. Using a single hydraulic cylinder at the back also has the benefit of allowing the opposing pivot to be turned into a double-lobed cam that rotates in response to the parking brake system.
Read more: Understanding brake fluid
Drum brake diagram
Drum brake working principle
The working principle of a drum brake is pretty straightforward:
As the driver presses the brake pedal, the brake booster (vacuum servo) intensifies the force and the master cylinder converts it into hydraulic pressure (oil pressure). Using a brake oil-filled tube, the pressure is transferred to the brakes on the wheels (brake fluid). The pistons on the four-wheel brakes are pushed by the pressure that is applied. The brake linings, which are friction materials, are pressed by the pistons onto the interior surfaces of the brake drums, which revolve around the wheels. The linings are forced onto the rotating drums, which causes the wheels to slow down and eventually come to a stop.
The distance the shoes must travel to reach the drum increases as the brake linings deteriorate. With systems with automatic adjusters, a self-adjusting mechanism automatically adjusts by moving the shoes’ rest position closer to the drum when the distance reaches a particular point. The adjustment lever here moves only enough to move the adjuster gear forward by one tooth. The adjuster is threaded like a bolt so that when it revolves, it slightly unscrews and lengthens to close the gap. The adjustment always keeps the brake shoes near the drum because they can advance again when the brake shoes start to wear a little more. The adjusters often only work when the brakes are on and the car is in reverse.
It is necessary to occasionally manually adjust the brakes on vehicles without automatic adjusters to close any excessive gaps between the shoes and drum. Via a system of steel cables that are attached to either a foot pedal or a hand lever, the parking (or emergency) brake system controls the brakes. To stop the car even in the event of a complete brake failure, the system is designed to be entirely mechanical and to completely avoid the hydraulic system. Here, the cable is attached directly to the brake shoes and pulls on a brake-mounted lever. Bypassing the wheel cylinder as a result, the brakes are directly controlled.
Read more: Things you need to know about brake pads
Types of drum brake
Here are the types of drum brakes:
- Leading/trailing shoe-type drum brake
- Duo servo type drum brake
- Twin leading shoe type drum brake
Leading/trailing shoe-type drum brake
Leading (or primary) shoe is a word used to describe the shoe that rotates when it is placed up against the drum. The “trailing (secondary) shoe” is the other shoe. The leading shoe is pressed in the same direction as the drums’ rotation, and this rotation aids in applying more pressure to the shoes’ contact with the drum for a more potent braking effect. This produces the potent braking forces of drum brakes, known as the servo effect (self-boosting effect). The two shoes are pushed on the inner surface of the drum by hydraulic pressure produced by a wheel cylinder that houses a piston.
The two shoes operate so that, depending on whether the vehicle is moving forward or backward, each one becomes either the trailing shoe or the leading shoe. No matter whether the vehicle is moving forward or backward, drum brakes produce uniform braking force. Drum brakes produce the same amount of braking force in both directions, which explains this. This kind is typically utilized for the passenger car’s rear brakes.
Twin leading shoe type drum brake
This style of drum brake features two leading shoes and two-wheel cylinders. When the car is moving forward, both shoes operate as the leading ones since each wheel cylinder exerts on one of them, giving the brakes a stronger stopping power. When the car is in reverse, both shoes function as the trailing ones since each of the pistons housed in the wheel cylinders moves in just one direction. For small-to-midsize trucks’ front brakes, this type is typically utilized.
The dual twin leading shoe type includes pistons that can move in both directions, allowing both shoes to function as the leading ones no matter which way the vehicle is moving. Small-to-midsize trucks with rear brakes use mostly this type.
Duo servo type drum brake
Two brake shoes, referred to as the primary shoe and secondary shoe, are connected by an adjuster in the duo servo type’s mechanism. Strong pressure from the primary shoe’s servo effect (self-boosting effect) is transferred to the linked secondary shoe, creating a significant amount of braking force. Forklift brakes, truck center brakes, and parking brakes are the three principal applications for this kind of brake.
Drum brake system component
Here are the major components of a drum brake:
- Drum Brake
- Backing Plate
- Brake Shoes with pads
- Wheel Cylinders
- Parking Brake Lever
- Brake Shoe Holder
- Return Spring
- Brake Shoe Adjuster
- Parking Brake Cable
The drum brake is a part that is crucial to the drum brake operation system. This part has a strong texture and a drum- or tube-like shape since it is composed of cast steel. The major objective of the drum brake is to provide a surface for friction between the brake pads and the wheels so that they can stop on the road. Also, the drum will rotate in tandem with the wheel bolts thanks to this component’s direct connection to them.
The backing plate is one of the drum brake system’s components. It takes the shape of a thin metal band that is attached to the system’s rear. Other drum brake components are protected by this component. The backing plate is shaped like a circle with several holes and protrusions. The backing plate’s major function in having a certain number of holes is to match the standard component of the drum brake.
Brake Shoes with pads
Another component that is frequently seen in a drum brake is brake shoes and brake pads. When a drum brake system is in use, the brake is applied using a brake shoe or brake pad. Brake shoes typically have a form that looks like a circle made up of two shoes connected by a semicircle. The brake shoe won’t touch or come into direct contact with the drum despite this component being installed in one area of the drum brake. Components like brake pads are directly attached to the brake shoe’s surface. When the brake pads are worn or in bad condition, they can be changed or replaced because the substance used to make them is an organic ceramic.
Drum brake components, such as wheel cylinders, are useful for transforming fluid pressure into mechanical motion. Drum braking systems often use or contain a variety of wheel cylinder types. The leading and trailing drum kinds frequently accompany the dual piston wheel cylinder type, making it the most prevalent wheel cylinder type. The double piston type of the backing plate is best described by its bolts. The wheel cylinder housing, bleeder nut, piston boot, spring, and piston are the several components that make up the wheel cylinder. The performance of the drum brakes as a whole will be impacted if one of the wheel cylinders is not functioning properly.
Parking Brake Lever
One of the drum brake parts that are exclusive to cars because they cannot be utilized on motorcycles is the parking brake lever. The drum brake assembly will appear more complicated with the parking brake lever. The park brake lever and the brake shoe link are the two levers that make up the parking brake lever system. The parking brake lever is constructed with an arm that has a hinge at one end that is attached to the brake shoe on the top side and the brake cable at the other end. The park brake lever will be connected to the other brake shoe by the brake shoe link in the meantime. The out says that the brake shoes will be mounted or stored attached to the backing plate in an automobile drum braking system. The brake shoe holding moves easily or is dynamic. In this manner, the drum brakes can be properly supported by the holder mechanism. The brake shoe several up of several pins with spring locks or spring-loaded pins as well as a pressure plate. When the three parts are combined, they form a crucial component that attaches to the backing plate.
Due to its role in returning the brake shoe to its initial position before the use of the brake lever or pedal pressure, the return spring is a drum brake component that is no less significant. The top spring and lower spring make up the two return springs in the drum brake work system. A spring or springs that are positioned above or beneath the cylinder wheel are referred to as upper springs. The upper spring’s main job is to put the brake shoe back in its rightful place. The lower spring, which is situated on the adjuster’s side, serves a very different purpose from the top spring. The bottom spring keeps the two drum brake shoes in place so they can apply pressure on the adjuster.
Brake Shoe Adjuster
One of the drum brake parts at the bottom of the drum brake is the brake shoe adjuster, which has a shape similar to the adjuster’s screw. A somewhat significant part of drum brakes is the brake shoe adjuster. When the brake pedal moves, however slight, the brake shoe adjuster adjusts the distance between the drum brake pads and the drum surface.
Parking Brake Cable
The parking brake cable is part of a drum brake system that is often used to pull the drum brake system. It is made of steel. The utilized cable is similar to other steel cables kinds in many ways. The parking brake cable’s main job is to link the drum brake system’s parking brake lever to the parking brake lever action.
Symptoms of a bad drum brake
Here are the most common signs and symptoms of a bad drum brake system:
You expect your car to come to a quick stop when you press the brake. This stopping time will steadily lengthen as the brake drums begin to deteriorate. If the car isn’t stopping as well as it once did, there might be a problem with the brake shoes or drums. On the other hand, your car can have brake drums on the back wheels and braking discs on the front. As both sets exhibit stopping problems when they are worn, it can be challenging to determine which set is malfunctioning in this situation.
The brake pedal vibrates
You will start to experience pedal performance issues when the brake drums deteriorate. There may be some vibrations when you depress the brake pedal to stop the car. At first, especially if no other symptoms have manifested, you might not give it much thought. This early warning sign, though, is trying to catch your attention. Before the other issues arise, you may save a lot of headaches and ensure optimal stopping power by replacing the brake drums immediately.
When you press the brake pedal, there shouldn’t be any strange noises if the brakes are working properly. Yet, as they age, the brakes get louder. The heat produced during braking is no longer able to be absorbed by worn-out brake drums. As the temperature rises, the brakes are put under more strain, which results in noises made when the shoes contact the drums.
Unstable Parking Brake
In most cars, the back wheels are used as the parking brake. Moreover, the majority of brake drums are found here. When applied, the parking brake relies on sturdy brake drums to keep the car in place. The drums may not have the necessary holding strength to keep the car in place if they are worn. When you initially try to engage the parking brake, you can experience a loose sensation. After application, it may sometimes feel like it is slipping a little.
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Advantages and disadvantages of a bad drum brake
Advantages include the following:
- Compared to a disc brake with an equivalent diameter, drum brakes may offer higher braking power.
- Drum brakes have a larger friction contact surface than a disc, thus they last longer.
- Manufacturing drum brakes are less expensive than disc brakes.
- Drum brakes contain an internal self-energizing mechanism that reduces the need for external force (such as hydraulic pressure).
- It is easier to repair wheel cylinders than disc brake calipers.
- Drum brakes towards the back produce less heat.
- For later use, brake shoes can be reconditioned.
- Drums have slightly less frequent maintenance needs because they withstand corrosion better.
Disadvantages include the following
- The diameter of the drum somewhat expands with strong braking due to thermal expansion, requiring the driver to press the brake pedal farther.
- Heavy braking may result in excessive heating, which may subsequently cause the drum to deform and vibrate as a result.
- The reverse of fade is grab, which occurs when the applied force increases as a result of the brakes’ inherent tendency to aid the driver. If the brake pad friction is sufficient, the brake will continue to apply itself even after the externally applied force is released.
- Brake shoes are susceptible to overheating to the point where they glaze over.
- The brake fluid may evaporate as a result of excessive brake drum heating.
Drum brake replacement cost
Depending on the type of vehicle you drive and the sort of shop you choose, the typical cost to replace a brake drum ranges from $275 to $399.
Read more: Brake pad and rotor replacement cost
What does a drum brake do?
No matter whether the vehicle is moving forward or backward, drum brakes produce consistent braking force. This is due to the fact that drum brakes produce the same braking force in both directions. This kind is typically utilized for the passenger car’s rear brakes.
Are drum brakes better than discs?
Disc brakes of the same diameter cannot match the braking power of drum brakes. Drum brakes have a larger friction contact surface than a disc, thus they last longer. Manufacturing drum brakes are less expensive than disc brakes. Drum brakes towards the back produce less heat.
Why did we stop using drum brakes?
Safety. Discs may be considered to be safer than drums because of their better heat capacity. Yet, your front brakes have the majority of the braking force. Your rear brakes experience less strain and heat even during panic stops than your front brakes do.
Do cars still use drum brakes?
Nevertheless, modern cars still frequently use drum brakes. As the front wheels must work the hardest, manufacturers typically install disc brakes there and drum brakes in the back. Certain sports cars have disc brakes on all four wheels, but some also have a parking drum brake.
What are the disadvantages of drum brakes?
Disadvantages of drum brakes
- They need time to break into their components. Brake shoes need more time to break in than disc brake pads.
- Poor heat dissipation. When drum brakes are unable to distribute the heat produced by friction, a ventilation issue arises.
How long can drum brakes last?
While the shoes are anticipated to last for 30,000 to 40,000 miles, drum brakes are intended to be operational for around 150,000 to 200,000 miles. However, these ratings are based on typical driving conditions, and a number of things could shorten the lifespan of the brake drums.
Why does Toyota use drum brakes?
Drum brakes are more suitable for use as a parking/emergency brake, therefore that’s a good reason to use them back there. Drums are more affordable and are of sufficient quality. If you use rear disks, you must create a parking brake drum brake inside the disc rotor.
Are drum brakes safer?
The vast friction area of the drum brake makes it a more effective and safer alternative. Both the manufacturers and the user will save money by using it. They offer security and efficiency, making them a safer option for automakers.
Why is it called a drum brake?
Because the parts were stored in a circular drum that rotated with the wheel, they were known as drum brakes. There was a set of shoes inside that would press against the drum when the brake pedal was depressed, slowing the wheel.
Brakes should typically be inspected at least once every 10,000 miles. Nonetheless, the lifespan of rear drum brakes is often twice that of front disc brakes. You can get away with checking the rear brakes every other time you check the front brakes if you know when they were last inspected. So that concludes this article, where they got to discuss close to everything you need to know about drum brakes. Nevertheless, we were able to discuss the definition, working, types, components, bad symptoms, advantages & disadvantages of a drum brake. We also looked at the drum brake diagram. I hope you learn a lot from the reading. If you do, kindly share it with others. Thanks for reading; see you around!