What is another name for a wheel hub?

Common alternative terms for a wheel hub include "hub" and, in automotive repair and parts sales, sometimes "wheel hub assembly." However, strictly speaking, a wheel hub and a wheel hub assembly are not exactly the same thing. Likewise, a wheel bearing should not be used as an exact synonym for a wheel hub.

What does the wheel hub connect to?

The wheel hub primarily connects the wheel to the vehicle's braking, suspension, and axle-related components. The wheel and, typically, the brake rotor or drum are mounted to the hub. The hub is supported by the wheel bearing, allowing it to rotate relative to the steering knuckle, axle, or other supporting components. On driven wheels, the hub also connects to the half shaft through splines to transfer driving torque to the wheel.

How does a wheel hub look?

A wheel hub is typically a round, disc-shaped metal component with a central section, located at the center of the wheel. It usually features a hub flange for mounting the wheel and brake rotor or drum, with wheel studs or wheel bolt holes arranged around the flange. The center may include a bearing mounting surface or bore and, on driven wheels, splines for connecting to the half shaft. Modern wheel hub assemblies are typically thicker and more complex because they may also incorporate the wheel bearing, an ABS wheel speed sensor, or a magnetic encoder.

Is a wheel hub the same as a wheel bearing?

No. The wheel hub and wheel bearing serve different functions. The wheel hub is a structural mounting component that connects the wheel to the vehicle, while the wheel bearing supports the hub and allows the wheel to rotate smoothly. Serviceable bearings may be removed, cleaned, repacked with grease, and adjusted, while bearings integrated into a wheel hub assembly are typically replaced as part of the entire assembly.

Is a wheel hub the same as a rim?

No. The rim is the outer part of the wheel that supports the tire, while the wheel hub is the central mounting component that connects the wheel to the vehicle. The wheel mounts to the hub, and the brake rotor or drum is also typically mounted to the hub. The rim and wheel hub are therefore different components.

Does a wheel hub assembly include a bearing?

Yes. A wheel hub assembly typically includes a wheel bearing as part of a preassembled unit. Depending on the design, the assembly may also include the hub flange, wheel studs or wheel bolt holes, an ABS wheel speed sensor or sensor provision, and a tone ring, reluctor ring, or magnetic encoder. The bearing is typically sealed to help protect it from water, dirt, and road debris.

What Are Drum Brakes? How They Work, Types, and Benefits

What Are Drum Brakes? Drum brakes are a common braking system used on cars, trucks, trailers, and other vehicles. This guide explains how they work, covers their key components and three main designs, and explores their advantages, disadvantages,

What Are Drum Brakes

Drum brakes rely on friction to slow and stop the vehicle. When the brakes are applied, the two curved brake shoes move outward and press against the inner surface of the brake drum, which rotates with the wheel. The friction between the brake shoes and the brake drum generates braking torque, converting the vehicle’s kinetic energy into heat and gradually reducing the wheel speed until the vehicle comes to a stop.
Some drum brakes use a leading-and-trailing shoe configuration, in which friction between the brake shoes and the brake drum creates a self-energizing effect that increases braking force. The brake drum is one of the key components of a drum brake. Its inner surface serves as the friction surface for the brake shoes, withstands the frictional loads generated during braking, and absorbs and dissipates the heat produced by friction.

NOTE

Braking torque is the torque that opposes wheel rotation during braking. It is primarily determined by the friction force between the brake shoes and the brake drum and the effective friction radius. In simplified form, it can be expressed as:M = F × R where M is the braking torque, F is the friction force, and R is the effective friction radius.

In a leading-and-trailing shoe configuration, as the brake drum rotates, friction between the drum and the brake shoes causes the shoes to press more firmly against the drum. This produces a self-energizing (servo) effect, allowing the brake to generate greater braking torque under the same input conditions.

Semi Truck Brake Drums: What Every Owner and Fleet Manager Needs to Know

Learn about semi truck brake drums, including semi brake drum weight, cost, warning signs, replacement steps, and DOT regulations. A complete guide for truck owners and fleet managers.

History of Drum Brakes

The development of drum brakes dates back to the early days of the automobile. In 1899–1900, Wilhelm Maybach began experimenting with drum-type braking designs. In 1902, Louis Renault was granted a patent for a drum brake and applied the design to automobiles.
From the 1960s onward, as disc brakes became increasingly common, drum brakes gradually became less common on passenger cars. However, their effective braking performance, durability, and relatively low manufacturing cost have allowed them to remain widely used on heavy-duty vehicles. Their relatively low drag losses have also led to renewed use on the rear axles of some new energy vehicles.

Drum Brake Components

A drum brake consists of several key components, including the brake shoes, friction linings, return springs, wheel cylinder, adjuster mechanism, anchor pin, backing plate, and brake drum. When the brakes are applied, the wheel cylinder pushes the brake shoes outward, forcing the friction linings against the inner surface of the brake drum to generate friction. When the brake pedal is released, the return springs retract the brake shoes to their original positions. The adjuster mechanism compensates for the increased clearance caused by friction lining wear, helping ensure that the brake maintains the proper operating clearance.

01.

Brake Drum

The brake drum is a cylindrical component that rotates with the wheel and is typically made of cast iron. Its inner surface serves as the friction surface for the brake shoes. When the brakes are applied, the friction linings press against the inner surface of the brake drum, generating friction that produces braking torque.
Over time, repeated braking gradually wears the inner surface of the brake drum, increasing its inside diameter. For this reason, manufacturers specify a maximum allowable inside diameter for the drum. If the drum exceeds this limit, it must be replaced.

02.

Brake Shoes & Linings

Brake shoes are curved metal components mounted inside the brake drum, with friction linings attached to their outer surfaces. When the brakes are applied, the brake shoes move outward, pressing the friction linings against the inner surface of the brake drum and creating friction that generates braking force. The friction linings are wear components that gradually become thinner with use and must be replaced once they reach the manufacturer’s specified wear limit.

03.

Wheel Cylinder

The wheel cylinder is the hydraulic actuator of a drum brake and is typically mounted near the top between the two brake shoes. When the brake pedal is pressed, pressurized brake fluid enters the wheel cylinder and pushes the internal pistons outward, forcing the brake shoes apart and pressing them against the brake drum.

04.

Return Springs

Return springs are attached to the brake shoes and pull them back to their original positions when the brake pedal is released. This allows the friction linings to maintain proper clearance from the brake drum, preventing continuous contact and unwanted drag.

05.

Anchor Pin

The anchor pin supports and positions the brake shoes, allowing them to pivot around the support point during braking while withstanding part of the braking force.

06.

Adjuster

The adjuster mechanism compensates for the increased clearance caused by friction lining wear, maintaining the proper operating clearance between the brake shoes and the brake drum. This helps maintain proper braking performance and pedal travel. Some drum brakes use an automatic adjuster that automatically maintains the proper operating clearance as the friction linings wear.

07.

Backing Plate

The backing plate is located behind the brake drum and serves as the mounting base for the drum brake components. It supports and secures the wheel cylinder, brake shoes, return springs, adjuster mechanism, and other components. It also withstands part of the reaction forces generated during braking, providing stable support for the entire brake assembly.

How Drum Brakes Work

When the brake pedal is pressed, hydraulic pressure is transmitted through the brake lines to the wheel cylinder, forcing the pistons outward and pressing the brake shoes against the brake drum. The resulting friction converts the vehicle’s kinetic energy into heat, causing the vehicle to slow down. When the brake pedal is released, the return springs retract the brake shoes, restoring the proper operating clearance.

Three Types of Drum Brake

Drum brakes are generally classified into three main designs based on the arrangement of the brake shoes and their self-energizing characteristics: leading-trailing, twin leading shoe, and duo-servo. The main differences between these designs lie in how the brake shoes are affected by friction forces during braking and how their braking performance varies when the vehicle moves forward or in reverse.

01.

Leading/Trailing Shoe

The leading-trailing drum brake is one of the most common drum brake designs and is widely used on the rear wheels of passenger cars. It typically uses a single wheel cylinder, with one brake shoe serving as the leading shoe and the other as the trailing shoe. As the direction of drum rotation changes between forward and reverse travel, the two brake shoes switch roles, allowing the brake to provide effective braking in both directions. Its main advantages are a simple design, low cost, and good reliability.

02.

Twin Leading Shoe

The twin leading shoe drum brake typically uses two wheel cylinders, each actuating one brake shoe. When the vehicle moves forward, both brake shoes act as leading shoes, providing greater braking force. When the vehicle moves in reverse, both shoes become trailing shoes, resulting in relatively lower braking force. This design is mainly used on the front wheels of light- and medium-duty trucks.

03.

Duo Servo Type

The duo-servo drum brake uses an adjuster link to connect the two brake shoes and transfer force between them. When the brakes are applied, friction between one brake shoe and the rotating drum produces a strong self-energizing effect. The resulting force is transmitted through the adjuster link to the other brake shoe, increasing the force with which it is pressed against the drum and thereby generating greater braking force and braking torque.
Because of its strong self-energizing effect, the braking torque of a duo-servo brake is relatively sensitive to the direction of rotation and friction conditions. This can also result in a somewhat nonlinear pedal response. Duo-servo brakes are commonly used as parking brakes on passenger cars, driveline brakes on trucks, and brakes on forklifts.

Advantages and Disadvantages of Drum Brakes

Discover the advantages and disadvantages of drum brakes to help you choose the right braking system for your vehicle.

Advantages of Drum Brakes

Low manufacturing cost.

Drum brakes have a simple design and are inexpensive to manufacture, making them a cost-effective choice for economy cars and commercial vehicles.

Self-boosting braking force

The servo effect increases braking force with less hydraulic pressure, allowing drum brakes to use smaller components while remaining cost-effective and efficient.

Protection from the elements

The enclosed drum protects brake components from water, mud, salt, and debris, improving durability in harsh conditions while also keeping brake dust off the wheels.

Easy parking brake integration

The design naturally supports a mechanical parking brake, using a cable-operated lever to press the shoes against the drum, providing a simple and reliable system that works independently of the hydraulic circuit.

Durability under moderate loads

Drum brakes have large friction surfaces and wear slowly, making them a durable choice for trucks, buses, and trailers, while their enclosed design helps ensure long service life and reliable operation.

Rusty Drum Brakes : Causes, Prevention, and How to Clean It

Rusty Drum Brakes is normal and usually harmless. Learn when to clean it, when to prevent it, and when to replace your drum brakes entirely.

How to Replace Drum Brakes: Step-by-Step DIY Guide

This guide for How to Replace Drum Brakes walks you through full drum brake replacement: pre‑job checks, required tools & parts, seven key steps from wheel removal to test drive, plus common mistakes to avoid.

Drum‑Brake‑Assembly‑Components_compressed

How to Check Drum Brakes

Learn how to check drum brakes step by step, including brake shoes, drums, wheel cylinders, springs, and self-adjusters. Identify wear, damage, and leaks before replacement is needed.

faq

A drum brake is a type of braking system that uses brake shoes and a rotating brake drum to slow or stop a vehicle. Its main components include the brake drum, brake shoes, friction linings, wheel cylinder, return springs, and adjuster mechanism.

A drum brake slows the vehicle by creating friction inside a rotating drum. When braking force is applied, the friction increases resistance to wheel rotation and converts the vehicle’s motion into heat. The amount of braking force depends on factors such as the brake design, friction characteristics, and applied hydraulic pressure.

Yes. Drum brakes are still widely used, particularly on the rear wheels of passenger cars, as well as on trucks, trailers, and other commercial vehicles. Their low cost, durability, and strong parking brake performance make them a practical choice for many applications.

Drum brakes typically last between 100,000 and 150,000 miles, although their service life varies depending on driving habits, vehicle load, road conditions, and maintenance. Regular inspection can help identify wear and determine when replacement is needed.

Drum brakes should be replaced when the brake shoes or drum have reached the manufacturer’s wear limits or show signs of damage. Common warning signs include unusual noises, reduced braking performance, vibration, or a damaged or excessively worn brake drum.

The cost of replacing drum brakes varies depending on the vehicle, parts required, and labor rates. Replacing the brake shoes alone is generally less expensive than replacing the shoes, drums, and other related components.

Neither is universally better. Drum brakes are generally more affordable and provide strong parking brake performance, while disc brakes offer better heat dissipation and more consistent braking under heavy use. The better choice depends on the vehicle and its intended application.

Yes. Drum brakes can overheat during repeated or heavy braking because the enclosed drum can retain heat. Excessive heat can reduce braking performance, increase brake fade, and accelerate wear of the brake components.

Drum brakes can make noise because of worn or contaminated brake components, improper adjustment, or vibration between the brake shoes and drum. Common noises include squealing, grinding, and clicking, which may indicate that the brakes need inspection or service.