Drums vs. Air Disc Brakes – Learn the Differences Between Braking Systems

Share on facebook
Share on twitter
Share on linkedin
Share on email
Share on print
Learn how each braking system works, the benefits, restrictions, regulations, preventative maintenance and more!
Wheelco Mechanic

Drum it down!

What’s the best type of brake for my vehicle? At Wheelco, we get this question a lot. And the answer varies depending on the customer and your needs. So, we’ll break down the benefits, restrictions, regulations, maintenance and more for you.

Drum Brakes 101

This is the grandfather of brakes. Drum braking system has been around for quite some time, and it’s due mostly to their simplistic design and low manufacturing cost.  Not much has changed since it was patented in 1902 because the design is simple and quite simply works!

The drum braking design includes the following components: a backing plate, brake drum, shoe, wheel cylinder and a handful of springs and pins(on hydraulic), or drums ,s-cam and springs, and an air chamber( on air brakes)  All are enclosed within the drum, which simplifies maintenance.

It works by using friction. The shoes or pads press outward against the drum which slows the rotation of the drum. When the drum rotation slows, so does your vehicle.  

Brake Drum Design

This braking system is self-energizing. This means that the rotation of the drum can drag one or both shoes to rub hard against the drum. Therefore, it increases the stopping power. What’s so great about this is that it does this without any additional effort from the driver because it requires less input force, aka hydraulic or air pressure. At Wheelco, we carry all major brands such as Webb, Walther Engineering, Motor Wheel, Gunite, Meritor, and KIC. 

However, it does make the brake more sensitive to brake fade. Due to overheating and repeat use, brake fade can occur. This results in a loss of stopping power. The solution? Replace the brake shoes. At Wheelco, we recommend using CoMan Centers brake shoes. They are affordable, dependable and don’t usually take a lot of time to replace them. Watch CoMan Centers multi-step process to create high quality, new and remanufactured brakes shoes and kits.

Drums are often applied to the rear wheels since most of the stopping force is generated by the front brakes of the vehicle. What does this mean? Less heat is generated in back. Although in some newer trucks 16” drums and wider shoes are being installed on the steer axle to comply with the new RSD rules.

Preventive Maintenance & Key Facts

  • Brake stroke is key measurement during roadside brake inspections. Nearly 1 in 10 vehicles inspected during the Commercial Vehicle Safety Alliance’s annual Brake Safety Week campaign was placed out of service—due to brakes being out of adjustment. Check your slack adjusters by using a small pry bar to move it, checking the brake’s free play. Free play should be between 3/8 and 5/8 of an inch. Free play should be this small across all brakes on a system.
  • Greasing and seals factors into your brake capacity. Putting in less grease than is needed may cause rust and corrosion. Seals inside the cam tube are engineered to let excess grease out of the area.
  • Brake jobs are an important part of maintaining your braking system. If it’s time to do a brake job, don’t forget to check the cam bushings and shims! If the radial play is 0.030 of an inch or more, the cam bushing/camshaft needs to be replaced. Remember that cam bushings are usual a low-cost component that can make a huge difference in your braking performance. Wheelco is proud to carry spring pins and bushings from Triangle Flagg and Dayton Parts.
  • Wear indicator on a caliper/pad assembly should be inspected every four months. With average life expectancy of the products, four or five checks should be made between pad chances.
  • Disc inspection for cracking, a common problem, should be completed regularly.
  • Service intervals for pads, rotors, and adjusters should be done on a regular basis to assess functionality. These procedures vary and can usually be found in the service literature from the manufacturer. For safety and reliability, we offer Meritor, Bendix, Haldex, and Gunite

Brake Drum Advantages

  • Affordable
  • Simple maintenance
  • Self-energizing design
  • Some weight savings from less components in design

Air Disc Brakes 101

As technology progressed, many things got faster and faster—vehicles included. Because of faster speeds, heavier loads and overall demand in performance, the air disc braking system was born. This type of braking systems consists of several parts to include: a metal rotor, brake pads and an air disc caliper.

This braking system works by use of the calipers which squeezes pads against the rotor. Air pressure fills the chamber . A metal piston inside the caliper is then forced against the back of the brake pad. This presses the pad against the spinning rotor, quickly slowing the rotation of the axle. Thus, the speed is reduced.

Compared to drum brakes, disc brakes have better stopping performance and are less prone to brake fade. Additionally, they recover more quickly than S-cam brakes.  

Air Disc Brake Design

Air disc brakes are often referred to as ADBs or disc brakes. They offer an alternate design to the drum braking system. This self-adjusting braking force is proportional to the pressure placed on the brake pad. This gives the driver a better feel and decreases the chances of lockup.

The rotor is usually made of cast iron. However, in many cases, it’s created from a carbon composite. Vanes crafted into the rotors help increase cooling. Eight pistons in the brake calipers provide massive clamping forces. We offer Bendix and Meritor.

Air Disc Brake Advantages

  • Increased stopping power
  • No exaggeration of friction coefficient differences
  • Reduced fade
  • High thermal load
  • Minimal and consistent hysteresis

Reduced Stopping Distance & Regulations

In 2009, the NHSTA amended the Federal Motor Safety Standard on Air Brake Systems (FMVSS No. 121) to improve stopping distances of truck tractors. The launch of the RSD rules does not require air disc brakes. However, air disc brakes superior performance, ease of maintenance and lighter weight make air disc brakes an ideal solution for meeting the new RSD requirements.

Learn all the key facts about Reduced Stopping Distance (RSD), on Wheelco’s RSD Blog Post.

Preventive Maintenance & Key Facts

  • Wear indicator on a caliper/pad assembly should be inspected every four months. With average life expectancy of the products, four or five checks should be made between pad chances.
  • Disc inspection for cracking, a common problem, should be completed regularly.
  • Service intervals for pads, rotors, and adjusters should be done on a regular basis to assess functionality. These procedures vary and can usually be found in the service literature from the manufacturer. For safety and reliability, we offer Meritor and Bendix.

Why Buy from Wheelco Truck and Trailer?

Our brake knowledge is unbeatable. We understand that no two customers are alike, nor are their needs. We offer premium products and popular brands. Tell us what you are driving and we’ll recommend the best braking style for you. 

About Wheelco Truck & Trailer

At Wheelcobeing customer driven is more than just a motto we live by. It means that our employees will do everything we can to best serve you, our valued customer.

Customer driven is more than just offering you advice, giving time-honored service or contributing the latest tech-support. It’s about being there—whenever and wherever you need us—in-person, over the phone or online.

Recent Posts

Video Tutorials

Browse Categories

Follow Us

More to explore

Contact Customer Support

Have a question and want to talk to a human? Get help from one of our a dedicated Customer Service Representative who know the industry. Our team helps customers like you get answers to their unique problems. Get help the way you want - Phone, text chat or email.

Call

(800) 952.3674

Text

Text Wheelco to 797979

Chat

Popup

Email

supportcenter@wheelco.com