5 Key Components of an Air Brake System in Trucks - MPC

16 Jun.,2025

 

5 Key Components of an Air Brake System in Trucks - MPC

If you’re managing a fleet that includes heavy trucks and buses, then you know exactly how much hard work it takes to guarantee that every component of these vehicles is working at optimal capacity. You surely employ a group of great drivers and keep an elite group of mechanics on your roster – perhaps you have even adopted a fleet tracking system to keep track of the movement, service appointments, and important warranty information that applies to these pricey assets.

With competitive price and timely delivery, ALLMAX sincerely hope to be your supplier and partner.

But, just because you’ve taken steps to follow smart hiring practices and invest in automation doesn’t mean that all of your bases are covered.

Take the issue of air brake systems, for instance. Most managers and drivers have a general understanding of how these specialized friction brakes work, but not enough fully grasp the true mechanics of this important safety system. 

To correct this, take the time to read through our list of the 5 basic components of elementary air brake systems.

Remember, the clearer your understanding on this topic, the better informed you will be when forced to make big decisions regarding your fleet.

1. Air Compressor

An air compressor maintains the proper level of air pressure so that the air brakes and any other air-powered accessories operate safely and consistently.

Depending on the make and model of your heavy truck, its compressor is either gear or belt-driven and gets cooled by either air or an engine cooling system. The compressor(s) startup every time the engine is triggered, and the device loads and unloads air which is pumped in and out of the reservoirs and the other two-cylinder compressors.

Maintenance Tip: If the air compressor’s temperature is governed by an engine cooling system, it may have its own, separate oil supply. If this is the case, ensure that the operator and/or designated fleet team mechanic check the compressor’s oil levels before the truck hits the road.

Additionally, many compressors have their own filtration system, which also must be serviced on a regular basis.

2. Reservoirs 

In the case of heavy truck and bus air brake systems, it’s the reservoirs that hold onto a sufficient amount of compressed air, until the supply is required for braking. Note: drivers cannot control the amount of air that they use when the air brakes are triggered; the amount solely depends on how much has been circulated by the compressor.

In terms of design, reservoirs are pressure-rated tanks that feature special drain valves called draincocks. When the draincocks are in the ‘open’ position, they drain themselves of any moisture or pollutants that might compromise the integrity of the air.

Maintenance Tip: In order to guarantee that your reservoirs are in top shape, each must be drained entirely at least once a day when in service.

Are you interested in learning more about heavy duty truck brake lining? Contact us today to secure an expert consultation!

The foot valve, otherwise known as the treadle or the brake pedal, is the tool that determines the volume of air pressure used. In this case, the volume is determined by how hard the operator presses their foot on the foot valve.

When the compressed air is released through the brake system, it takes time for it to be produced again through the compressor function (described above). That said, if too much pressure is released in a short period of time, the entire system could fail.

Maintenance Tip: Supply your operators with proper training of the air brake system before they are allowed to join your team. If they are not properly educated on brake maintenance (i.e., they press and release the brakes often and unnecessarily) the air brake system can incur permanent damage.

4. Brake Chambers

Brake chambers, otherwise known as brake pots, are the devices that turn the compressed air into mechanical force. It is through this mechanism that the brakes are triggered and the heavy truck or bus is able to safely halt.

Each one of the brake chambers comes equipped with a specific pushrod stroke adjustment limit. The chamber itself is held together by a clamp assembly that is specially made to regulate the compressed air that is released into the chambers.

Maintenance Tip: Regular maintenance must be performed directly to the brake chambers as dictated by the truck’s manual. This required maintenance is to guarantee that the pushrod stroke is operating within normal range. If this maintenance is not performed, the entire air brake system could fail.

5. Brake Shoes and Drums

By making use of friction, the brake shoes – or pads, depending on the make and model of the truck – are forced outwards, thus initiating the air brake system.

A special brake lining material is attached to the brake shoes to help promote consistency. If the type of lining is a good fit, it should also regulate heat that is created from the friction.

Maintenance Tip: Always replace the aforementioned lining when necessary. Also, make sure that your mechanic frequently services other possible over-worked areas. These issues include distorted drums, poor adjustment, or dirty linings.

Final Thoughts on Air Brake Components

Understanding the critical components of an air brake system is essential for maintaining the safety and efficiency of heavy trucks and buses.

The five fundamental elements include

  • The air compressor, which ensures adequate air pressure for the brakes and other air-powered accessories
  • The reservoirs that store compressed air until needed for braking
  • The foot valve, or brake pedal, which regulates the amount of air pressure applied based on the driver’s input
  • The brake chambers that convert compressed air into mechanical force to activate the brakes; and the brake shoes and drums that utilize friction to slow down or stop the vehicle

Regular maintenance of these components is vital to prevent system failures and ensure optimal performance.

The company is the world’s best Truck Brake Pads manufacturer supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

difference of high vs low cost brake linings - Truckers Report

Most of the time the cost difference between brake linings on the same style shoe is due to the weight rating of the axle braking capacity.

The cheaper shoes will have a weight rating of 20,000 Lbs. The higher price shoes will usually have a weight capacity of 23,000 Lbs. The higher weight capacity will stop the truck faster with less applied air pressure to the braking system, but will also have a higher coefficient of friction. The higher friction capacity of the 23,000 lb shoes will wear the brake drums faster and usually means that you'll have to purchase new drums at the next brake job. I always run the 23,000 Lb brake shoe for the fact that I can stop in a shorter distance than I can with the 20,000 Lb shoes in an emergency situation. You also don't want to mix and match these shoes on the same axle...........you really don't want to mix and match them on the same truck in my opinion. The 20,000 lb shoes can be found easily on the road if you have a break down and need new shoes quickly. Most on road/on call service repair shops won't carry the 23,000 lb shoes.
There's a trade off. With better linings come increased drum wear. Something has to wear when you are dealing with friction. But the ability to handle heat is better, thus reducing glazing and fade and increased effectiveness.

According to the NHTSA and their tests, OE (original equipment) linings will out perform AM (after market) significantly.
Maintenance issues play a big role on how long they will last too. Not properly adjusted or a rough drum will wear them out quicker.

Does it say Made in China on the box?
They definitely stop faster and since I usually replace the drums anyway the added wear isn't a big deal. You can tell the difference immediately, they grab hard. But like Mr.Haney said I wouldn't mix and match, I did by accident. Put the better shoes (grade 5's i believe) on one side of an axle and abex on the rest of the trailer. The wheels with the better shoes would lock up.

If you want to do some reading this is kind of interesting. It's an "S-Cam Brake Effectiveness Comparison
Using Two Fixtures and Two Lining Types on a Single Inertia Dynamometer"
...and if the cheap shoes had enough friction to lock the brakes how exactly would more expensive shoes have helped?