CEG Industry Blog

BLOG: 10 Important Facts About Truck Air Brakes

Ease up on your truck air brakes as we go over some key points.

📅   Wed November 02, 2016 - Edition
Jurica Magoci - CEG BLOGGER

Spring brakes, truck air brakes and all different types of brake systems are sturdy, durable, designed to give the best stopping assistance possible.
Spring brakes, truck air brakes and all different types of brake systems are sturdy, durable, designed to give the best stopping assistance possible.

Before you slam on your truck air brakes, you might want to read this first: I have said it many times before and will continue to do so. Being a truck driver; choosing the endless roads as a lifestyle and being part of the trucking industry is a great experience. There are so many aspects related to this career field that you simply can't find anywhere else! Oh sure it isn't always peaches and cream, but what is? So what are some of the good things about being an OTR Driver?

• Independence, traveling the open road and setting your own basic schedule

• Interaction, you get to interact with people from all over the country

• Freedom, not being stuck dealing with lots of people or office politics

Not everyone is cutout for this lifestyle. Neither all those things are bad. There are many people who really enjoy working around all the different personalities. Some thrive and excel in that environment, and that too is great.

What is the downside to the trucking? -Well besides ever changing laws and regulations, operating in all types of weather, other drivers and to be honest there are other things, but, that is true for every industry. Of course each industry has its own individual concerns. One such concern specific to the trucking industry is the driver CDL requirements and necessary endorsements (depending on the freight to be hauled).

You, or your drivers, will be required to obtain a Commercial Driver's License (CDL). In addition to this, recording to Occupational Safety and Health Administration OSHA, your company and the drivers who operate your trucks will be required to pass additional truck operator training and get the appropriate endorsements. Be prepared you may need to actually pass test to receive these additional endorsements. State level testing requirements will vary, but here is a list of federal endorsement codes that might be required according to DMV.ORG:

• H Endorsement: for vehicles transporting any hazardous materials.

• N Endorsement: for vehicles hauling or drivers operating tank vehicles.

• P Endorsement: for vehicles with passengers (requirements depend on your state)

• S Endorsement: for the operation of school bus (other requirements may apply).

• T Endorsement: for towing a double or triple trailer (other endorsements may apply).

• X Endorsement: for operating both HAZMAT and tank vehicles.

Besides these endorsements there are restrictions. These will keep you from being able to operate some vehicles or transport certain loads based on the restriction. We will discuss these another time. However, there is one endorsement that will be required for sure, the CDL brake test.

Like most things associated with this industry, this is geared towards safety (and you want a good safety rating). The Federal Motor Carrier Safety Administration (FMCSA) require testing to ensure both driver and company is in compliance with safety related rules and regulations.

Ok, so ease up on your truck air brakes, as we go over some key points.

1. Why is Truck Air Brakes Testing Important?

As stated this is required by the FMCSA. It shows that the operator/driver has passed the required trucks air brakes testing. It will also be on your/their driver's license. When as by law enforcement every commercial truck driver must show proof and present this information.

Remember this is not just about some government rule designed to fleece more revenue from the industry. There is very real issue to be concerned with. Drivers must know how to properly and safety apply their truck air brakes. Imagine trying to stop a several ton vehicle (just think how long it takes a fast moving train to stop). Now imagine a driver, who wasn't properly trained, trying to stop on an icy road!

2. What is Truck Air Brake Testing?

Well, in general this is much like any other test. Your knowledge, driver skills, and proficiency will be measured to see if you understand and can properly engage the truck air brakes. As a commercial truck driver you must be able to know when and how to correctly use them. They will test this both in written form and a practical use.

In order to pass the CDL test you will need to demonstrate the following:

1. Properly engage and disengage the truck's parking brake

2. Properly engage and disengage the truck's hydraulic brakes

3. Check the truck air brake for air leakage

4. Check the air warning alarm

5. Check the spring brakes activation

6. Check the buildup rate for the air compressor

7. Check the shut-off system for the Air Compressor

8. Ensure the spring break will automatically disengage

9. Properly engage and disengage the truck's service brakes

Additionally your knowledge will be tested on:

• How well you know the truck air brakes various components

• You're knowledge of the truck air brake connections

• Your overall knowledge and performance engaging/disengaging them

• How to properly perform a pre-trip truck air brakes inspection

One other thought, you must receive a score of 80% or you will fail the test.

3. Something to be aware of when it comes to Truck Air Brakes

This might seem like a common knowledge thing, and perhaps it is. But there is a big difference between operating vehicles with hydraulic braking systems and air braking systems. Air, or more correctly, air pressure is what allows your truck air brakes to operate properly. If the pressure is weak the brakes won't engage properly.

Imagine being on that icy road without truck and trailer brakes! That can be a scary thought, especially if you're heading downhill in some of the most dangerous roads for drivers, like: the Ozarks or the Rocky Mountains. Often air will bleed out of your brakes and it might take a little time to build it back up. That is fine; don't risk trying to drive off without proper pressure.

4. How do you Test your Truck Air Brakes?

This is very important and is something that should have been taught prior to getting your truck air brakes endorsement. But it might have been a while since you tested. Perhaps you work at a place where the mechanic does all the truck air brakes testing. So here are some basic steps for testing your trucks air brakes.

1. The first thing is your seatbelt, buckle up for safety!

2. After starting your truck build up the pressure (90-110 lbs)

3. Check your parking brake by, applying the parking brake, shift into gear, releasing the clutch and attempting to move, it should not.

4. Charge your truck's air system

5. Allow the airlines to fill

6. It will take about a minute to be able to check for leaks, (no more than 2 psi)

7. Apply 90 pounds of pressure and hold for about one minute

8. 3 psi should be the maximum leakage

9. Pumping the brakes, should cause the light/alarm to activate (at about 60 pounds)

10. If you keep pumping, the truck's protection valve should pop out (20 to 40 psi)

11. Running and in neutral check to see how long it takes for the pressure to build back up (should build to between 85 and 100 psi)

12. As the pressure builds the air governor should blow out (between 125 and 130 psi).

5. You will want to Practice the Truck Air Brakes Steps

Just like anything else in life, it will take practice to get proficient in testing your truck air brakes. It isn't really that difficult, if you have spent any time at all around commercial vehicles. If you have been driving you should have a good idea how they work and should operate. If you are relatively new in trucking business, the hard part is learning all the steps. Though others will say it's the waiting between steps.

So don't worry if you need to try it a few times while sitting in the yard. The last thing you will want to have happen is be out in the middle of nowhere, having an issue and not be able to check it. It does take a little time but ask yourself: “Is it better to lose you time or fail when taking the test?” –Practice, and practice and practice….. That is all you need to do.

6. What if there is an Issue During the Truck Air Brakes Test?

Well, first don't “what if” yourself to death. Just relax. After all you have sat out in that yard and practiced this like a hundred times. Repetition is the key to learning anything, the more you do the better. This is where muscle memory comes in, if practiced enough it will be like second nature.

Now if there are any issues though don't fret. Relax breath, and just go through the motions, exactly like you practiced a million times. Remember it is ok to tell the instructor that you need to start again. They might or might not be understanding, that doesn't matter; it is your right during the truck air brakes test to start again. Once you say you are finished and they lock in your score that is it. If you feel you should try again, go and do so.

7. The Truck Air Brakes Compressor

This is one of the key components of the truck air brakes system. It is what pumps air into the tanks (air storage tanks/reservoirs). Sometimes the compressor is air cooled other times systems are actually hooked into the truck's cooling system. Another point, you might need to check compressor oil levels, if it isn't tied to engine.

The air compressor is controlled by the governor, controlling when air is pumped into the reservoirs. Around 125 pounds per square inch (psi) the governor will stop the compressor from pumping air. When the pressure drops to about 100 psi the compressor will cut-in and start pumping air again.

8. The Truck Air Brakes Reservoir

The reservoirs are used to hold the compressed air. Every model of truck can be different, the size and number of tanks will vary. The tanks should be big enough to allow the vehicle to stop several times before going empty. This is a safety feature just in case there was a malfunction with the compressor.

Water and oil can build up in the air tanks. This can be really bad for the truck air brakes. The water can freeze up in the winter time, causing your truck air brakes to fail. This usually collects at the bottom of the reservoir. Fortunately the air tanks are equipped with drain valve. Be sure to drain the oil and water out completely.

9. The Truck Air Brakes Brake Pedal

This is another one of those things you should already know. But I feel it is important to cover. The brake pedal (also known as the foot valve or treadle valve) is obviously what one uses to engage the brakes. However, what some don't understand is how to properly engage you truck air brakes. You should refrain from slamming them on.

The harder you press the brake applies more pressure. Of course the opposite is true when releasing the brakes. Remember though this also lets compressed air out of your system, reducing the reservoir amount. This is what the compressor does, it replenishes the used air. Pumping the brakes repeatedly causes the air to escape faster than it can be replaced. Once the pressure drops to low your truck air brakes won't operate (you won't be able to stop).

10. Some other Truck Air Brakes Facts

The components of the truck air brakes are what make up the entire braking system.

Basically they are the:

• Linings

• Drums and

• Shoes

The drum is what houses the braking mechanism. So when the truck air brakes are engaged the lining and the shoe get pushed against the inside wall of the drum. The resulting friction is what slows or stops the truck.

Remember to drum is designed to take a lot of heat, and that comes from engaging the truck air brakes. The exact amount of heat really depends on the drum (manufacturers vary). But it also depends on how hard and long the brakes were applied for. If too much heat were to build up the brakes would stop working, and no one wants that!


Though this is an exciting and wonderful career to be a part of, there are issues and things to know. Some just come with practice and time. Experience can truly be the best teacher. But there are also things which you must understand and learn right away. All the best truck drivers will tell you they never stop learning!

Spring brakes, truck air brakes and all different types of brake systems are sturdy, durable, designed to give the best stopping assistance possible. The average truck weighs several pounds; add a heavy load and it can take a lot to stop. So, never underestimate the importance of your truck air brakes, they are one of the most important truck equipment.

Do you have a brand you prefer? Ever have you brake bleed out while out on the road? What did you do in that case? If you have any tips, questions, and/or suggestions please share.

As I said the best professionals are always learning and updating their skills!