How to Adjust Air Brakes

January 27, 2012

It only takes minutes for a driver to manually adjust air brakes and at the same time check for any other brake malfunctions. Be sure you know what you are doing before you begin. You might want to check the air brake CDL manual. Air brakes are not the same as disc brakes. Air brakes are adjusted by manual slack adjusters located on the air canister on the axle housing.

Step 1: Release the Air in the System

Before beginning it is important to chock the tires to prevent the vehicle from moving during the adjustment. While performing the adjustment try to keep each push rod at the same distance in order to keep each wheel's stopping ability close to the same. Make sure that the air brakes system is at full pressure, lower the emergency brake, and push in the air valve releasing the brakes.

Step 2: Check the Push rod

Using a piece of chalk, mark the location on the push rod where it leaves the air chamber. Then using a tool for leverage, pull the push rod out of the brake chamber, and measure from the chalk line to the brake chamber. This will show you the stroke range or how much air must be compressed in order to stop the vehicle. Anything over ¾ of an inch means your brakes need to be adjusted.

Step 3a: Adjusting the Pushrod for Manual Adjusters

Locate the manual slack adjuster near the push rod that you would have checked earlier. Watching the s-cam to see the direction it is turning will help to make sure you are adjusting it correctly and not loosening it. You can tell you are turning it the wrong way if while turning the push rod is pulling out of the air chamber. Once the proper direction has been discovered, continue tightening until you feel it resist. This means you have met the brake linings to the drum. Reverse the adjuster bolt ¼ to ½ turns to maintain a clear distance from the drum to the linings. If for some reason you can turn the manual adjuster bolt in both directions and cannot tell the difference between loosening and tightening, it is time to replace the slack adjuster.

Step 3b: Adjusting the Pushrod for Automatic Adjusters

If you are equipped with automatic slack adjusters, they need no manual adjustment. However, it is still important that you check to make sure proper adjustment is maintained in order to catch brake issues before they happen. If you do make an adjustment of them keep in mind that it will temporarily alter the stroke but eventually the slack will revert to its intended stroke. With automatic adjusters you need to have an air pressure of above 90 psi, have the parking break off and the parking brake control valve and supply valve open. Press the brakes completely and release repeating at least 6 times to test the brakes. This process of air brake test will allow the adjusters to fix themselves if needed. If for some reason you have completed all of these steps and the stroke of the push rod is still excessive, manually adjusting the brakes will only assist in getting you to a repair station.

Related Questions and Answers

Are Air Brake Chambers Only Found on Semi Trucks?

Air brake chambers are found on any vehicle that employs the use of an air brake system. Typically found on large trucks, air brakes were invented, and first used on trains in order to safely stop them. This invention allowed trains to run at faster speeds. Because air brakes are good at stopping heavy vehicles in motion, they are always a part of a large truck's braking system. However, most big rigs also employ the use of a standard brake system in conjunction with the air brake system for added safety.

Where Can I Get an Air Brake Inspection?

Air brake inspection is performed at all truck stop locations. Truck stops are devoted to servicing all of the needs of truckers and their vehicles. Indeed, most of these stops include truck service bays, so qualified truck mechanics can perform inspections and repairs. There are also some other locations that are knowledgeable about air brake systems. These service centers are more commonly found within cities and towns, and include Sun Devil Auto Service, Firestone Complete Auto Care, and AAMCO Transmissions.

Is an Air Braking System Used on Vehicles with Heavy Loads?

An air braking system is always used on vehicles that carry heavy loads. In fact, the air brake system was specifically invented for the railroad, so trains would have a safe and reliable way to stop moving. All trucks used for commercial hauling in addition to vehicles classified as a heavy truck will incorporate an air brake system. Additionally, newer vehicles will also have a standard brake system as back up and support, and may even have anti-lock braking capabilities.

Where Can I Get an Air Brake System Diagram?

An air brake system diagram can be found in all CDL (commercial driver's license) manuals issued by the DMV within that state. Knowledge about maintenance and adjustment is part of the test, and all commercial drivers must know about an air brake system. Additionally, information about air brakes can be obtained online from Wikipedia. An excellent color diagram that points out each component of the air brake system can be found at howstuffworks. Moreover, the link has several parts that will provide an in-depth explanation about air brakes, including their history.

How Many Different Types of Air Disc Brakes are there?

While most air brake systems use drum type brakes, air disc brakes are gaining in popularity. There is only one basic type of disc brake used on vehicles that drive on roadways. Even though the vehicle may have a backup brake system that is very similar to those used in passenger vehicles, these types of brakes are not activated by air pressure. In addition to this alternate braking system, the standard air brake system incorporates a fail-safe program that applies brakes when the vehicle's air pressure is interrupted. Air pressure holds the fail-safe in the off position, and lack of air pressure allows it to become engaged.

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