How To Check Slack Adjusters On Air Brakes

Air brakes play a vital role in the operation of commercial vehicles by providing a secure and dependable way to stop. It is important to note, like any other mechanical system, air brakes need routine upkeep in order to operate effectively. Keeping a close eye on the slack adjusters is a critical part of properly maintaining air brakes.


Slack adjusters are devices that help regulate the distance between the brake shoes and the drum, ensuring proper braking performance. They play a vital role in maintaining the correct amount of “slack” or free movement within the brake system. Over time, slack adjusters can become misaligned or damaged, leading to decreased braking efficiency and potential safety hazards.

Step 1: Inspect the Slack Adjuster

The first step in checking slack adjusters is to visually inspect them. Look for any signs of wear, damage, or corrosion on the slack adjuster housing and components. Pay close attention to the threads, as they can become stripped or damaged over time. If you notice any issues, it may be necessary to replace the slack adjuster entirely.

Step 2: Measure Slack Adjustment

Next, measure the amount of slack in the brake system by turning the slack adjuster until you feel resistance. Use a ruler or tape measure to determine the distance between the brake shoe and the drum. The exact measurement will depend on your vehicle’s specifications, so refer to the manufacturer’s guidelines for the appropriate range.

Step 3: Adjust Slack Adjuster

If the slack adjustment is within the acceptable range, you can proceed with adjusting the slack adjuster. Turn the slack adjuster until it reaches the desired measurement. It’s important to note that over-adjusting the slack adjuster can lead to premature wear and damage to the brake system.

Step 4: Test Brake Performance

After making any necessary adjustments, test the brake performance by applying pressure to the brake pedal. The brakes should engage smoothly and with adequate force. If you notice any issues or inconsistencies, it may be necessary to further inspect and troubleshoot the brake system.


Regularly checking and maintaining slack adjusters on air brakes is crucial for ensuring safe and reliable braking performance. By following these steps, you can effectively inspect, measure, adjust, and test your vehicle’s slack adjusters, helping to prevent potential hazards and extend the lifespan of your brake system.