How To Adjust Slack Adjusters On A Semi Trailer

Slack adjusters play a crucial role in the functionality of semi trailers by ensuring the brakes work effectively and reducing undue strain on the braking system. In this article, we’ll explain the correct method for adjusting slack adjusters on a semi trailer.


Before beginning any work on your semi trailer’s brake system, it is important to ensure that the vehicle is parked on a level surface and that the engine is turned off. Additionally, make sure that you have all necessary tools and equipment on hand before starting the adjustment process.

Step 1: Locate the Slack Adjusters

The first step in adjusting slack adjusters is to locate them. Slack adjusters are typically located near the brake drums on each wheel of the trailer. They are usually mounted on a bracket or frame member and can be identified by their distinctive shape.

Step 2: Measure the Existing Adjustment

Once you have located the slack adjusters, use a tape measure to determine the current adjustment. This will give you a baseline for making any necessary adjustments.

Step 3: Loosen the Locknut and Adjust the Slack Adjuster

Using a wrench, loosen the locknut on the slack adjuster. This will allow you to make adjustments to the brake system. Once the locknut is loose, use a ratchet or other tool to turn the slack adjuster until the desired amount of tension is achieved.

Step 4: Tighten the Locknut

Once you have made the necessary adjustments to the slack adjuster, use a wrench to tighten the locknut. Make sure that it is securely in place and will not come loose during normal driving conditions.

Step 5: Test the Brakes

After making any adjustments to the slack adjusters, it is important to test the brakes to ensure that they are functioning properly. Drive the trailer at a safe speed and apply the brakes gradually. Listen for any unusual noises or feel for any vibrations in the pedal.


In conclusion, adjusting slack adjusters on a semi trailer is an important maintenance task that should be performed regularly to ensure proper brake function and prevent excessive wear on the brake system. By following these simple steps, you can easily adjust your own slack adjusters and keep your trailer running smoothly.