How To Check Free Play On Manual Slack Adjusters

Manual slack adjusters are an essential component of commercial vehicles, particularly those with air brake systems. They help maintain proper braking performance by ensuring that the brakes are properly adjusted and functioning correctly. One important aspect to consider when inspecting manual slack adjusters is checking for free play.


Free play refers to the amount of movement or “slack” between the brake pedal and the brake shoes or pads. This movement can occur due to wear, damage, or improper adjustment of the slack adjuster. It is crucial to regularly check for free play on manual slack adjusters to ensure that your vehicle’s braking system is functioning optimally.

Step 1: Locate the Manual Slack Adjusters

Before you can begin checking for free play, it is essential to locate the manual slack adjusters on your vehicle. They are typically found on each wheel of a commercial vehicle with an air brake system. The exact location may vary depending on the make and model of your vehicle.

Step 2: Inspect the Slack Adjuster

Once you have located the manual slack adjusters, inspect them for any signs of wear or damage. Look for any visible cracks, corrosion, or debris that may indicate a problem with the adjuster. If you notice any issues, it is important to address them immediately to prevent further damage and ensure proper braking performance.

Step 3: Check for Free Play

To check for free play on manual slack adjusters, follow these steps:

  1. Start the engine and apply the parking brake.
  2. Depress the brake pedal several times to build up air pressure in the system.
  3. Release the parking brake and depress the brake pedal again. Observe any movement or “slack” between the pedal and the brake shoes or pads.
  4. If you notice excessive free play, it may indicate that the slack adjuster needs to be adjusted or replaced. Consult your vehicle’s maintenance manual or a qualified mechanic for further guidance on how to address this issue.


Regularly checking for free play on manual slack adjusters is crucial in maintaining the proper functioning of your vehicle’s braking system. By following these steps, you can ensure that any issues are detected early and addressed promptly, ensuring safe and efficient driving conditions.