The Functions and Significance of Slack Adjusters

Automatic Slack Adjuster

The Functions and Significance of Slack Adjusters

The air brake system on your semi-truck has a complicated array of moving parts. It’s usually made up of hundreds of parts, including slack adjusters. If you own a semi-truck, you most likely have an air brake system with slack adjusters. Slack adjusters are lever arms that are connected to the push rod of the brake chamber, which is located in the clevis assembly. These are an essential component of your heavy-duty truck’s air brake system, despite being only one small piece of the larger puzzle.

 Simply put, slack adjusters are the mechanical link between the push rods in the brake chamber and the camshaft. As the brakes are applied or released, the entire slack adjuster rotates with the camshaft. As a result, the slack adjuster needs to be maintained and checked regularly.

 Slack adjusters adjust the brakes to compensate for lining wear. When you apply the brake, a rod pushes the slack adjuster out. The slack adjuster then turns the s-cam, causing the brake shoe to separate. The mechanism then applies the force required to stop a truck. In this way, slack adjusters in vehicles are designed to serve three distinct functions.

  • To begin, modern slack adjusters are designed to convert the push rod’s forward, linear motion into the rotary motion of the camshaft.
  • They also function as a lever for generating force and directing it to the brake discs.
  • Finally, they reduce the distance between the brake shoes and the brake drum, enabling drivers to experience more responsive braking.


Slack adjusters are available in a variety of arm lengths, configurations, torque ratings, and spline types. These are available for all kinds of trucks. However, there are typically two types of slack adjusters: self-adjusting and automatic slack adjusters.

Automatic slack adjusters automatically keep breaks in the proper adjustment. They are designed in a way to compensate for brake lining and maintain a constant actuator stroke. These adjusters are required to be regularly checked so they maintain proper push rod travel. There is no need to make any manual adjustments with automatic slack adjusters.

When looking for slack adjusters, one should opt for reputed brands like Haldex slack adjusters. However, these slack adjusters have a finite life expectancy, and they are often required to be replaced after four or five years of use. Today, many reputed online stores offer quality slack adjusters from well-known brands at reasonable prices.