Brake Slack Adjusters for Commercial Trucks and Trailers
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Slack Adjusters

Slack Adjusters

Brake Adjusters

Slack adjusters (also called brake adjusters or just "slacks") regulate the distance that the air brake has to travel to apply friction to the wheel. This distance increases as use of the brake causes the friction material of the brake shoe to wear away. When the brake is used, the operating rod pushes out on the slack adjuster which then turns the S-cam. The S-cam pushes the brake shoes apart which applies friction and slows the vehicle. Without this function, the air brake can become out of adjustment and the vehicle may lose its capability to slow or stop consistently.

When you need to replace your slack adjusters, it is very important to find the correct part that matches your equipment to ensure a safely operating braking system. It's easy to find the correct replacement slack adjusters for your truck, tractor or trailer. First, the type of slack adjuster should be considered. Slack adjusters are available in two types: manual slack adjusters and automatic slack adjusters.

Both manual and automatic slack adjusters have three qualifications which can be easily measured. Finding these three measurements is the key to finding the correct slack adjusters.

How to Measure and Identify a Slack Adjuster

Spline Teeth

The spline teeth of a slack adjuster fit into the spline teeth of the camshaft. Therefore, the slack adjuster and camshaft must have the same amount of teeth. An easy way to determine the number of teeth is to simply count them.

Spline teeth of a slack adjuster.

Camshaft Diameter

The camshaft diameter is size of the camshaft that fits your particular slack adjuster. This can be found by measuring the inside of the socket or the width of the camshaft.

Camshaft diameter of a slack adjuster

Arm Span

The arm span of a slack adjuster is the distance between the center of the camshaft and the center of the pin hole that is used with the clevis. Many slack adjusters feature multiple pin holes. These slacks can be used at any of the lengths available. For example, a slack adjuster with an arm span of 5.0 and 6.0 inch can be used in applications where a 5 inch or 6 inch arm span is needed.

This picture illustrates the arm span of a slack adjuster.

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