The first thing to know about a slack adjuster when needing to find a replacement is the brand of the current slack adjuster in your possession.

Spline Count

If you don’t know the part number, pay attention to the number of teeth the slack adjuster contains. The most common is 28, but we see other quantities like 10, 18, and 24. It’s also critical to know whether those teeth are coarse or fine. 

When replacing a slack adjuster, you will need to know the diameter of the spline of the camshaft. The diameter of the hole with teeth on your slack adjuster needs to match the diameter of the spline of the camshaft.

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Clevis Measurement

To measure the distance needed for the clevis, measure from the center of the camshaft hole, up to the mounting pin. Automatic Slack Adjusters can come in various shapes and size, this measurement is how you’re going to clock your slacks when you install the new adjuster.

If the clevis has a clevis pin, take note of what kind it is. Not having the proper clevis can set your brakes up for failure by preventing them from adjusting properly.

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Installation

A slack adjuster will need to be installed at a 90 degree angle either straight up or down. This type of installation creates the proper stroke for your slack adjuster.

Most slack adjuster replacement kits will come with instructions. Follow the instructions to ensure a proper install.

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