SLACK ADJUSTERS & COMPONENTS

Slack Adjusters & Components For Peterbilt Trucks

Slack adjusters are the mechanical link between the brake chamber pushrod and the S-cam shaft — they convert the linear stroke of the chamber into the rotational force that applies the brakes, and they compensate for brake lining wear to maintain proper pushrod travel. Automatic slack adjusters (ASAs) are required on all commercial vehicles and self-adjust to keep pushrod stroke within limits as linings wear. A slack adjuster that's out of adjustment or failing is one of the most common causes of brake-related out-of-service violations. We carry automatic slack adjusters, manual slack adjusters, and related hardware for Peterbilt trucks.

Frequently asked questions about slack adjusters & components

If I have automatic slack adjusters, why do my brakes still need adjustment?

Automatic slack adjusters maintain adjustment during normal brake application and release cycles, but they cannot compensate for a brake that's been manually backed off, for a worn clevis pin that introduces play in the linkage, or for a slack adjuster that's failed internally. An ASA that repeatedly requires manual adjustment is not doing its job — it should be replaced rather than continually re-adjusted. Repeated manual adjustment of an ASA is a sign of a failed unit, not a maintenance procedure.

How do I measure pushrod stroke to check slack adjuster adjustment on a Peterbilt?

With the brakes fully released and system air pressure at operating level, mark the pushrod at the brake chamber face and apply approximately 90 PSI to the brakes (or have a helper hold the foot valve down). Measure the distance the pushrod travels from the released to applied position. For most Type 30 chambers, the maximum allowable stroke is 2 inches — anything over that is an out-of-adjustment condition and an FMCSA out-of-service violation if found during roadside inspection.

What's the difference between a standard and a long-stroke slack adjuster?

Standard slack adjusters are designed to work with standard-stroke brake chambers, where maximum applied stroke is typically 1.75–2.0 inches. Long-stroke slack adjusters are paired with long-stroke chambers (Type 30L, 24L, etc.) that have a maximum stroke of 2.5 inches and provide greater clamping force for heavy-duty axle configurations. Mixing standard and long-stroke components is a common installation error — the slack adjuster and chamber stroke rating must be matched to ensure correct adjustment range and safe brake performance.

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