CAMS

Cams For Peterbilt Trucks

S-cam shafts are a fundamental component of the air brake foundation brake system on Class 8 Peterbilt trucks. The S-cam converts the linear push of the brake chamber pushrod into rotational force that spreads the brake shoes against the drum. Worn or corroded S-cams lead to uneven brake application, excessive shoe wear, and potential out-of-service violations during roadside inspections. We carry S-cam shafts, cam bushings, and related hardware for Peterbilt drive and trailer axle configurations.

Frequently asked questions about cams

How do I know if my S-cam needs to be replaced?

Worn S-cam lobes cause the brake shoes to contact the drum unevenly, resulting in brake pull, premature shoe wear on one side, and reduced stopping performance. During a brake inspection, check the cam for pitting, corrosion, and wear on the S-profile contact surfaces. Excessive lateral play in the cam shaft — typically more than 0.030 inches — indicates worn bushings that should be replaced along with the cam.

Should I replace cam bushings at the same time as the S-cam?

Almost always yes. Worn cam bushings allow the cam to move laterally and rock in its bore, which accelerates wear on both the cam and the spider assembly. Since the cam has to come out to replace the bushings anyway, it's standard practice to replace both together. Greasing the cam shaft and bushings at every PM interval significantly extends service life.

Are S-cams handed (left and right specific)?

Yes. S-cams are directional — the left-hand and right-hand cams for a given axle position are mirror images of each other. Installing a cam on the wrong side will cause the brakes to apply in the wrong direction, resulting in severely degraded or absent braking force on that wheel end. Always confirm hand (LH or RH) and axle position when ordering replacement cams.

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