What is the typical specified free travel for a manually adjusted S-cam slack adjuster?

• A. 3/4 To 1 1/4 Inches
• B. 1/2 To 1 Inch
• C. 1/4 To 1/2 Inch
• D. 1 To 2 Inches

Answer: (B)

Free travel is the amount of pushrod movement before the S-cam actually begins to push the brake shoes against the drum. For a manually adjusted slack adjuster on S-cam drum brakes, this clearance must be enough to accommodate shoe wear and thermal changes, yet small enough to ensure quick engagement. The standard specification is 1/2 inch to 1 inch of free travel. Keeping within this range lets the shoes sit clear when released but still bite promptly when you apply the brakes. If free travel is less than 1/2 inch, the brakes can drag or wear unevenly because the shoes are held too tight. If it’s more than about 1 inch, engagement may be delayed, increasing stopping distance. This range best fits the typical maintenance guidelines for these systems.