In an S-cam drum brake system, which component is directly moved by the push rod as air pressure acts on the brake chamber?

In an S-cam drum brake system, which component is directly moved by the push rod as air pressure acts on the brake chamber?

• A. brake camshaft
• B. slack adjuster
• C. push rod
• D. drum

Answer: (B)

When air pressure acts on the brake chamber, it moves the piston, which pushes on the push rod. That push rod directly engages the slack adjuster, transferring the force. The slack adjuster then converts this linear motion into rotation that turns the S-cam, pressing the brake shoes outward against the drum. So the component directly moved by the push rod is the slack adjuster. The brake camshaft is driven by the slack adjuster, not directly by the push rod, and the drum itself isn’t directly moved by the push rod—it’s the shoes pressing against it that creates braking.

When air pressure acts on the brake chamber, it moves the piston, which pushes on the push rod. That push rod directly engages the slack adjuster, transferring the force. The slack adjuster then converts this linear motion into rotation that turns the S-cam, pressing the brake shoes outward against the drum. So the component directly moved by the push rod is the slack adjuster. The brake camshaft is driven by the slack adjuster, not directly by the push rod, and the drum itself isn’t directly moved by the push rod—it’s the shoes pressing against it that creates braking.