With S-cam drum brakes, when the brake chamber fills with air, air pressure pushes the push rod out, moving the ___ and thus rotating the _____?

With S-cam drum brakes, when the brake chamber fills with air, air pressure pushes the push rod out, moving the ___ and thus rotating the _____?

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

Answer: (C)

When air fills the brake chamber in S-cam drum brakes, that pressure pushes the push rod outward. The push rod then drives the slack adjuster, which converts that linear motion into rotation of the S-cam brake camshaft. As the cam rotates, it pushes the brake shoes outward against the inside of the drum, creating the friction needed to slow the wheel. The other options don’t fit because the push rod doesn’t move the brake drum or wheel directly, and the camshaft is rotated by the slack adjuster, not the other way around.

When air fills the brake chamber in S-cam drum brakes, that pressure pushes the push rod outward. The push rod then drives the slack adjuster, which converts that linear motion into rotation of the S-cam brake camshaft. As the cam rotates, it pushes the brake shoes outward against the inside of the drum, creating the friction needed to slow the wheel. The other options don’t fit because the push rod doesn’t move the brake drum or wheel directly, and the camshaft is rotated by the slack adjuster, not the other way around.