A commercial driver is conducting a comprehensive pre-trip mechanical inspection of an S-c… — Commercial Driver's License (CDL) General Knowledge Exam

A commercial driver is conducting a comprehensive pre-trip mechanical inspection of an S-cam air brake assembly at a drive-axle wheel position. Arrange the following inspection actions into the correct procedural sequence from initial preparation to final friction surface assessment.

1Chock the vehicle wheels on level ground and release the parking brakes from the cab to remove spring brake tension.
2Inspect the brake chamber mounting bracket, fasteners, and flexible air supply lines for physical damage, loose hardware, and audible air leaks.
3Place a distinct chalk reference mark on the pushrod where it exits the brake chamber body while the brakes remain fully released.
4Use a pry bar to pull firmly on the manual slack adjuster and measure the distance between the reference mark and the chamber face to confirm pushrod free play is no more than $1\text{ inch}$ .
5Inspect the brake drum and friction linings through the dust shield opening to verify that lining thickness is at least $\frac{1}{4}\text{ inch}$ and free of grease or oil contamination.

Answer

The correct sequence begins with chocking the wheels and releasing the parking brakes, followed by inspecting the brake chamber and lines, placing a chalk mark on the pushrod, pulling the slack adjuster with a pry bar to verify no more than

1\text{ inch}

of free play, and concluding with inspecting the brake drum and lining thickness for defects and oil contamination.

A thorough wheel-end brake inspection must follow a logical safety and mechanical progression. The vehicle must first be secured with wheel chocks so that the parking/spring brakes can be safely released. Next, the outer chamber and air lines are checked for structural integrity and leaks. A baseline chalk mark is then placed on the pushrod at rest, allowing the inspector to pull the slack adjuster with a pry bar and measure free play against the

1\text{ inch}

standard. Finally, internal foundation components (brake drum and linings) are inspected to ensure adequate thickness (at least

\frac{1}{4}\text{ inch}

) and absence of lubricant contamination.

Step-by-Step Solution

Chock the wheels and release the parking brake in the cab.

The vehicle is physically prevented from rolling and the spring brakes are disengaged from the foundation brake components.

Spring brakes hold the pushrod and slack adjuster rigidly in place; releasing them is required to check mechanical free play.

Examine the brake chamber, mounting bracket, and air hoses.

External structural security and pneumatic line integrity are confirmed.

Ensures the chamber will not shift or leak during operation and manual linkage testing.

Mark the pushrod at the brake chamber face with chalk or a grease pencil.

A zero-point baseline reference is established at rest.

A reference mark is necessary to accurately measure the distance the pushrod travels when pulled.

Pull the slack adjuster with a pry bar and measure pushrod displacement.

Manual slack adjuster free play is verified against the maximum legal limit of

1\text{ inch}

(

25.4\text{ mm}

Excessive free play indicates out-of-adjustment foundation brakes or worn clevis pins and bushings.

Inspect the friction linings and drum surface through the backing plate / dust cover opening.

Friction lining thickness is verified to be

\ge \frac{1}{4}\text{ inch}

and clean of oil or grease from hub seal failure.

Directly checks friction material serviceability and ensures structural drum integrity.

Key Concept

Step-by-step foundation air brake mechanical inspection and slack adjuster free-play measurement protocol.

Estimated Time:1m 30s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic