Final answer:
To check the free play of manual slack adjusters on S-cam brakes, one must park the vehicle on a flat surface to ensure stability and safety during the inspection.
Step-by-step explanation:
To check the free play of manual slack adjusters on S-cam brakes, the correct answer is that you should park on a flat surface. A flat surface ensures that the vehicle is stable and does not roll, which could affect the accuracy of your brake adjustments and safety during the inspection.
It is also important to chock the wheels to prevent any movement. Checking the free play is crucial for maintaining the proper function of brake systems in heavy vehicles like trucks and buses. It is part of regular preventive maintenance to ensure the brakes engage and release appropriately, maintaining safe stopping distances.