What should you do before testing slack adjusters?

Before testing slack adjusters, it is essential to release the parking brakes. This action is crucial because slack adjusters are an integral part of the braking system, and they must be properly engaged to ensure an accurate test. Releasing the parking brakes allows for the necessary movement and operation of the slack adjusters, ensuring they can be assessed effectively.

This step ensures that brake components are functioning correctly and helps in preventing any potential hazards that could arise from testing in an improper state. When the parking brakes are applied, it could interfere with the normal movement of the adjusters, leading to erroneous readings that could misrepresent their condition.

In contrast, driving in reverse, increasing air pressure to maximum, and inspecting brake pads do not directly pertain to the proper procedure for testing slack adjusters. Each of those actions serves a different purpose and does not facilitate the necessary conditions required for a valid assessment of the slack adjusters' functionality.