5.1.15 – Parking Brake Controls In newer vehicles with air brakes, you put on the parking brakes using a diamond-shaped, yellow, push-pull control knob. You pull the knob out to put the parking brakes (spring brakes) on, and push it into release them. On older vehicles, the parking brakes maybe controlled by a lever. Use the parking brakes whenever you park. Caution. Never push the brake pedal down when the spring brakes are on. If you do, the brakes could be damaged by the combined forces of the springs and the air pressure. Many brake systems are designed so this will not happen. But not all systems are setup that way, and those that are may not always work. It is much better to develop the habit of not pushing the brake pedal down when the spring brakes are on.