How to Set Air Brakes

Large vehicles like semi trucks and buses contain a braking system called air brakes. Setting the air brakes is an integral part of being a good driver, as you are responsible for properly maintaining your braking system. Hopefully, you will be able to have them set and inspected at the shop before your trips. However, the air brakes should be adjusted every day during your pre-trip inspection while you are out on the road.

Things You'll Need

• Flashlight
• Chalk
• Ruler
• Pry bar
• Wrench
• Protective gear (hard hat, eye protection)

Instructions

1. Make sure your brakes are fully adjusted in the shop before you start out on a trip. The vehicle should be suspended off the floor, so you (or the mechanic) can make the adjustments with the wheels off the ground. Getting things in tip-top shape before heading out is always a good idea.

2. Park your vehicle in a safe spot, and block the wheels.

3. Bring the air system to full pressure (at least 100 psi).

4. Release all parking brakes.

5. Turn the engine off, and listen carefully for audible air leaks. Turn the engine back on and bring it back to full pressure (at least 100 psi).

6. Mark with chalk where the pushrod comes out of the brake chamber.

7. Use a pry bar for leverage to pull the pushrod out of the brake chamber.

8. Measure with a ruler the distance between the chalk mark you made in Step 6 to the face of the brake chamber. Correctly adjusted brakes should have no more than 1/2 to 3/4 inch of slack available.

9. Press the locking sleeve in with a wrench, making an adjustment if necessary. Tighten the slack adjustment by turning the adjusting bolt and making sure the camshaft is rotating in the direction of brake application.

10. Repeat Steps 5 to 8 to verify that the adjustments made were correct.