How To Adjust Air Brakes

Air brake adjustment is crucial for maintaining the performance and safety of heavy-duty vehicles. The exact procedure can vary depending on the brake chamber type and size, so it’s essential to understand your specific vehicle’s system before beginning. Here’s a step-by-step guide for adjusting air brakes, with tips to ensure optimal performance.

Key Steps for Adjusting Air Brakes:

1. Prepare Your Tools To perform a manual adjustment, gather the necessary tools: a wrench, marker or chalk, flashlight, and a pry bar (optional). Safety gear like work gloves, protective eyewear, and a bump cap are also highly recommended as you’ll be working under the vehicle.
2. Secure the Vehicle Always begin by securing the vehicle to prevent movement. Place wheel chocks and ensure the vehicle is in low gear before turning off the engine.
3. Check Air Pressure Use the air pressure gauge on your dashboard to verify the system’s air pressure. The pressure should be between 90-100 psi before releasing the parking brakes.
4. Mark the Pushrod Using chalk or a marker, make an accurate mark on the pushrod where it exits the brake chamber. This will help in tracking the pushrod’s movement during adjustment.
5. Measure the Slack Pull the pushrod out (either by hand or with a pry bar) and measure the distance between your mark and the brake chamber. On a standard Type 30 brake chamber, the slack should not exceed ¾ inch. If it does, an adjustment is necessary.
6. Check for Warning Indicators Some vehicles feature red marks on the pushrod to signal when an adjustment is required. If this marking is visible, an immediate brake adjustment is needed.
7. Disengage the Locking Device Use a wrench to disengage the external locking device on the manual slack adjuster. Be careful not to damage the lock while doing so.
8. Adjust the Bolt Turn the adjustment bolt to regulate the slack. Be sure to turn the bolt in the correct direction: turning it clockwise will pull the pushrod out; turning it counter-clockwise will allow for proper slack reduction. Observe the slack adjuster and pushrod to ensure the adjustment is proceeding correctly.
9. Inspect Other Brake Components While adjusting the brakes, take the opportunity to inspect other critical components like the S-cam, bushing, and slack adjuster for wear or damage.
10. Measure the Stroke Again After making the adjustment, measure the pushrod stroke again. A successful adjustment should result in a stroke of approximately ½ inch. Re-secure the locking device once the adjustment is complete.

Adjusting Self-Adjusting Air Brakes:

Self-adjusting air brakes automatically compensate for brake wear and maintain proper slack. However, if the pushrod stroke exceeds the recommended limits, manual intervention may be necessary. To trigger an automatic adjustment in an emergency, press and release the brakes hard six times, allowing the slack adjuster to reset. If the stroke still exceeds the limit, it’s time to consult a professional mechanic.

Understanding the Air Brake System:

Air brake systems rely on compressed air to activate the brakes, applying pressure to the brake pads and halting the vehicle. These systems are typically found on larger vehicles like buses, trucks, and trailers.

Why Proper Adjustment Is Vital:

Failure to maintain air brakes can lead to brake system failure, resulting in an inability to stop the vehicle. Proper brake adjustment is critical to prevent accidents and ensure your vehicle’s safe operation.

How Often Should Air Brakes Be Adjusted?

As brake components wear over time, the pushrod stroke will increase. It’s essential to check the pushrod stroke before every trip, especially before driving on steep or challenging terrain. Routine maintenance and checks help avoid unexpected failures and keep your vehicle roadworthy. In certain regions, laws may require brake inspections before descending steep slopes.

By keeping your air brakes properly adjusted, you’ll ensure your vehicle’s safety and reliability on the road. Always perform regular checks and adjustments as part of your vehicle maintenance routine.