An air brake slack adjuster is a crucial component in the air brake system of heavy vehicles, such as trucks and buses. Its primary function is to maintain the correct distance between the brake shoes and the brake drum, ensuring optimal braking performance and safety. The slack adjuster is connected to the brake chamber pushrod and the S-cam shaft. When the brake pedal is applied, air pressure pushes the diaphragm in the brake chamber, moving the pushrod, which in turn rotates the slack adjuster. This rotation turns the S-cam, spreading the brake shoes against the drum to create friction and slow down the vehicle. Over time, brake shoes wear down, increasing the gap between the shoes and the drum. The slack adjuster compensates for this wear by adjusting the length of the pushrod stroke, ensuring that the brakes engage properly with minimal delay. This adjustment can be manual or automatic, depending on the type of slack adjuster. Manual slack adjusters require regular inspection and adjustment by a mechanic to maintain the correct brake clearance. In contrast, automatic slack adjusters self-adjust during normal brake operation, reducing maintenance needs and ensuring consistent brake performance. Proper functioning of the slack adjuster is vital for vehicle safety. If the slack adjuster fails or is improperly adjusted, it can lead to excessive brake lag, reduced braking efficiency, or even brake failure. Regular inspection and maintenance of the slack adjuster are essential to ensure the air brake system operates effectively and safely.

1. **Park and Secure the Vehicle**: Ensure the vehicle is on a flat surface. Engage the parking brake and chock the wheels to prevent movement. 2. **Locate the Slack Adjuster**: Find the slack adjuster on the brake chamber. It connects the push rod to the S-cam. 3. **Check Brake Adjustment**: Measure the push rod travel. It should not exceed the manufacturer's specifications, typically 1 to 2 inches. 4. **Release the Parking Brake**: Release the parking brake to allow the slack adjuster to be adjusted. Ensure the vehicle is secure. 5. **Adjust the Slack Adjuster**: - For manual slack adjusters, use a wrench to turn the adjusting bolt. Turn it clockwise to tighten the brakes until the brake shoes contact the drum. - Then, back off the adjuster by turning it counterclockwise about a quarter to half a turn to ensure the brakes are not dragging. 6. **Check Push Rod Travel Again**: Re-measure the push rod travel. It should be within the specified range. 7. **Test the Brakes**: Re-engage the parking brake and remove the wheel chocks. Test the brakes at low speed to ensure proper function. 8. **Repeat for All Wheels**: Perform the same adjustment process for each wheel with air brakes. 9. **Regular Maintenance**: Regularly check and adjust slack adjusters as part of routine maintenance to ensure optimal brake performance. 10. **Consult Manufacturer’s Manual**: Always refer to the vehicle or component manufacturer’s manual for specific instructions and specifications.

Air brake slack adjusters should be checked during every pre-trip inspection. Regular checks are crucial to ensure the proper functioning of the braking system. Additionally, they should be inspected whenever the vehicle is serviced or if there is any indication of braking issues, such as uneven braking or excessive brake pedal travel. Regular maintenance checks, typically every 10,000 to 15,000 miles, should also include a thorough inspection of the slack adjusters.

Signs of a failing slack adjuster include: 1. **Increased Brake Stroke**: If the brake stroke exceeds the manufacturer's specifications, it indicates that the slack adjuster is not maintaining the correct clearance between the brake drum and the brake lining. 2. **Uneven Brake Wear**: Uneven wear on the brake linings or drums can suggest that the slack adjuster is not functioning properly, leading to inconsistent braking force. 3. **Brake Lag**: A delay in brake response or a spongy brake pedal feel can be a sign that the slack adjuster is not adjusting the brake components correctly. 4. **Frequent Manual Adjustments**: If the slack adjuster requires frequent manual adjustments to maintain proper brake function, it may be failing. 5. **Noisy Brakes**: Unusual noises such as grinding or squealing during braking can indicate that the slack adjuster is not keeping the brakes properly aligned. 6. **Visual Damage**: Physical damage or excessive wear on the slack adjuster itself, such as cracks, corrosion, or bent components, can impair its function. 7. **Inconsistent Brake Performance**: Variability in braking performance, such as pulling to one side or inconsistent stopping distances, can be a sign of slack adjuster issues. 8. **Automatic Slack Adjuster Not Self-Adjusting**: For automatic slack adjusters, if they are not self-adjusting as they should, it indicates a malfunction. 9. **Excessive Pushrod Travel**: If the pushrod travel is beyond the recommended limits, it suggests that the slack adjuster is not effectively maintaining the brake system's clearance. 10. **Brake Warning Lights**: In some vehicles, a brake warning light may illuminate if there is an issue with the brake system, potentially indicating a slack adjuster problem.

No, automatic slack adjusters should not be manually adjusted. Automatic slack adjusters are designed to maintain the correct brake clearance automatically, and manual adjustment can mask underlying issues or damage the adjuster. If the brakes are out of adjustment, it typically indicates a problem with the adjuster or other brake components that need to be inspected and repaired by a qualified technician. Manual adjustment can lead to improper brake function, increased wear, and potential safety hazards. If an automatic slack adjuster is not maintaining the correct adjustment, it should be checked for proper installation, lubrication, and function, and replaced if necessary.