Did you know that according to the Federal Motor Carrier Safety Regulations, Section 396.25, you must be qualified to inspect and work on air brakes?

But even if you aren't qualified, that doesn't mean you shouldn't check your brakes regularly and bring any problems to the attention of a qualified mechanic. This is because despite the required use of automatic slack adjusters (ASAs), brake problems are still the leading reason that highway inspectors put trucks out of service. With so much riding on your brakes, you shouldn't leave them to chance.

Where They Wear Out

It's no surprise that brakes and brake parts wear out. Your brakes use friction to convert your vehicle's kinetic energy, or energy of motion, into heat energy. The conversion is what slows or stops the rig. But it also produces extremely high temperatures and the friction causes lining wear.

Slack adjustment compensates for some, but not all of the wear. Brake shoe linings wear away, so the actuating mechanisms must be adjusted, manually or automatically, to take up the slack created by the wear. Manual adjusters should, by law, be set by a certified brake technician. Automatic adjusters will work well, but only if they have been well maintained.

Linings wear down and must be replaced periodically. Depending on driving conditions and driver technique, they could last from 50,000 to 500,000 miles or more. Pivot holes and other contact points in brake shoes could wear and enlarge during the thousands of applications during this period. When replacing brake linings, it's a good idea to replace the shoes, too.

Danger in Drums

Check brake drums regularly. The friction surface could become glazed or cracked due to uneven or rapid heating. Glazing affects friction. Once cracks grow together, they could cause the drum to shatter, causing brake parts to be thrown from your truck.

Air Brakes

As for air brakes, they are required to have visual indicators to determine if their stroke is within adjustment limits. Some pushrods are marked where they emerge from the brake chamber, but as dirt and grime accumulate, they become difficult to read. Add-on indicators range from electronic devices with remote read-outs to simple clamp-on devices that show stroke at a glance. When you have them, you won't need to measure to determine if you're nearing the limit.

What To Do

Follow this checklist for brake maintenance

• Check slack adjustment regularly, even with Automatic Slack Adjusters (ASAs).
• Make sure slack adjusters operate properly.
• Lubricate slack adjusters at every oil change (more often if you extend your oil drains).
• Check lining thickness at every oil drain. If linings need replacing, do a complete axle, not just one brake. Since friction characteristics vary between linings, this will keep side-to-side stopping forces evenly balanced.
• Check drums daily. Use a flashlight. Look for cracks and discoloration. Both are signs of heat stress. If necessary, replace the drums, again replacing pairs.
• When you get new linings, check to see if you need new drums. Take measurements. Visual inspection is not good enough.