Cummins explains why it's important to inspect the entire foundation braking system during service.
Brake system issues are a leading cause of out-of-service violations. When performing brake maintenance, it is important to inspect and maintain the entire braking system to prevent these violations. The goal is not to have more brake jobs, but rather for brake jobs to be more complete, resulting in more uptime. Automatic slack adjusters, brake shoe lining, brake drum, camshaft and the brake chamber bracket are the top five braking components responsible for the most out-of-service citations.
Proper brake maintenance can prevent costly roadside repairs, reduce downtime, and decrease the number of fines and enforcement penalties. Here’s a complete look at what goes into proper brake maintenance.
To maintain proper brake adjustment and provide balanced braking, automatic slack adjusters (ASA) must be inspected to confirm an identical ASA is used on both sides of an axle and the adjuster mechanism is functioning properly. Measure and confirm “free-stroke” is correct. If found to be incorrect, determine the root cause and correct it; do not just adjust the brake.
Check lining thickness and look for cracked linings as well as ones covered with oil, grease or fluid from a failed camshaft seal/bushing or wheel seal. Rust jacking occurs when harsh chemicals, such as ones used for deicing, get between the table of the shoe and the lining. The shoe coating fails, then rust forms and the lining cracks and is lifted off the table resulting in premature failure of the lined shoe.
Start the brake drum inspection by measuring drum wear. The diameter of the drum should not be beyond the manufacturer’s limits. As the brake surface wears the drum mass is reduced, resulting in the brake’s inability to dissipate heat. The retained heat reduces friction material life and braking performance.
Also, check to see that no part of the drum is missing. Look for scored or heat-checked drums. Upon visual inspection, a heat-checked (cracked) brake drum will appear closed at room temperature. Heat checks open and close with each brake application. Be aware that heat checks may not necessarily be at the edge of the drum. In addition, if you find hot spotting or scoring, replace the brake drum.
When inspecting the camshaft look for missing or broken components such as cam rollers, springs, anchor pins and mounting bolts. Check cam bushings, cam tubes, and retaining rings. Be on the lookout for excessive wear of the camshaft head and rollers, as these can cause brake stroke fluctuations and result in exceeding the maximum range of the camshaft. Also check to see that the camshaft and camshaft tubes are properly lubricated.
Check camshaft radial movement by moving the camshaft head in all directions, and use a dial indicator to measure movement. Next, move the camshaft axially.
The service chambers and spring brakes on each end of an axle must be the same size. Inspect to make sure push rod stroke is not greater than the industry limits. There should be no damage to the service chamber, spring brake or push rods/clevis. Service chamber or spring brakes should be fastened securely.
There are long stroke and standard stroke chambers, and it is important to know which you are working with. The Society of Automotive Engineers recommends using two of three options for identification. Long stroke chambers have a trapezoidal shaped tag, square port boss and permanent identification on the brake chamber.
To test the return spring, force the pushrod back when the brake is released. Release the air from the service chamber. Release the spring brake and pull the pushrod out. When you let go, the pushrod should return to a full released position on its own. Symptoms of a bad return spring include an under-adjusted ASA, uneven release, rod not returning to full release position, and dragging brakes. Source