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Understanding the Facts behind Common Wheel-End Service Misconceptions Can Help Fleets Optimize Braking Systems, Avoid Violations, and Improve Uptime.
In servicing commercial vehicle wheel-ends, fleets and operators sometimes rely on industry practices that are accepted, trusted – and may no longer be valid.
Following is an edited version of the Bendix Tech Tips: Don’t Fall for Brake Maintenance Myths, from Bendix Commercial Vehicle Systems LLC and Bendix Spicer Foundation Brake LLC (BSFB), which addresses common misconceptions, offering the facts behind each to help industry professionals make sound decisions for wheel-end maintenance. The complete version can be found at www.bendix.com.
“Long-held maintenance practices aren’t always best practices. Some are myths – around inspections, adjustments, and spec’ing replacement parts – and following them can cause problems in a vehicle’s most critical safety system,” said Keith McComsey, BSFB Director of Marketing and Customer Solutions. “During this year’s Commercial Vehicle Safety Alliance’s (CVSA) International Roadcheck, nearly 25 percent of the vehicles inspected were placed out of service, and more than four out of 10 of those vehicles placed out of service were attributed to brake-related violations. That number can be reduced by recognizing and rethinking misconceptions around wheel-end maintenance.”
Bendix outlines five of the most common misconceptions.
MYTH: Air Disc Brakes Need to Be Inspected Only Once Yearly
Fact: Air disc brakes (ADB) should be inspected at every preventive maintenance (PM) inspection.
“Among their benefits, air disc brakes have extended service intervals for friction or rotor replacement when compared to drum brakes, but this does not mean that ADB maintenance intervals get extended too,” McComsey said. “Inspecting at every preventive maintenance inspection is still required to make sure everything is in good working order – it’s this regular activity that contributes to the brake’s longevity. Most of these PM inspections do not even require removal of the wheel, making it a quick, easy process.”
MYTH: Adjust Slacks at Every Inspection
Fact: For fleets and drivers operating vehicles equipped with automatic slack adjusters (ASAs), do not manually adjust the ASA if the brake is beyond the stroke limit.
Some technicians servicing drum brakes will adjust ASAs at every PM inspection. Properly installed, operating, and lubricated automatic slack adjusters should never need adjusting after the initial setup – aside from during brake relining. Therefore, Bendix emphasizes that an out-of-adjustment ASA should never simply be manually adjusted to bring it back into adjustment.
MYTH: More Aggressive Drum Brake Friction Will Last Longer
Fact: It’s possible that drum brake friction meant for a higher gross axle weight rating than your vehicle’s may last longer, but it will also likely cause more drum wear and shorter drum life. And because it may provide more torque output, it could lead to problems with brake imbalance.
Bendix advises spec’ing drum brake friction in line with your gross axle weight rating. There may be instances when a different friction is called for, but normally you should use the same rating as the axle.
MYTH: Unless You Hear a Leak, There’s No Need to Inspect Brake Chambers
Fact: You should inspect your brake chambers at every PM inspection. Making sure your chambers are working properly is essential to the safe operation of your braking system. Frequent and more thorough inspections are required.
In addition to listening for air leaks around the chamber, check for missing parts such as dust plugs, clevis, and clevis pins; look for obvious damage to the chamber, such as dents, corrosion, and bent pushrods; and check to make sure the chamber mounting is not loose.
MYTH: All Brake Shoes Today Meet RSD Requirements
Fact: Not all brake shoes meet federal Reduced Stopping Distance (RSD) regulations.
The aftermarket provides many friction options for both air disc and drums. Not all replacement friction marketed as acceptable, however, will meet FMVSS-121 requirements defined at the time of a vehicle’s manufacture. This could therefore impact performance, including stopping distance and parking capability.
When relining brakes on vehicles affected by federal stopping distance regulations, ask suppliers for evidence of compliance.
However, the best way to maintain FMVSS-121 compliance is to maintain the original OEM performance to which it was tested. To maintain OEM performance, Bendix recommends that fleets and owner-operators replace friction with like-for-like components to maintain the original manufacturer’s braking performance levels – contributing to safer roads and reducing the risk of liability. Fleets may put themselves at risk if they choose a lower performing aftermarket friction that negatively impacts a vehicle’s braking performance or stopping distance.
“Don’t leave anything to chance when it comes to replacement friction,” McComsey said. “An improper choice can result in reduced braking performance – in some cases, adding multiple car lengths to a stop – reducing safety and putting your drivers and the fleet at risk.”
The complete Bendix Tech Tips series can be found in the Bendix multimedia center at knowledge-dock.com. Further instructional videos and interactive training on foundation drum brakes and friction are available at the Bendix On-Line Brake School, www.brake-school.com.
For more information on wheel-end and air dryer maintenance, contact the Bendix Tech Team at 800.AIR.BRAKE and download Bendix Tech Tips at www.bendix.com.

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