Spec'ing and Maintaining Brake Systems for Utility Vehicles

A day in the life of a utility vehicle involves more than getting from point A to point B. From terrain challenges to load bearing requirements, the utility industry presents a variety of work situations and demands that make it almost impossible to spec a one-size-fits-all vehicle solution.

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By Gary Ganaway

A day in the life of a utility vehicle involves more than getting from point A to point B. From terrain challenges to load bearing requirements, the utility industry presents a variety of work situations and demands that make it almost impossible to spec a one-size-fits-all vehicle solution.

This level of specialization and challenging working conditions make it even more important to ensure utility fleets and drivers are equipping their vehicles with the proper brakes for the job, as well as practicing correct maintenance. Safety, performance and return on investment (ROI) depend on proper spec'ing and maintenance.

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Vehicle Application is Key to Spec'ing the Right Brakes

At Bendix, engineer teams work full time with original equipment manufacturers (OEMs) to specify brakes for all commercial vehicle applications, including the utility industry's diverse needs. The company encourages all utility fleets to consult the application engineers employed by their vehicle manufacturers and brake suppliers to discuss the correct equipment to deliver the performance, reliability and durability needed from their brake systems.

If a utility vehicle is likely to travel unpaved roads or construction sites, for instance, it may necessitate a more durable brake with extra support in the form of external brackets or gussets, designed to handle rougher usage and minimize breakage from vibration. Dust shields may also be recommended to prolong brake life by keeping foreign material out of the brake mechanism.

Conversely, spec'ing the brake system on a utility vehicle designed for an urban environment is likely to focus more on keeping the brakes cool during repeated stops. Reducing brake fade, improving wear and minimizing noise are also key points to consider.

Load, wheelbase, center of gravity, maximum speed and tire size must all be taken into account for engineers to properly size the brakes, chambers and air system for a particular utility vehicle. Utility fleet managers also face the choice of air disc vs. drum brakes, which have evolved in recent years.

Larger and more powerful drum brakes have been engineered in response to the recent federal reduced stopping distance (RSD) mandate for Class 8 tractors. These high-performance brakes deliver the increased torque and reduced fade necessary for shorter shops. These new drum brakes can sustain that torque throughout the stop, reducing stopping distances.

Air disc brakes are growing in popularity because of the advantages in stopping power and brake life. Faster pad replacement, which simplifies service and improves uptime, is one more reason why fleets and other end-users are increasingly choosing air disc brakes.

Brake Inspection and Maintenance are Critical

Proper maintenance using the right replacement parts help keep air disc and drum brakes trouble-free. At Bendix, two levels of maintenance are recommended.

First, pre-trip inspections are the primary level of maintenance. These inspections are essential. Drivers should walk around the vehicle and look for obvious problems such as loose hoses and leaks, and check disc brake rotors for cracks. If dust shields are not installed, it is recommended the driver check the brake's lining wear; this can be done without removing the wheel. It is not necessary to get under the vehicle before every trip, but once or twice a week is recommended.

Second are preventive maintenance inspections, usually based on set mileage intervals. For drum brakes, this inspection includes checking for lining wear, excessive lining cracks and inspecting automatic slack adjusters. Bendix recommends following the manufacturer's instructions for slack adjuster installation and maintenance because setup procedures will vary based on each manufacturer's recommended procedure.

Air disc brakes require no maintenance on their automatic adjusters, which are built in, sealed and lubed for life. Air disc brake pads should be checked for wear and replaced if necessary. Pad replacement should take some 15 minutes per wheel-end once the wheel is removed. Brake rotors should be checked for cracks, although these are rare, and all rubber boots and seals should be visually inspected to ensure they are intact.

Another concern is replacement of spring brakes, which are used for parking air braked vehicles. Not all aftermarket spring brakes are required to meet the Society of Automotive Engineers (SAE) standards for parking output. Vehicles fitted with inadequate spring brakes are at risk of rolling away while the vehicle is in park.

During operation, be aware of brake system problems such as smoke, which could be a sign of a wheel lockup or a dragging brake, or brake pull—the feeling the vehicle is being pulled to one side while braking. Brake pull can signal an issue with a lining or a slack adjuster. In either case, a technician should inspect the braking system.

Choosing Original Equipment Manufacturer Replacement Friction is Step One

As noted, new high-performance drum brakes and latest-generation air disc brakes reduce stopping distances and perform better and with less fade than their predecessors. Many fleets and drivers, however, remain unaware a routine maintenance decision can negate those technological advancements. Relining original drum brakes with low-cost, underperforming aftermarket friction rather than OEM specified linings can significantly reduce a vehicle's stopping capability.

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Using OEM replacement friction is vital to maintaining the effectiveness of high-performance drum brakes. OEM replacement linings designed to keep braking systems in compliance with RSD legislation perform significantly better than pre-RSD friction, especially at higher speeds. And, when subjected to temperature increases during brake usage, OEM linings also maintain their performance levels more effectively.

The American Trucking Associations' Technology and Maintenance Council (TMC) has noted in its recommended practices that selecting the correct replacement brake is an important component in the overall safety of the vehicle. TMC Recommended Practice 628B stresses: "It is essential that the replacement brake linings function as well as the material originally supplied on the vehicle."

Federal Motor Vehicle Safety Standard (FMVSS) 121 has dynamometer and vehicle test performance requirements. It is essential that the brake system and friction pairing meet both of these criteria. There is some confusion about this because many aftermarket materials are able to pass the dynamometer requirements but not the original equipment vehicle test requirements. Results of this laboratory dynamometer test often are viewed as an indicator that a brake lining will supply the torque output needed to stop a vehicle within the new RSD standards, but this is not necessarily true. The Technology and Maintenance Council has noted in its aftermarket brake lining classification report: "Brakes relined with certain aftermarket materials can have reduced braking output, cause a shift of work to brakes on other axles, and reduce the overall stopping capability of the vehicle."

Bendix engineers compared the performance of an RSD-compliant vehicle with OEM brakes and linings to a popular aftermarket material that passed the FMVSS 121 dyno test but was not suitable for RSD compliance. Using computer simulation software and with nothing else changed, the vehicle's stopping distance showed an increase from 215 feet using the OEM friction to 311 feet with the aftermarket replacement friction—a 45 percent decrease in performance. That 96-foot stopping distance differential is a stark illustration of the safety at stake.

In the utility industry, where vehicles face different duty cycles, work environments and demanding schedules, it's difficult to overstate the importance of carefully spec'ing, maintaining and choosing replacement parts for braking systems. Communicating closely with brake providers and engineers, and following recommended maintenance practices are the keys to keeping a utility fleet running safely and efficiently.

By taking these steps, fleets will sacrifice neither performance nor safety, while strengthening the bottom line.


About the author: Gary Ganaway is director of marketing and global customer solutions for Bendix Spicer Foundation Brake LLC.


About Bendix Spicer Foundation Brake LLC: Bendix Spicer Foundation Brake LLC combines and expands the complementary wheel-end foundation brake technologies of two companies—Bendix Commercial Vehicle Systems LLC and Dana Commercial Vehicle Products LLC. The joint venture, formed in July 2004, is a single, complete source for OEM brake system design, manufacturing, hardware and support for all foundation brake components and actuation systems, as well as all-makes coverage of some 50,000 medium-duty and heavy-duty aftermarket parts. For more information, please visit www.foundationbrakes.com.

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