Heavy-duty brake systems

BUSRide Maintenance gathered experts from some of the industry’s leading brake system and component manufacturers to discuss the advantages inherent to different brake systems; operating vs. acquisition costs; preventative maintenance; and extending brake life.


The panelists for this discussion are:

Brad Begleyvice president of salesWebb Wheel

John Wolfsenior sales manager, specialty productsMeritor

Keith McComsey director of marketing and customer solutionsBendix Spicer Foundation Brake

Mark Goedtelproduct manager, brakesAxleTech International


What considerations should an operator make when specifying brake systems – and in choosing between disc or drum brakes?

Brad Begley: This decision can boil down to several factors including the overall weight variations between braking systems specifically for weight sensitive applications, system component costs both in first-fit and replacement parts, the aftermarket availability of the replacement parts, and the duty cycle of the specific vehicle’s application to name a few.

Mark Goedtel: For the coach and bus segment of the heavy-duty vehicle market, we think it is clear over the past five to ten years that Air Disc Brake Systems are superior to Drum Brake Systems. Typically, Air Disc Brake Systems require less maintenance, are easier to service, and provide extended service intervals. Additionally, Air Disc Brake Systems provide more consistent brake power and improved safety.

When considering what system to specify, bus operators need to carefully evaluate expected vehicle duty cycle to then match caliper design and type, and related components to the level of performance generally expected from the brake system. A more robust caliper should be used if expected duty cycle is in the more severe range.

Keith McComsey: They should consider a few important factors, such as if they trying to improve their safety “footprint” and/or if they want to look more closely at their total cost of ownership (TCO). 

Currently, drum brakes are mostly used on bus chassis. However, considering air disc brakes at all wheel positions offers a number of benefits. Air disc brakes provide an incremental level of improvement in both safety and TCO. They offer shorter stopping distances and better brake balance between the left and right side at the steer axle, producing straighter, more stable stops, and giving the driver a more car-like feel.  During repeated hard braking events, drum brakes are more susceptible to brake fade, which is a condition that occurs when the drum has heated up to the point where it is expanding away from the friction – thereby making less friction contact, resulting in longer stops. With ADB, brake fade is virtually eliminated.

Also, during hard braking events, there is a load shift to the front axle, which requires the front brake to work harder, and therefore the friction tends to wear at a faster rate. By having ADB on the front axle, it extends the life of the friction over drum brakes, making the front steer brake with ADB a good opportunity. The operator would maximize the life of the brake friction at every wheel position. Since ADB brake pads take the amount of time to replace, the operator would see much lower overall maintenance costs. So, there are numerous benefits to the operator with air disc brakes.

John Wolf: When fleets are specifying their brake system requirements, the biggest consideration should be the vehicle’s duty cycle. Many factors are at play here: number of stops per mile; size and type of the vehicle, including length, type of drive system (diesel versus hybrid versus CNG versus electric); and weight, both loaded and unloaded. Also, one needs to consider whether the vehicle is equipped with a hydraulic retarder. If the answers that the fleet provides to these questions tend to be on the higher side, then their application would be considered high-energy application, and disc brakes should be strongly considered. Disc brakes:

•Manage the higher energy (temperature) more effectively

•Rotor life is typically two to three pad changes, resulting in less down time 

• Exhibit more consistent brake balance side to side

•Offer better operator comfort as they are typically quieter and exhibit less pull and shimmy than drum brakes

How important is it to consider brake operating costs – in addition to acquisition costs – when evaluating green initiatives?

Goedtel: Some brake component parts, like friction material, now have higher acquisition costs due to new hazardous material regulations. Other components, such as remanufactured calipers, have greatly reduced acquisition costs with no change in operating costs, and certainly reduce resource demands.

Begley: Transit property maintenance managers have wrestled with the question of cost per mile versus lowest acquisition price seemingly forever. Often times, premium, longer-life components can come with a higher price tag. For properties that can properly document performance testing results, a higher up-front cost can often result in lower total operating costs. This is the case with Webb’s Vortex brake drums. With their patented heat-dissipating design, these drums can extend both brake drum and brake shoe life, resulting in less waste over the life of the bus. Similarly, Webb’s ADB rotors with LifeShield™ technology can prolong rotor life by fighting corrosion and providing greater wear resistance.

McComsey: It’s always important to consider both initial acquisition costs and operating costs when looking at various brake opportunities. So when it comes to green initiatives, it can be looked at in a couple different ways.

In January of 2015, the EPA, various U.S. states, and automotive industry representatives signed an agreement to reduce the use of copper and other materials in motor vehicle brake pads to certain levels by 2021, and a further reduced level by 2025. The initiative will decrease runoff of these materials from roads into the nation’s streams, rivers, and lakes to help protect the environment. Currently, the California and Washington laws effectively help drive the industry, leading brake friction material manufacturers to change all of their U.S. product lines to be compliant with those laws. The changes will ultimately benefit the entire nation’s watersheds and waterways, not just those in California and Washington. Bendix is voluntarily complying with this initiative for all new ADB pads released. The operating cost consideration will be tied to penalties in states that will enforce the initiative. 

Bendix also supports green initiatives by offering remanufactured brake shoes for the aftermarket.

Remanufacturing always involves either replacing or repairing a core’s components to return it to its OEM specifications, which includes replacing “wear” components such as brake friction. Generally, a remanufactured component will cost less than a service new component.

How important is it to maintain brake systems with OEM parts and components, as opposed to parts from aftermarket suppliers?

McComsey: When it comes to safety equipment such as brakes, it is very important to utilize genuine Original Equipment Manufacturer (OEM) parts for replacements during maintenance. When the vehicle was designed, tested, and manufactured, it was all done with components that are designed to work as a system to achieve a certain level of performance. For example, one measure of a vehicle’s brake system performance in FMVSS-121 is stopping distance. Depending on the vehicle configuration, OEM components were designed to exceed the requirement (shorter stopping distance). So the best way to maintain that OEM level of brake performance is to utilize the OEM brake components that were used at the time of manufacture. Lower cost (non-OEM) brake components may not meet performance requirements such as the original stopping distance, and in some cases, add nearly 100 feet to stopping distance. As a driver, can you imagine that one day, your vehicle stopped in 225 feet, and the next day after a friction change to a lower cost friction, your vehicle stopped at 320 feet? Just by changing to a lower cost friction, you lost roughly 5-6 car lengths in stopping distance. 

And when it comes to cost, non-genuine parts might initially cost less, but in the long run, when you look at your vehicle’s total cost of ownership, it will end up costing more.  Lower cost friction may wear at a faster rate, shortening the service interval and requiring more frequent replacements. It may also run hotter, causing damage and/or shortening the life of a brake drum or air disc brake rotor. 

Wolf: It’s extremely important to maintain the brake systems with OEM parts. To meet regulatory stopping requirements, Meritor designs and supplies disc and drum brakes based on parameters provided by vehicle manufacturers. Included in Meritor’s design and validation process is the consideration of energy (heat) and ability of the brakes to dynamically manage torque. If any changes are made, such as using non-OE aftermarket parts, there is risk of upsetting the balanced brake system. For example, changing one axle set of pads to a different friction formula runs the risk of overheating the other axle and thus the vehicle not meeting the federal mandates for stopping distance.

Goedtel: There is much confusion over what “OEM PARTS” really means in today’s marketplace. Vehicle OEM’s do not manufacture Brake Parts or Brake Systems, they purchase and install them from other manufacturers to meet certain operational specifications. Many of these tier one and tier two manufacturers also produce aftermarket products that are the similar products as supplied to OEM’s but are usually marketed under a different brand name. Reputable tier two manufacturers usually produce multiple brands of component products that meet a range of performance specifications: from high-end specifications and OE specifications to lesser demanding specifications for some more competitive market situations.

AxleTech is both an OE brake manufacturer and aftermarket supplier. We supply only OEM-grade or high-end grade products and components in our brake product line. We have a dedicated brake engineering team that focuses on developing complete brake offering across all our targeted markets, including brakes used on military vehicles.

Our brake product line undergoes extensive benchmark part testing against the very best global products. This allows us to supply high quality aftermarket brakes to all market segments.

Fleet operators can maintain brake systems with either OE or aftermarket brake components from reputable manufacturers.

Can driver behaviors be modified to extend brake life? If so, in what ways?

Goedtel: AxleTech believes driver behavior can be modified to extend brake life and improve brake-related safety issues. Information from proper monitoring systems like the AxleTech/Circuitlink system monitor, indicate “hard braking” and “actual acceleration events,” along with route details. This information can be used to educate drivers on better braking techniques, leading to improved safety and extended braking system life.

Begley: Drivers can play a significant role in the life of a vehicle’s braking system. Ultimately, no one has a better feel for the day-to-day performance of a particular bus than the driver. Being on the front line, the driver plays an important role in communicating with maintenance personnel regarding any potential issues. Additionally, a driver’s braking practices have a direct impact on the amount of heat that builds up in a wheel-end. Excessive wheel-end heat can cause brake fade, premature friction material wear as well as damage to tires which can lead to failure of tires at wheel beads. Webb Vortex® drums are uniquely designed to better dissipate that heat and reduce the dangers of brake fade and tire damage.

McComsey: There are a number of ways to maximize brake life. Driver behavior certainly has a direct effect on a brake life. If a driver repeatedly makes hard stops due to aggressive driving habits, it will have a negative impact on the brake components and performance. Aggressive behavior and frequent hard stops can heat up a drum brake, creating a brake fade condition, and increasing stopping distance. On an air disc brake, excessive heat can increase the likelihood of stress cracks occurring in the brake rotor. Heat also accelerates the wear rate of brake friction on any brake.

Wolf: Yes. Driver training will influence brake life. Through continuous training, drivers will better understand the importance of monitoring for symptoms of brake-related issues (warning lights, brake pull, performance degradation, vibrations when applying the brake, unusual noises, etc.). Recognizing and reporting these conditions back to the maintenance manager will extend the life of the vehicle’s brakes overall and potentially prevent catastrophic failures.

In what additional ways is brake technology affecting green initiatives?

Goedtel: AxleTech recently launched a remanufactured brake caliper line, which will help reduce resource demands. We have also converted our friction formulas, which are produced to our specifications designed to meet new hazardous material regulations and provide superior performance.

AxleTech is also developing a complete line of Electric Drivetrain Systems for electric vehicles, including electric buses. We have partnered with Wrightspeed to provide a custom axle for their Geared Traction Drive™ (GTD) technology. The drive unit, fitted on trolleybuses in Wellington, New Zealand, features high power regenerative braking. The complete powertrain package includes a patented range extending turbine generator, and cuts emissions and fuel consumption without sacrificing power or range.

Wolf: Brake friction material will be affected in the future, as brake lining manufacturers, including Meritor, move toward lining formulas designed to reduce copper, asbestos and some other elements used in pads. Different names are used to describe the regulations that are in effect, such as “better brake rule” or “copper legislation.” These laws that were initiated in California and Washington require that brake linings must contain less than five percent after 2021 and less that 0.5 percent by 2025.   Since copper is used today to manage energy and help with friction mu characteristics, alternative materials are being tested as replacement formulas are developed.  Although the laws mandating the reduced consumption of copper presents challenges to the lining manufacturers today, the overall benefit to the environment is the ultimate goal.

McComsey: With air disc brakes offering longer service intervals, there are fewer parts being replaced less often. This ultimately saves money and resources. Also, as wear sensing opportunities come into play, operators and fleets can optimize their brake maintenance schedules by getting the most out of their brake friction. For example, an operator would be able to determine when a brake requires replacement during operation, rather than only during scheduled inspections. In some cases, good friction is being thrown away, because the vehicle is in for inspection, and the operator isn’t predicting friction life to optimize when to schedule maintenance.

How has onboard, real-time monitoring affected preventative maintenance on disc brakes? On drum brakes?

Begley: The introduction of onboard, real-time monitoring allows fleet personnel the opportunity to make adjustments and/or small repairs to avoid catastrophic wheel-end failures or damage to components.

Monitoring of air disc brake wheel ends can allow for an in-service warning of premature disc pad friction wear as well as real-time alerts to wheel end heat spikes which could indicate caliper or hardware related failures. Such failures could result in premature wear or damage to disc brake rotors and calipers. Webb’s LifeShield™ Rotors are treated to withstand intense heat spikes at a level higher than standard rotors and can extend the interval of a bus reaching a point for preventive maintenance once the heat event is detected.

Drum brake wheel-end monitoring allows for sensing of heat spikes which could be related to hardware failure or premature friction wear. Heat warnings can alert a driver to slow down or to seek preventive maintenance to avoid damage to drums, wheels, tires and related equipment. Webb Vortex® drums help better dissipate heat in extreme braking conditions and lessen the long-term effects of heat spikes on brake linings and tires.

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