Brakes & friction

Brakes & friction

Buying heavy-duty brakes for optimum stopping distance.

Having met the requirements of the first phase of new stopping distance regulations for commercial vehicles, brake system and friction materials suppliers are now focused on the next set of requirements.

Phase two regulations that will take effect on Aug. 1, 2013 cover loaded stopping distances for two, three and four or more axle vehicles in specified GVWR ranges.

“Over the past few years, we have been working on new formulations and friction materials to satisfy the upcoming requirements,” said Tom LeBlanc, OE sales manager at Fras-le North America Inc. “We have also been developing new materials that address regulations covering copper and heavy metal content.”

The regulations LeBlanc refers to are now in place in California, Washington and Rhode Island, with other states expected to follow suit beginning in 2014. Other aspects of the content rules go into effect in 2015, 2021 and 2025. The goal is to reduce and eliminate particles that enter storm drain systems and ultimately impact fresh water supplies and surrounding habitats.

“Copper was traditionally a popular material in brake linings,” LeBlanc related. “Most of the linings we produce today do not contain copper, so there should not be a change to the formulation, or in stopping distance or lining life. Where copper and other metals were used, these goals are significant but also achievable.”

Fras-le heavy-duty friction materials are exclusively distributed by Meritor for aftermarket use on new and remanufactured brake shoes in North America, a supply partnership that has been in place for 16 years. The company also offers its line of aftermarket disc brake pads directly to warehouse distributors and fleets and is the OEM friction provider on a majority of North American medium-duty work trucks.
Fleet challenges
At the recent TMC annual meeting, TMD Friction identified brake issues that are still proving to be a challenge for fleets. “Many fleets don’t fully understand or track their brake life cycles, especially as they relate to their different types of vehicles, loads and routes,” said Jim Clark, director of engineering for North America. “Fleets also have concerns about new stopping distance rules that require larger drum brakes and higher friction linings, and about old problems that are still around, like brake balance.

“Additionally,” Clark continued, “mechanics don’t always have proper gauges for measuring lining wear, and don’t understand the minimum lining thickness for letting a vehicle return to service. Finally, not all fleets recognize the value of premium linings. If a single brake reline can be eliminated from a vehicle’s brake life cycle, then the small added cost of a premium brake reline kit is easily justified.”

TMD’s presentation also served to introduce its new Textar Fleet Assistance Program, which includes direct communication with TMD engineers to help fleet managers analyze brake life cycles and costs, select the appropriate friction for each application and answer other brake-related questions. Offered in the program are free, custom-made lining wear gauges for both drum and disc brakes for any fleet using Textar products.

Allison retarder: taking the heat off brakes
It’s a simple equation: every time the brake pedal goes down, brake temperature goes up. And it stays up, thanks to modern, wind-cheating vehicle bodies. Their lower stance means less resistance, but it also means less airflow over the brakes, depriving them of their only cooling source. The only sure way to keep brakes cool is to stay off them—and an Allison retarder can help you do that.

Allison Transmission said its integral hydraulic retarder is basically a vaned flywheel in the transmission housing. The transmission directs oil into the retarder housing to absorb the vehicle’s energy through the drive shaft. The absorbed energy is converted to heat and dissipated through the vehicle’s cooling system.

Resistance to the flywheel, augmented by stators on the inside of the housing, delivers braking power to the driving wheels. More oil in the housing means stronger braking. And since there’s no mechanical friction or wear to shock the drivetrain, there’s better control of maintenance costs, too.

Available on Allison 3000 and 4000 Series fully automatic transmissions, Allison’s integral retarder is ABS compatible and can handle virtually the entire braking demand in most situations, the maker said, adding the service brakes are only needed to bring the vehicle to a complete stop or as a safety backup.

Tests conducted at the Transportation Research Center in East Liberty, Ohio, proved the Allison retarder’s effectiveness in a taxing, level stop-and-go duty cycle. Without the retarder, front brake temperature reached 266 degrees F, while the rear linings topped out at 390.2 degrees F. With the retarder applied, brake lining temperatures on the front brakes only reached 120.2 degrees F, and 172.4 degrees F on the rear brake pads—less than half the increase measured without the retarder.
For more information, talk to your truck dealer or contact an authorized Allison distributor.

The Textar Fleet Assistance Program starts when a fleet manager fills out an information sheet that breaks down vehicles into smaller “mini-fleets” that likely have different brake life cycles. Examples of mini-fleets could be tractors versus trailers, or long haul sleeper tractors versus short haul day cabs, or flatbed trailers versus van trailers. TMD engineers use the fleet’s information, Clark explained, to calculate if life improvement from its linings would push relines out for the life cycles of each mini-fleet, and how many total relines would be saved. These calculations are based on wear testing of aftermarket linings on specialized dynamometers.

“If a fleet will try Textar products as part of the program, TMD will supply free lining wear gauges that have been customized to the fleet’s brake life cycles,” Clark added. “With these gauges, fleets can avoid wasting linings as a result of a lining being removed prematurely because the mechanic is not sure it will make it to the next inspection.”

TMD Friction also introduced a new friction material for heavy-duty air disc brakes. The new material is designated Textar T3080 and is engineered for applications where high torque levels are required to meet FMVSS121 Stopping Distance Regulations. In addition, Textar T3080 already meets the 2014 and 2021 “Better Brakes Rules” environmental regulations for heavy metals and copper content.

Precise measuring
“The friction materials are certainly important, but the manufacturing process is also a very key factor,” said Mac Deal, brake products segment leader for Stemco LP. “The friction production process begins with a thorough and precise measuring of raw materials to exact proportions by formula. The raw materials are then mixed and diffused in industrial hoppers, weighed precisely into long metal trays, and formed into long slabs. It is at this time that friction is transformed into brake lining by way of a number of manufacturing processes.”

To manufacturer friction materials, Stemco employs a patented “Wave Process” that begins with the cold mold cycle, which creates the unique wave pattern. Hot molding then forces the waves to condense under heat and pressure. Aligning the friction density into column structures ensures less heat susceptibility, which results in quieter, longer lasting brakes, Deal added.haldex

Another friction manufacturer that offers a range of products for fleets is Abex, a Federal-Mogul brand, which supplies heavy-duty commercial-grade brake products, including pads, linings and shoes. Abex also packages multiple products in kits containing all the parts needed for specific brake repairs, and according to the company, ensures that all replacement parts replicate the original equipment in terms of quality, fit and form.

Another friction maker, Haldex, offers comprehensive product support through a nationwide network of brake shoe relining facilities. Relined with the company’s GreyRock brake lining formulations, the shoes undergo over 30 quality checkpoints and inspections for table, web, anchor and roller end, shoe stretch and collapse wear and damage. Checked as well are rivet holes, coating coverage and lining fit and rivet torque. The company said it also offers technical assistance, as well as installation and maintenance training.


Universally, brake friction material manufacturers agree that fleets can avoid reduced stopping power by replacing brake linings with those specified by the OEM. Committing to a like-for-like replacement is the only way fleets can maintain the same high level of safety NHTSA intended by mandating improvements in stopping performance, noted a technical report from Bendix Spicer Foundation Brake LLC (BSFB), and it’s a certain way to maintain compliance with new federal standards designed to improve highway safety.Stemco wave process

However, the report continued, many fleets remain unaware that the routine maintenance decision for specifying replacement friction can negate the technological advancements of the brakes, and potentially compromise safety. “Relining today’s high-performance drum brakes with typical aftermarket friction, and not the linings specified by the OEM,” it stated, “can significantly reduce a vehicle’s braking capability and lead to longer stopping distances.”

In its recommended practices, Bendix also noted, the Technology and Maintenance Council (TMC) of the American Trucking Associations agrees, “It is essential that the replacement brake linings function as well as the material originally supplied on the vehicle.”

Engineering teams from brake and friction materials manufacturers, in concert with vehicle OEMs, continue to invest in designing and specifying brake packages for longevity and safety.

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