A primary concern of every fleet professional is the safe operation and stopping ability of the vehicles in his fleet. A truck’s ability to stop, of course, depends on the condition and quality of its braking system, particularly its brakes’ friction material. The friction material used in truck brakes has changed a great deal over the last few decades and continues to change. As an integral part of the braking system, friction material must be chosen to provide the stopping power necessary in a truck’s specific application. This is especially true for commercial vehicles since any given truck model may be put into a wide range of applications. Light-duty vehicles, however, may well benefit from the use of other-than-normal friction material. Consider, for example, police cruisers that may be used in high-speed pursuits with heavy braking demands.
Years ago, asbestos friction material was commonly used in vehicle braking systems – commercial trucks in particular – because of its ability to withstand the high operating temperatures that could be generated in stopping a heavy vehicle. Indeed, temperatures more than 2,000 F created a substantial fire hazard. The health hazards of asbestos, however, have all but eliminated its use in friction materials intended for vehicle applications. Although domestic manufacturers claim that asbestos materials are no longer used in friction products, foreign manufacturers of aftermarket brake parts have no requirement to stop distributing asbestos friction material. OSHA regulates the amount of asbestos dust that is present in vehicle repair facilities, which is where potential problems are found.
Ceramic or non-asbestos organic friction materials were developed to replace asbestos-based products in specific applications. These materials typically exhibit low friction and/or unacceptable wear rates at high temperatures and are very useful in light-duty applications, but are not suitable in many commercial and most heavy-duty operations.
Semi-metallic material was developed, along with ceramic material, to replace asbestos. In comparing the two, Kevin Judge, sales manager of national accounts at Fras-le (http://nabrakes.fras-le.com), a major manufacturer of semi-metallic and ceramic friction material, said, “Semi-metallic material is a bit more aggressive, but can be more noisy than ceramic material. The performance, however, of semi-metallic material makes it a desirable product for use in trucks as well as automobiles used in applications that need high-performance braking performance. It has become the standard for use by the trucking industry.”
More Changes Coming
As a result of environmental concerns, two states have passed legislation that nearly eliminates the use of copper, in addition to several other materials, in friction material. Three years ago, both California and Washington passed laws mandating that friction material used in brakes contain no more than 0.5 percent of copper by weight. While various portions of the laws take effect at different times, they have spurred the industry to develop compliant materials that will deliver satisfactory stopping performance. “As an industry, we are being challenged in going copper-free after 2019,” Judge said.
Not surprisingly, these laws put additional financial burdens on manufacturers and distributors. They may well be enough to cause some suppliers to leave the business, resulting in fewer product choices for fleets.
While fleet managers seek a long service life from brakes, they also know that brake pads and blocks will wear out and need to be replaced. Be sure to do your homework before you go to market. “Fleet managers should be prepared to accurately describe their fleet’s applications when they go to market to purchase replacement brake pads or brake linings,” Judge said. “Terrain is important. The hills of Pittsburgh require different material than the flatlands in Des Moines. They should be aware of the load that they’re carrying. Is it a constant load? Is going to be variable? Is it going to be loaded off and on? Will the application be stop-and-go, or will it be over-the-road? This is the kind of information that brake service technicians need to know before they can make good recommendations regarding friction material.”
If you plan on making a change in friction material of replacement pads or liners, test the material before making a purchase. It’s not unreasonable for a fleet manager to request sample material for his own tests. Judge said that he often gets asked for samples. Tim Bauer, director for undercarriage products at Meritor Aftermarket (www.meritor.com), concurs. “Always test the friction material you’re considering purchasing,” he said. “Look at long-term replacement [cost versus price]. Be wary of container loads of low-price friction. Do they meet safety standards like FMVSS 121? What kind of warranty is offered? Who will back you up in the case of a failure or other problems?”
Bauer also urges that you never replace or service a component on one wheel end only; always do both wheel ends. This is especially true for work on front axles. In addition, if hardware comes packaged with replacement brake pads or linings, use it. “Don’t forget your hardware works just as hard as the linings,” Judge said.
Anytime a technician pulls a wheel, have him measure the thickness of the pad or lining as well as the run-out of the rotor or drum. Have him inspect the hoses to make sure they’re not worn or frayed, and ask him to check all the hardware to ensure it’s in good shape.
Because friction material is just one piece of a very important system comprised of parts designed to work together, when it comes time to replace it due to wear, it should be replaced with material that is as close to original as is possible or with material that you have tested to ensure satisfactory operation in your application.
About the Author: Tom Gelinas is a U.S. Army veteran who spent nearly a decade as a physicist before joining Irving-Cloud Publishing Co. While at Irving-Cloud, he worked in various editorial capacities for several trade publications including Fleet Equipment, Heavy Duty Equipment Maintenance and Transport Technology Today. Gelinas is a founding member of Truck Writers of North America, a professional association, and a contributing writer for Utility Fleet Professional.