Because brake linings are designed to wear as they do their job, it makes sense for manufacturers to design linings to last as long as possible to keep maintenance costs down and assure solid braking performance even in abrasive or severe operating conditions.
Source: Silverback HD
The following was published in CCJ's Air Brake Book, 11th edition, sponsored by SilverbackHD. CCJ's Air Brake Book is a complementary industry resource, courtesy of our partnership with SilverbackHD, the Technology and Maintenance Council and Commercial Vehicle Safety Alliance.
Brake manufacturers conduct extensive laboratory testing to establish performance baselines for new linings. “Then we do field testing in addition to that to make sure they perform as intended, and that field testing can be several years,” said Scott Corbett, director of technical service and warranty for Haldex. “Some of the linings have as many as 11 different tests to pass, evaluating factors such as fade, wear characteristics, overall component and material performance and high- temperature performance.”
“… the golden rule of truck parts is that you get what you pay for … In everything there is cheap garbage, there is middle of the road reliable and there is high performance.” – Keith Roth, SilverbackHD Vice President of Operations
Additionally, Corbett said, tests are conducted on peripheral characteristics such as lining squeal and vibration. In all, he noted, it is not unusual for linings to undergo more than five years of extensive testing before being released into the marketplace. “Whether you’re working on a motorcycle or you’re working on a severe-duty off-highway vehicle, the concepts are basically the same,” said John Hawker, a retired consulting engineer that previously worked with Bendix and Dana. “You’re transferring energy and motion – kinetic energy – and converting it to heat. That’s what the friction material in a brake pad or shoe does.”
To understand exactly how a brake lining accomplishes this, think of the process of applying a brake pedal as a controlled burn. “Just like you burn fuel to make the vehicle go, you wear friction material to make the vehicle slow down,” explained Hawker.
Because brake linings are designed to wear as they do their job, it makes sense for manufacturers to design linings to last as long as possible to keep maintenance costs down and assure solid braking performance even in abrasive or severe operating conditions.
Each manufacturer guards the compound list for its proprietary brake lining materials with the same sort of zeal that Coca-Cola and KFC guard the ingredients in their products. “Brake linings are made out of many different materials,” Corbett noted. “You’ll find carbon and fiberglass. And there used to be asbestos until we removed it. But all lining manufacturers have special materials they put in lining, and the higher grade or more expensive the lining is, the more premium materials go into that lining.” Most brake linings consist of different amounts of materials blended together in such a way to maximize heat rejection and component life. These include but are not limited to:
• Fiber materials, usually comprised of steel, carbon, fiberglass, synthetic or ceramics.
• Abrasives such as aluminum oxide, magnesium oxide, zinc oxide and silicon carbide.
• Friction modifiers.
• Fillers, including inorganic, metallic and organic materials.
• Binders, usually phenolic resins and rubber compounds.
• Carbonaceous compounds such as coke, carbon and graphite.
