Putting The Brakes On

We're putting tougher demands on truck brakes today than ever before, but when it comes to replacement brake linings, it's all too easy to compromise the performance that was carefully engineered into the truck in the first place.

"We have more aerodynamic tractors," explains John Hawker, service engineer, Bendix Spicer Foundation Brake. "The truck slips through the air easier today and faster today than it did even two years ago." A move toward more synthetic lubricants also reduces drag. "So we have a vehicle that is very fuel-efficient, but when you take your foot off the throttle, you get very little deceleration from the natural drag of the vehicle. So the only way it slows down is by applying the brakes."

To meet Federal Motor Vehicle Safety Standard regulations, as well as fleet performance and life expectations, original equipment manufacturers produce a wide variety of friction materials for brake linings, specifically designed for each axle weight rating, vocation, duty cycle, and brake operating temperature.

Each friction material has its own "secret recipe," explains Joe Kay, engineering manager, brake product line for ArvinMeritor. "As a result, you get friction materials that have their own personality. They'll react differently at different temperatures or speeds."

Some friction materials, for instance, are good at standing up to the start-and-stop life of a garbage truck, while others are good at holding vehicles on hills when parked – important for a fire truck.

Replace with the wrong type of brake linings, and the relined brakes can have reduced braking output, causing brake imbalance – a shift of work to brakes on other axles. This not only reduces the overall stopping capability of the vehicle, but also can lead to shorter lining life, and overheated and even cracked drums as those brakes are overworked.

Unfortunately, picking the right brake lining is easier said than done.

Performance of new equipment is regulated by the National Highway Traffic Safety Administration, which even now is in the midst of toughening tractor brake standards by requiring shorter stopping distances. But the Federal Motor Carrier Safety Administration, which regulates in-service equipment, has no regulations in place that require replacement brake materials to meet the same standards.

"Once the vehicle's out in the field, after it goes through its lining life, there's really nothing regulating the performance the vehicle has to abide by," Kay says.

As a result, there's an almost bewildering array of options, says Randy Petresh, vice president of technical services for Haldex. "The simple answer is for everybody to reline and replace with the same thing they took off," bought new from the original manufacturer that made the brake for the truck maker.

In the real world, however, that rarely happens. "You've got a lot of suppliers that don't manufacture and sell OEM-approved materials, they're strictly playing the aftermarket business. And all the original equipment manufacturers also have aftermarket friction as well," Petresh says. "So the truck owner or fleet, he's got a lot of choices, a lot of options."

A truck owner may buy on price, because he's got a buddy who sells brake linings, or any number of reasons, Petresh says. "They can select anything – they have no guidelines, no regulations, no specifications that dictate or specify or instruct the users how to select replacement materials."

Breaking The Code

The problem begins with the challenge of knowing exactly what you're taking off the truck in the first place. You can't replace like with like unless you know what it is you're replacing. Unlike tires, which are clearly marked with a standard coding system, you can't tell much from a worn brake lining about what you need to buy to replace it, other than the size.

The existing "friction identification" codes, such as EE, FF, EF, GH, are not considered accurate in determining performance on a full-size brake. These letters are a result of testing small lining samples to SAE J661a. "It's basically a manufacturing quality control check that means nothing in the application of the friction material," Hawker says.

For decades, the friction materials industry, truck makers, truck owners and the federal government have struggled to come up with a consistent rating scheme for brake materials that meaningfully relates to their on-vehicle performance. The American Trucking Associations petitioned NHTSA some 20 years ago to work out such a rating system.

In 1989, NHTSA agreed to consider beginning rulemaking to develop a standard for marking, identifying, and rating the effectiveness of heavy-truck brake linings. Then the agency embarked on a number of studies to determine the feasibility of doing this. It dropped the rulemaking in 2002, deciding it was unlikely that a suitable test procedure for comparing and rating brake linings could be developed with available test equipment and procedures.

In 2002, NHTSA began looking for procedures that work. The Oak Ridge National Laboratory has been working on it, with assistance from the Heavy Duty Brake Manufacturers Association and ATA.

There are a lot of challenges involved, Hawker says. For one thing, he says, "some friction manufacturers simply don't want to participate. Participation does require resources and adds cost, as well as the fact that some of the available friction products simply don't perform as advertised."

The research group is testing friction materials, measuring torque output at 10-, 20-, 30-, 40-, and 50-psi stops. A recent addition to the research will include a series of stops, say 100 stops at 10 psi, then pull the wheel and measure the lining wear, Hawker says.

"It's going to take years, not months, to get all the testing done, to put a graded factor on a brake block," he says. "Then that graded factor's going to have to be changed as you change the size of brake. The result is a massive project. You've got every size brake, every width, every diameter; each has to be tested in order to put an evaluation number on it. Nobody in the testing arena realized how in-depth this would get."

And growing acceptance of air disc brakes opens the door for a whole new series of aftermarket friction material testing.

In the meantime, the industry has tried to address the issue with the Technology and Maintenance Council's Recommended Practice 628, "Aftermarket Brake Lining Classification."

This RP outlines the 40-psi torque value for certain linings as tested in compliance with FMVSS 121. These ratings are listing in a publication overseen by the SAE Brake Lining Performance Review Committee and published by TMC. Not only are linings listed; certain of the products are checked each year to see if they perform as indicated.

While RP-628 was a major accomplishment, it's still just a start. For instance, Hawker says, the RP focuses on a 40-psi brake application. "The trouble is, 80 percent of our stops are using 20 psi or less. Torque output is not linear; just because it puts out X amount of torque at 40 psi, doesn't mean it's going to put out half of X at 20. It doesn't work that way."

The RP also doesn't help you determine the effectiveness rating of the worn lining you're trying to replace. Neither does it give the effectiveness of any new lining. It also is of no help with brakes that are a size other than 16.5-by-7-inch. On top of all this, it's voluntary.

You Get What You Pay For

Beyond the issue of making sure the brake linings you buy match what was originally on the truck, there's the issue of the quality of the linings themselves. There are many aftermarket brands available, and while there are certainly many quality brake linings out there, there are many that are not.

When done right, it takes two or three years to fully develop a friction material. Batteries of tests on dynamometers, in labs and on tracks help manufacturers fine-tune a material until it performs as desired in that particular application. It may take 50 to 100 iterations of a material before the right recipe is found.

But that's not the case with all linings – especially with low-cost brake linings coming in from overseas.

"There's a direct correlation in the aftermarket, and has been for years, between the price and the quality of the lining," says Peter Freeman, senior product manager for air brake product in the aftermarket for ArvinMeritor. "It's always been held up true that the lower the cost, the cheaper price the friction material is, the lower quality it is."

Not only does the price reflect the friction materials and the research it takes to develop them, but also quality testing during manufacturing.

Haldex's Petresh doesn't mince words: Compounding the brake lining issue, he says, "is the crap that's coming in from overseas. That stuff in a lot of cases is not only not equivalent, but it's not acceptable and even downright dangerous in some cases – kind of like all the bad press we've been seeing with tires and toothpaste and dog food." On the automotive side, counterfeit brake linings made of things such as sawdust and compressed grass have caused fatal crashes.

What Can You Do?

The most foolproof way to make sure your brakes perform as designed is to replace worn brake linings not just with new linings, but with new brake shoes and linings from the original equipment manufacturer.

"Even if you order new brake shoes, unless you're also ordering brake lining based on FMVSS regulations as well as your axle weight rating, performance and life expectations, you're not necessarily going to get the friction material that will meet your application requirements," says Bendix Spicer's Hawker. "Dealers and distributors can't stock the many different formulations of brake block required to meet every application, so what they do is focus on the most common. This may get many fleets 'close,' but in today's trucks, close isn't good enough."

Hawker says two major fleets he works with have stopped using relined brakes. While this costs more per replacement than a typical reline brake job, he says, these fleets have found that in the long run, this strategy leads to the lowest cost per mile.

"When they do a brake job, it's not just slip another set of shoes on it and send it out the door," he says. "They do the complete brake job – they inspect the brake chamber and replace if necessary, take the slack adjusters off and inspect them and replace them if necessary, put new bushings on the cams, and so forth, and basically when this thing goes back together, they have renewed the wheel-end to a like-new condition, and it performs like a new brake. When you renew or remanufacture the wheel end back to OEM specs, it guarantees you've got the brake performance you want."

While this approach is gaining more fans, most truck owners are still going to want to replace just the linings. "Most everybody replaces with aftermarket materials, which can bear no resemblance to what they took off," says Haldex's Petresh.

There are several steps you can take to do this and make sure you have the best-performing brakes possible:

1. Find out what the truck was built with initially. "It's not painted on the dashboard or on the doorjamb, but you can go to the OE, go to your dealer, and find out exactly," Petresh says. "While it's not simple, easy or convenient, it's still doable."

2. Refer to TMC RP-628. This provides a database of materials that have been tested and approved per specific procedures for aftermarket usage. While it has its shortcomings, at this point it's the only real document out there providing any guidelines. If you don't belong to TMC, you can download the most recent listings from the Performance Review Institute, which administrates the testing program, at www.pri-network.org/Brake-Lining-Program.id.29.htm.

3. Don't buy just on price. "Saving a few cents on the lining can cost you a lot more if a DOT inspection finds a problem with it and you have to do unscheduled maintenance," says ArvinMeritor's Kay.

A good strategy is to stick with recognized name brands from companies with a good reputation, and work with a company that has the knowledge to help you select the right replacement lining.

"Deal with people you know, people that have a reputation of being a first class manufacturer – not Joe Schmoe Friction Company," Petresh says.

Bendix Spicer's Hawker says the industry is seeing the demise of the reliner who would just take discarded shoes, punch out the rivets, give it a quick coat of paint and rivet on any type of lining. "That type of operation is slowly but surely dying. Everyone in the industry is getting more educated on the risk and true cost of a low-priced relined brake show. They don't want the liability of putting on something that's not backed by a major manufacturer."

Wayne Stockseth, president of FleetPride's Parts Distributing Co., agrees that with brake linings, you tend to get what you pay for. "The better quality brake lining, like most better quality things, cost a little more money." Unlike some other products, he says, "the price varies, not because of the brand name or the jazziness of the marketing program, but because of the stopping power and the wearability of that lining."

Stockseth says when a customer comes in and asks to buy the cheapest brake lining possible for his size of brake shoe, that's when it's time for some education. "This is one subject that really needs to be discussed with the customer on what kind of service they are in. For instance, if you're a tanker with shifting loads, you need a friction material that has better stopping qualities than a dry van running down the interstate."

"Be an educated consumer," says ArvinMeritor's Freeman. "If you're approached by somebody telling you they've got a better material, you should consider things like where it's being manufactured, the test data that's available to you, the manufacturer's liability, all those type of things that you need to be careful about on a safety-related product like brakes."

One thing that could change the whole brake lining situation would be increased use of performance-based brake testers (PBBT) in enforcement efforts.

A PBBT assesses vehicle braking capability by measuring brake forces at each wheel, or by measuring overall vehicle brake performance in a controlled test. Five years ago, the Federal Motor Carrier Safety Administration issued pass/fail criteria in a rule that allows motor carriers and federal, state and local enforcement officials to use PBBTs to determine whether a truck's brakes comply with Federal Motor Carrier Safety Regulations. These devices include certified roller dynamometers, breakaway torque testers and flat-plate testers.

"If they became more prevalent, you would see a major change in a hurry in the industry," says John Hawker, service engineer with Bendix Spicer Foundation Brake, "because your brake decel would be measured at a weigh station. Much of the problem with undesirable brake product would go away. I've seen them demonstrated, they work well, but it hasn't gotten off the ground."

The federal rule allows PBBTs to be used in enforcement efforts, but did not require that failing a PBBT be grounds for placing a vehicle out of service. The Commercial Vehicle Safety Alliance has considered the issue, but in a close vote two years ago, decided against it.

That's largely due to resistance from the American Trucking Associations, which has some concerns with using PBBTs to put trucks out of service.

In a letter to CVSA's newsletter in 2006, ATA engineer David Nguyen noted that while the association supports the use of PBBTs for assessing vehicle braking capability, it opposes their use for placing vehicles out of service.

"Given existing technology, PBBTs cannot take the place of visual inspections. Because PBBTs lack visual inspection of a truck's brake components and other hardware, an unsafe truck could pass a PBBT test, placing it in service, having not undergone a Level 1 inspection."

ATA also contends that these machines have demonstrated as much as a 30 percent variability on certain wheel ends, with wet conditions especially prone to create misleading readings.

Advocates of PBBTs point to their benefits in fleet use. For instance, one company that performs analyses of braking using a performance-based brake tester checked 47 owner-operator maintained vehicles for a client. The machine rejected 51 percent of them for having unsatisfactory brake power. Thirty-two percent had low braking power, and 19 percent had power so high that there could be tractor-trailer compatibility problems. Many of these vehicles' problems stemmed from brake linings.

Performance-based brake testers, especially dynamometers, have often proven valuable in diagnosing hard-to-find brake problems, such as poor drum/lining fit, contaminated linings, broken park springs, broken or out-of-round drums, kinked air lines, defective valves and cross-wired ABS sensors. Plus PBBT results can back you up in court, offering proof that the brakes were working properly.