HOW important is it to replace brake assemblies with like shoe and lining assemblies to maintain braking capability?
“Our strongest suggestion is replace like for like,” says Randy Petresh, vice-president of technical services for Haldex. “That’s your best choice. That way you’ve got at least a good chance of getting equivalent performance after you do the reline, unless you’re a very astute owner-operator or mechanic that knows brakes that well that you can make a material choice over and above what you’re using. That’s usually a ticket for doom.
“The smart guys rely on their suppliers and contacts to give them the right answer or the right guidance. Just buying something over the counter is usually is a 50-50 proposition, unless you know what you’re requesting or are talking to somebody who knows the answers to all the questions for the equipment you’re operating.”
Says Tim Bauer, director of undercarriage products for Meritor’s aftermarket business, “From a braking performance standpoint, that’s the only way to restore brakes to the original performance, so we do recommend fleets do that.”
And it’s especially important because of the Reduced Stopping Distance (RSD) mandate. Phase One took effect in August 2011 for new three-axle tractors with Gross Vehicle Weight Ratings (GVWRs) up to 59,600 lbs. Phase Two of the mandate, aimed at tractors with two axles, as well as severe service tractors with GVWRs above 59,600 lbs, took effect August 1.
Even though two years have passed since the RSD mandate went into effect, Bendix still regularly fields questions from fleets and drivers about replacement brake-lining performance and RSD compliance, according to Gary Ganaway, director of marketing and global customer solutions.
“There’s a lot of misinformation to sift through concerning the certification of aftermarket brake linings and today’s high-performance brakes, so the industry’s confusion is understandable,” he says. “It’s important for everyone to understand the impact that friction selection has on safety, and that not all replacement friction marketed as acceptable under RSD will actually perform to the standard.”
According to Ganaway, the long-time industry standard test for certifying brake linings, Federal Motor Vehicle Safety Standard (FMVSS) 121, is no longer adequate in the RSD environment. He said that most linings that pass the dynamometer requirements do not meet today’s higher vehicle performance requirements.
To illustrate this, Bendix compared the 60 mph stopping distance of an RSD-compliant vehicle equipped with high performance brakes and linings against several pre-RSD OEM and aftermarket brake linings that passed FMVSS dynamometer certification. The RSD-compliant vehicle used Bendix High Performance ES (Extended Service) brakes and consistently delivered a stopping distance of 215 feet—well under the 250-foot limit established by the federal mandate.
None of the comparison friction used in the relining of the RSD brakes—materials readily available in the aftermarket—met the mandate’s stopping distance requirement. And the worst-performing friction material—a popular aftermarket lining—had a stopping distance of 311 feet. The 96-foot difference between that and the high performance friction represents a 45% decrease in performance—or approximately five passenger car lengths.
“Nothing could more starkly depict the highway safety that is at stake, and the importance of using the right friction when it comes to relining high performance, RSD-compliant brake systems,” Ganaway says. “Although advancements made in brake engineering and friction material in recent years have significantly improved both safety and performance, those steps forward can be dangerously undermined through relining today’s brakes with improper friction material.”
Technicians relining Bendix brakes will soon see something new within the wheel end: Bendix high-performance brake shoes will now carry a warning label to help educate the commercial vehicle industry about crucial performance issues related to relining.
This Bendix brake is designed to meet the Federal Mandate for Reduced Stopping Distances and, where necessary, is equipped with special reinforced shoes. These brake assemblies must be replaced with like shoe and lining assemblies to maintain braking capability. Failure to do so could negatively impact the safe operation of this vehicle.
Bauer says Meritor has a label that outlines what part number should be ordered for replacement.
“That’s so that the vehicle operator gets the exact same thing, which is what we recommend they do,” he says. “It delineates the aftermarket part number they should be ordering. It’s not a unique product number. We went to a smart number that identifies the friction material and brake size right on the label.”
Meritor performs an extensive testing and certification process before its friction material is recommended to the OEM, running as many as 100 different tests to ensure consistent performance.
The first is lab testing of materials to make sure the material selected is the optimum choice. These include swell and growth tests, and substance testing, to ensure that substances in friction materials are environmentally safe; strength testing against cracking and wearing; and noise/vibration/harshness (NVH) testing.
The second test set is dynamometer testing, which includes extensive performance testing that simulates actual road conditions. Once the dynamometer testing is complete, vehicle truck testing begins on the test track. Meritor tests its friction materials to meet or exceed FMVSS 121 and then conducts fleet testing in real-world conditions, using several different vehicle types and applications. This includes all of the terrain and weather conditions that are needed for a wide range of vehicle conditions.
Meritor requires an additional 10% shorter stopping distance than the FMVSS 121 regulations require. For example, if the federal government requires a stopping distance of 250 feet, Meritor targets 225 feet. This extra measure of performance provides a buffer to ensure that all vehicles are compliant regardless of tire size, wheel base, axle load, or other specific vehicle requirements.
Once all test measures are satisfied, Meritor provides the friction materials to the OEM to install on new trucks for testing, including all test data reports. When all test results are mutually agreed upon by Meritor and the OEM, Meritor then releases the friction into production and service for distribution for fleet consumption. Once all these parameters are met, the material is then granted MA designation.
Meritor’s aftermarket network also offers MG and Fras-le friction materials that meet all FMVSS 121 requirements for stopping performance. The MG line includes CG friction materials, which feature attractive pricing for refuse vehicles, logging trucks and off-road applications with consistently high drum temperatures.
Meritor suggests that those looking for the correct friction mixes need to understand a few items:
- Application. What is the truck trailer vocation? On- highway, off-highway? Load?
- What is the axle rating? 20,000? 23,000?
Meritor’s recommendation would be to replace with the same materials that came on the vehicle and do a complete and proper brake job per Meritor specs.
TMC’s RP628 is a source of information that some fleets use.
Some of the steps:
- Use the lining material specified by the vehicle manufacturer to help ensure brakes perform correctly and meet Department of Transportation (DOT) regulations.
- Always reline both wheels of a single axle at the same time.
- Always install the same type of linings and drums on both wheels of a single axle.
- Always follow the vehicle manufacturer’s specifications for brake friction material. Friction material requirements may not be the same for each vehicle.
Haldex’s Petresh believes the lining is only one part of the equation.
“Selection of the proper or appropriate material for a certain condition, application, or brake configuration is really the key, not each individual component,” he says. “There are other very essential parts of that equation, like the brake adjuster arm length and chamber size, that create the brake force and power for an application that contribute at least as much to the equation as the friction material itself.
“If you make the wrong choice or don’t make an intelligent choice at all and use any old thing, yes, it will have a bearing. But it’s not a function usually of the friction material itself—not unless you buy stuff from overseas, what I call the K-Mart Blue Light Special, with no identifying marking or anything on it, and you have no idea what it is. If you’re using that, it’s a different story. You can’t pick a stopping-distance lining versus non-stopping-distance lining. You select the right material in combination with other things to give you the performance level you need.”
He agrees that most linings that pass the dynamometer requirements do not meet today’s higher vehicle performance requirements.
“Dynamometer performance is one of several indicators of a friction material’s performance capabilities and characteristics,” he says. “But the material is rated for a specific brake with a specific combination of brake power. In other words, brake adjuster arm length and chamber size, and for a certain axle or wheel GAWR rating.
“I could take friction XYZ and somebody could say that’s great. It passes all tests and meets 121, and maybe it’s tested at 20,000 pounds with a certain size adjuster or chamber. OK, it’s good for that combination of components and that brake size and that axle GAWR. If you were to run a heavier load, it wouldn’t be adequate, and if you were running a significantly lighter axle load, you’d be overpowering the brake and causing other problems.
“It’s a very narrow definition. You rate a material for the conditions and brake size and axle loadings that it was compounded for, developed for, and tested for. Too much friction is not good. Too little is not good. There isn’t any simple answer for a lot of these things.”
Questions and answers:
Meritor has published a white paper on how the reduced stopping distances requirements are affecting both parts departments and OEMs. Below are the most frequent questions the brake manufacturer has been receiving, along with the advice it has been giving:
Q. Can a fleet retrofit all of their brakes to the new Meritor RSD friction materials?
A. Rear brakes can be retrofitted seamlessly from existing materials to the new Meritor RSD friction. Meritor RSD friction materials may increase torque in older front brake designs and affect the integrity of older front spiders with 5/8” bolts.
Q. Will the use of RSD friction materials on vehicles with older brakes improve the stopping distance of those vehicles or increase the wear life?
A. Retrofitting tractors and trailers with older brake designs to the new Meritor RSD friction materials will have no impact on vehicle stopping distances. Stopping distance and wear will be comparable to existing friction materials.
Q. By what distribution channel will Meritor Aftermarket supply new RSD friction materials?
A. New Meritor RSD friction materials will be available only on new or reman lined brake shoes and brake shoe kits from the authorized parts outlets, such as OE dealers or warehouse distributors.
Q. Will the new stopping distance regulations require air disc brakes?
A. Both drum and disc air brakes systems may be used to meet the requirements.
Q. How will fleet operations and vehicle specifications change?
A. A fleet continuing to use drum brakes will see minimal changes to operations and service practices. In most cases, drum brakes will remain standard equipment. In instances where larger brakes are required, Meritor has lightweight component options, including stamped steel spiders and SteelLite X30™ brake drums to help mitigate weight increases.
Meritor service practices will not change. Service technicians and mechanics will not have to be retrained on maintenance of the Q Plus brake.
Q. Are reduced stopping distance drum brakes available for vehicles not impacted by the revised regulations in August 2011?
Because there are common brake sizes between vehicles affected by the regulations, and those not affected by the regulations, there are RSD materials that would be available. However, vehicle braking performance will not be improved by using the new materials on older vehicles.
Q. What is the new FMVSS 121 stopping distance requirement and when does it take effect?
A. Phase 1 of the new RSD requirement took effect August 2011. It required new three-axle tractors, (with gross vehicle weight ratings up to 59,600 lbs.; from 60 mph), to stop within 250 feet loaded and 235 feet unloaded.
Q. What is the requirement for other types of vehicles such as straight trucks and buses?
A. New requirements for other types of vehicles are part of Phase 2, effective August 2013.
Q. What is the impact on existing vehicles?
A. The law only affects new production tractors. There is no legal requirement to retrofit older vehicles, yet many fleets of all sizes opt to use the RSD lining on their existing fleet population.
Q. How is compatibility affected between tractors equipped with the new Meritor RSD friction materials and trailers with older brakes and friction materials?
A. Tractor-trailer brake compatibility was a design requirement for the new Meritor RSD friction materials. The tractor will incur approximately 5% more of the braking workload, while the trailer will experience a proportionate reduction in workload.
Q. Regarding the new Meritor RSD Q Plus brakes, what has changed other than the friction material?
A. Because front brakes now absorb more brake torque, the front brake spiders have been made heavier and the mounting bolts are a larger diameter. Front brakes now use Type 24 brake chambers, increasing the AL factor to 132.
Q. Are larger brake sizes required to meet the new RSD requirements?
A. Not in all cases. Meritor has worked with all of the major vehicle OEMs to design the brake package to meet the new stopping distance requirements. Brakes may be slightly different from one OEM to another. See the Meritor application charts for specific sizes per OEM.
Q. Are there advantages to using larger brake sizes?
A. Larger brakes will provide some advantages, including increased lining volume to drive longer service intervals, lower operating temperatures, reduced fade and improved performance.
Q. Will my service practices have to change?
A. Drum brake service practices do not change. Service technicians and mechanics will not have to be re-trained and parts inventory practices will transition to the new drum brakes. However, new parts and friction, including new brake shoe FMSIs and hardware kits corresponding to the new brake sizes, should be stocked at fleets or authorized parts outlets. ♦