At Starbrite Trailers, we understand the significance of reliable braking systems for heavy-duty trucks. Your brakes ensure safety of both you and others on the road, while also increasing performance. However, hidden brake threats can undermine your operations, leading to costly downtime and repairs. Here are five hidden brake threats that every truck driver and fleet manager should be aware of to keep those hauls running smoothly. Strap in and prepare for a journey and learn about your truck's braking system.
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An air brake system relies heavily on a well-maintained, leak-free air supply. Even minor leaks can significantly reduce brake efficiency, increasing stopping distances and risking brake failure. Common causes include worn or damaged hoses, loose connections, and faulty air dryers.
To uphold optimal air system functionality, it's essential to conduct thorough inspections regularly. This includes inspecting hoses for signs of wear or damage, ensuring all connections are secure, and verifying the operational efficiency of the air dryer. Replacing any worn-out hoses and securing loose connections are pivotal steps.
Additionally, a properly functioning air dryer is crucial for minimizing moisture in the system, which helps to prevent rust and the freezing of lines during colder months. By implementing these preventive strategies, the longevity and reliability of the air brake system are significantly enhanced, promoting safety and efficiency in your fleet's operations.
Slack adjusters are essential components in ensuring the optimal functioning of braking systems in heavy-duty trucks. They help maintain the correct clearance between the brake shoes and drums. Misalignment or improper adjustment can result in uneven braking force distribution, which not only causes uneven wear on brake components but also reduces overall braking effectiveness.
It is vital to conduct regular checks and adjustments on slack adjusters to confirm they adhere to the manufacturer's specifications. While automated slack adjusters offer convenience by self-adjusting, they still require periodic inspections to ensure their mechanisms are functioning correctly and have not deviated from optimal settings. During these inspections, it's also important to look for signs of wear or damage and to replace any components that are not performing as intended. This proactive approach helps prevent more significant issues down the line, ensuring safety and extending the life of the brake system.
Brake shoes are critical to the braking system of heavy-duty trucks, particularly when dealing with intense driving conditions such as long descents or carrying heavy loads. When brake shoes become glazed, their surface turns smooth and hard, akin to glass, due to the high levels of heat and friction generated during such conditions. This glazing severely impairs their friction capabilities, leading to a notable decrease in brake performance.
To ensure your vehicle remains safe and responsive, it is essential to inspect the brake shoes regularly for any signs of glazing. Look for a shiny, hardened surface which indicates that the brake shoes have been compromised. Upon detecting any glazing, it is crucial to replace the brake shoes without delay to restore full braking functionality. Additionally, promoting proper driving habits that minimize sustained heavy braking can significantly help in preventing brake shoe glazing. Regular training for drivers on the optimal use of brakes can also extend the life of brake shoes, enhancing overall vehicle safety and efficiency.
Brake linings are crucial for the effective operation of braking systems in heavy-duty trucks, but their performance can be severely compromised by contamination. Common contaminants include oil, grease, and dirt, which can drastically reduce the friction needed for proper braking. Such contamination typically results from leaking wheel seals or from neglect during routine maintenance procedures.
To ensure the safety and reliability of your braking system, it's important to inspect brake linings and their adjacent components regularly for any signs of contamination. Should you discover contaminants, it's crucial to clean the affected area meticulously and replace any contaminated brake linings immediately. Additionally, checking that wheel seals are intact and free from leaks is essential to prevent future contamination. By maintaining these practices, you help ensure optimal braking performance and extend the lifespan of the brake components.
Brake chambers are pivotal in the operation of air brake systems on heavy-duty trucks, transforming air pressure into the mechanical force that applies the brakes. When these chambers malfunction, it can manifest as air leaks, uneven braking pressure, and in severe cases, complete brake failure. Two frequent culprits of such issues are tears in the diaphragm and misalignment of the push rod.
To prevent these hazardous conditions, it's essential to conduct regular and thorough inspections of the brake chambers. Look for signs of physical damage, wear, or symptoms of air leakage, which could indicate a compromised chamber. If any abnormalities are detected, replacing the faulty brake chambers promptly is crucial to ensuring the vehicle's braking system remains highly functional and safe. Regular maintenance checks not only safeguard against unexpected brake failure but also contribute to the consistent performance and longevity of your truck’s braking system.
Recognizing potential issues with your truck's air brake system can prevent breakdowns and ensure safety. Look for these signs:
Regular inspections and maintenance are vital. Ensure your brake system is thoroughly checked during routine maintenance, and address any abnormalities immediately.
Whether a fleet’s assets are configured with air disc brakes (ADBs), drum brakes, or both, one aspect bridges across all specifications – friction material. The friction material, or brake lining, serves a particular role no matter the braking system configuration – to bring the vehicle to a stop. Understanding the needs of the fleet and the maintenance considerations associated with brake lining will help a fleet establish an efficient operation, and maximize the life of the friction material as well as vehicle uptime.
“Brake linings are one of the essential elements required in stopping a truck,” says Abe Aon, business leader – Fleet Solutions, North America, ZF Group Commercial Vehicle Control Systems. “When a truck is utilizing a drum brake assembly, the brake linings are forced against the drum to slow the vehicle. On a truck utilizing disc brakes … the friction pad material is pressed against a rotor from both sides using a clamping motion from the brake caliper to slow the vehicle.”
In order to stop or slow a vehicle, the brakes must expend kinetic energy, says Keith McComsey, director, air disc brake and systems, Bendix. The frictional force of a braking system resists motion, which in turn generates heat.
“It slows that spinning part down, which then slows the vehicle down,” McComsey explains. “Whether you have air disc brakes or drum brakes, it doesn’t matter. They both, in similar principles, apply mechanical force that applies frictional material against a spinning mass, AKA the drum or the rotor, which then generates that frictional force and slows the vehicle.”
Friction material varies in composition.
“Friction materials may have five different components,” says Eric Coffman, senior product manager at Meritor. “Your first one is typically a structural package; a lot of times that is fiberglass. Then you have your resin, which is your glue. Then you have a filler, which basically takes up space in the material. There are lubricants and abrasives, which collectively are called friction modifiers.”
Coffman explains that the friction modifiers such as different grades, shapes, and sizes of copper, steel, fiber, graphite, steel powder, aluminum oxide, among others, determine the friction material’s characteristics.
“How you take these materials and blend them together, and in what quantities and ratios, will give you those characteristics of either high brake torque, or maybe … long brake life, or resistance to noise, et cetera,” Coffman continues. Further, Coffman says that the quality of resin can affect the friction material as higher quality resin will handle higher temperatures.
After finalizing a blended formula, brake lining manufacturers put the material through rigorous testing to determine its performance capacities. In the case of Meritor, Coffman explains that friction material typically goes through 50 to 80 dynometer tests in order to be validated at different brake sizes and weight ratings. During these tests, brake torque, fade, noise, and other parameters are measured and assessed.
“Then it will go on a fleet test for 18 to 24 months,” Coffman says of tested brake linings. “Typically, we try to get two winters in a fleet test, [as well as] track testing certifications.”
Reduced stopping distance (RSD) regulations have made it necessary for brake lining and component manufacturers and OEMs to introduce various friction material spec’ing options in order to achieve the required reduction in stopping distance. Different methods were used though the goal was the same.
“Bendix managed getting that reduced stopping distance by pushing more of the brake torque on the steer axle,” Bendix’s McComsey says. “We went from an organic material to a semi-metallic material on the steer brake. Other manufacturers managed that by changing the size of their shoe without changing the lining material. Each brake manufacturer approached it a little differently.”
“In the past, the steer axle did less work than the drives in terms of bringing the [combination vehicle] to a stop,” Meritor’s Coffman relates. “The secret sauce of RSD is getting that five-inch steer axle brake to perform like a seven-inch brake. That’s done through having a more aggressive friction material, as well as some other system changes.”
“Different linings are used between axles,” ZF’s Aon explains. “The steer axle, in general, will not create as much brake force and will usually have a lighter axle rating than the drive axles. As a result, a less aggressive friction material could be used. Drive and trailer axles do most of the brake ‘work’ and the friction material is based on the axle ratings of those axles.”
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But there is more to keep in mind than just meeting a certain stopping distance when considering friction material.
“Regional route vehicles generally will use their brakes more frequently based on the nature of their routes compared to long haul vehicles,” Aon says. “As a result, regional route vehicles will create more heat due to the frequency of them using their brakes and should use a lining that is designed to regularly reach those higher temperatures. Off-road or refuse vehicles will also need to match their higher axle ratings with a higher temperature rating for their application. In some cases, these applications will use a form of metallic in their linings.”
Different vocations, applications, and duty cycles play a major role in determining the appropriate friction material, as well as impact the life and performance of that friction material.
“This is the most extreme example, but I like using it,” Coffman says. “If you’re running a refuse fleet and you put a low-end 23- or 20,000-pound brake lining on it, you’re going to see super accelerated wear because that material does not wear well at a high wheel-end temperature. On the flip side, if you’re the guy that runs a van trailer across Kansas and you’re hauling packages that are mostly air, you might be able to get away with a lower-end material and not really have that big of a deal because you don’t hit the brakes that often.”
When it comes time to select replacement friction material, brake manufacturers have tools, resources, and recommendations to assist fleets in finding what fits best for their operations.
Meritor offers MeritorPartsXpress.com as an online tool to help fleets running drum brakes through the challenge of finding a lining that fits their brake shoes. Coffman explains that after entering details such as manufacturer, a few measurements in critical dimensions, and even vocation, MeritorPartsXpress.com will display a list of applicable linings that are available and suitable.
“On the air disc brake side, it’s a little more simplistic because the variations are focused on more of the brake duty cycle rather than geometry and some of the other things that impact things on the drum side,” McComsey says of sourcing appropriate friction material replacement. He also recommends replacing like-for-like when it comes time to replace the brake lining.
“Whatever came on the vehicle already has a part number associated with it, and you can get that from the OEM or request that through various distributors,” McComsey says. “And that is really the best way to ensure a couple of things. One, it ensures that you maintain the proper brake performance as was designed and tested by the OEM. That [also] ensures proper fit and consistent performance.”
McComsey warns that should a fleet change friction away from like-for-like, it may have unintended consequences. A driver that has gotten used to how a vehicle performs may experience changes in braking performance, or the stopping distance may be different than it was with the OEM-supplied friction material.
Getting the right friction material on the asset is one thing; getting the desired performance and maximizing its life while minimizing unnecessary downtime is another matter entirely. A best practice is to manage brake lining performance through tracking and recording wear. The ideal setting to track and record wear happens when a truck operates with similar mileage, routes, loads, duty cycles, and vehicle operator. With as few variables included as possible, a correlation between mileage and lining wear should present itself.
Recording lining thickness measurements at specific intervals will create a data set. Over time, this data set can provide insight into how many miles cause how much wear. Analyzing this data and cross referencing it to established maintenance schedules and practices, particularly preventive maintenance (PM) inspections, can allow fleets to align brake lining services with other necessary maintenance in order to avoid bringing in an asset and racking up downtime for singular services.
Bendix’s McComsey further advises replacing like-for-like by reminding that if a fleet has been tracking wear and associating it with mileage and then chooses a different friction material, “all that data goes out the window and you’re starting from square one.”
Most friction material is manufactured with a wear indicator; utilizing the wear indicator should allow fleets to coordinate replacement intervals after understanding the status of remaining material available.
To assist in wear measuring efforts, Bendix developed Pad Wear Sensing for the company’s ADB22X Air Disc Brakes. Pad Wear Sensing monitors the brake pad thickness and provides a warning without technicians having to physically measure the friction material.
“The system has sensors built into the pad friction [material],” McComsey says. “When the pad friction gets down to a certain thickness, it creates a signal that ultimately gets picked up by telematics through ABS [the anti-lock braking system], or through an ECU [electronic control unit] in the chassis system.”
With such technology, fleets can expect when the brake lining end-of-life is approaching while there is still material remaining, allowing the fleet to effectively schedule service, McComsey says. “The fleet can effectively schedule their maintenance to be more efficient, and when they’re bringing their vehicle in for maintenance, maybe they can combine that with other things at the same time,” he says.
Regular lining wear is not the only aspect to be noted.
“Periodic wheel-off inspection is still required because the wheel-on measurement only checks the outer pad,” ZF’s Aon says.
He further recommends examining the surface of the friction material beyond just its thickness, as glossy or cracking surfaces may be indicative of other issues.
“The lining will often tell a story of other components that may need your attention,” Aon says. “For instance, if a technician notices uneven wear on the pads when he or she is replacing them, they should look into the drum or rotor and replace them if necessary. A technician should check for abnormal wear of the lining to the drum or rotor. In addition, it’s recommended to take a close look at all the boots and make sure the caliper moves freely while the pads are out.”
Other best practices in maintenance will assist in brake lining performance and longevity. McComsey recommends any areas where brake shoes make contact be cleaned when in for service.
“Those things get bombarded with contaminants, as far as road wash and spray, road grime, [et cetera], and over time as things heat up and cool down, there are paths for contamination to get into those components,” he says.
McComsey advises fleets lubricate brake system components any time they have the opportunity.
“When you’re lubricating them, you’re basically purging the old grease out, so with the old grease comes the contaminants,” he explains. “You’re basically breathing new life into those components so that they last longer and continue to operate properly. Get any kind of contamination off that might interfere with how the shoe sits in the rollers, in the cam pocket, and take the opportunity to check the S cam for play. Look at the seals for any kind of grease leakage.”
Meritor’s Coffman seconds McComsey’s recommendations, emphasizing monitoring the cam shaft and bushings, along with the slack adjustment.
“Axial and radial cam play is either a worn camshaft or worn cam bushing, and those can manifest themselves in different friction issues,” Coffman explains. “Axial cam play can give you some noise. Radial cam play can mess with your brake stroke and mess with how your shoe ends up contacting the drum if you get too much movement there. Check your slack as well as your foundation brake setup to make sure that you’ve got enough running clearance. Some excessive wear can be indicative of something that was set up too tight initially. If you’ve got it set up too tight, you don’t have enough running clearance and you can get some brake drag and get some wear there.”
Coffman warns about the manner in which the camshaft tolerances are measured. If axial and radial play measurements are taken with the slack attached and/or after greasing the camshaft, the technician can get a false reading showing the system is tighter and in better health than it actually is.
Deliberate maintenance practices and diligent monitoring of wear will keep technicians and the fleet informed and ahead of impending failures. With the needs of the fleet determined, specification is just the first step in adequately utilizing the most appropriate friction material. Tracking wear and establishing a data set will help a fleet build efficiency in their operations and meet performance expectations. Coordinating all factors will help to maximize the brake lining life and create a maintenance schedule that maximizes uptime.
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