Top brake questions, answered - Fleet Equipment Magazine

The No. 1 job of truck brakes is safety; within that application, there’s more than one way to stop a truck. Drums have been the brake of choice for many trucks, but air disc brakes (ADBs) continue to gain popularity in nearly all heavy-duty on-road applications.

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“Current [ADB] market penetration is in the 12% to 15% range for power units and 8% to 10% for trailers,” said John Thompson, sales manager CV NAFTA, for TMD Friction, supplier of commercial vehicle brake friction, brake pads and linings to both the OE and aftermarket sector. “Installations are increasing and it is currently believed that penetration will level off in the 20% range in the next five years. Some OEMs are standard with steer axle disc brakes, and upcharges for spec’ing disc brakes have reduced somewhat. These trends, coupled with improved performance over cam brakes, will help increase market penetration.”

Fleet Equipment talked to the top minds in the brake and friction markets to get the answers to the most asked brake spec’ing questions.

Let’s talk application—what type of brake is going to be best for my applications?

When it comes to application, all brake systems will be impacted by the service environment, frequency of use conditions and quality of components utilized.
“For applications that carry more load, have more frequent stops, see more off-highway or off-road activity and/or are exposed to weather extremes, fleets have found it beneficial to select more robust drum brake systems with larger pad widths or more aggressive linings,” says Bill Hicks, director of product planning/Market Development, trailer suspension business unit, SAF-Holland, which offers a full brake product portfolio for heavy-duty trailers and some auxiliary axle applications. “Disc brakes provide the ultimate answer to the most difficult applications with their inherent superior brake fade resistance to mountainous or steep grade routes or other situations where the fleet is concerned with enhanced safety and durability.”

That said, brake life cycles vary wildly due to numerous factors across many applications. Alex Wieczorek, Stemco’s segment business leader, brake products, recommends that fleets should consider the route the vehicle travels (city, over the road, rural), the average load of the vehicle (heavy or lightly loaded), the terrain (flat, hilly or mountainous) and the driver’s experience level. “Understanding these factors and choosing brake components that correctly match the vocation of the vehicle such as over the road, tank/bulk haulers, refuse/construction and transit bus will help extend these brake intervals,” he explains.

I’ve been using S-cam drum brakes for years, why should I make the switch to ADBs?

Bottom line: ADBs provide shorter stopping distances with virtually no brake fading, side-to-side torque variation or other problems. They also typically last 50% to 100% longer than drum brake counterparts, according to Gary Ganaway, director of OE and technical sales for Bendix Commercial Vehicle Systems.

Across all the wheel, brake and friction companies we talked to—Abex Commercial Grade Friction manufacturer Federal-Mogul Motorparts, Bendix, Meritor North America, Haldex Brake Products Corp., SAF-Holland, Stemco, TMD Friction and WABCO—agree that ADBs provide the maximum stopping power.

“The greatest benefit of air disc brakes is their ability to provide consistent torque levels—meaning essentially no fade—across a very broad range of operating temperatures,” explains Tom Rogers, senior applications engineer, Commercial Vehicle Friction, Federal-Mogul Motorparts. “Traditionally, this has made air disc brakes popular in specialized applications like fire trucks, commuter buses and some city buses. With the advent of RSD regulations, however, more fleets are considering air disc brakes for steer axles that will be matched up with drive axles equipped with drum brakes.”

“The braking feel is more like that of a passenger car, which is one reason why more and more truck drivers appreciate them,” adds Brent Fitch, director of fleet sales for WABCO, which focuses on its ADB offering with its MAXXUS products that exceed stopping distance regulations by more than 15%, according to the company. “To us the future of braking in this industry is disc brakes.”

You’re also looking at lower overall total maintenance for the life of the brake due to longer service intervals. (More on that in a minute.)

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So what’s the ADB catch?

You probably already guessed it: Cost. The initial cost to spec ADBs comes at a premium. According to Bendix’s Ganaway, the cost of ADBs is, approximately, a $600 per axle premium.

There’s no way around it—you’re going to pay more for ADBs up-front, but let’s apply the total cost of ownership (TCO) equation to the cost estimate. Gopi Krishnan, Meritor’s senior director, brakes for North America, explains that the TCO for ADB comes from: High reliability; Higher residual value; Increased uptime; Shorter CSA inspection times; and Relatively lower maintenance costs. Of course, the value proposition of ADBs can vary depending on vocation, application and the fleet manager’s priorities.

“Our estimates are that return on investments could be anywhere from 12 months to 18 months depending upon application, robustness of design of the brake, routes, etc.,” Krishnan explains.

With all this talk of ADBs, drum brakes are still a great brake choice, right?

Definitely. There’s a reason that drum brakes still make up more than 80% of the industry’s brake installations. There are plenty of excellent drum brake options in today’s market place. Take Webb Wheel’s brake drum offerings, for example. Webb offers a “good, better, best” drum selection depending on the fleet’s needs. It’s “best” selection is the Vortex Unlimited drum that promotes lower running temperatures with 25% longer life than traditional brake drums, according to the company.

Bendix, Meritor and Stemco all offer full drum brake product portfolios. Drum brakes are a tried and true product that is still a top choice among fleets in terms of safety and serviceability.

At the end of the day, the recent regulation changes relative to all types of brakes have the potential to significantly improve truck safety. However, Dan Dunkleberger, Haldex Brake Products Corp. product manager, explains the out-of-service rate for all brake-related violations are on the rise.

“Violations conducted during Brake Safety Week in was 16.2% compared to 13.5% in ; brake related violations represent around half of all vehicle out-of-service violations found by inspectors,” he explains. “Well functioning brakes should be our top priority, and effective brake maintenance is key to resolving this problem.”

Speaking of maintenance, what do I need to be aware of in terms of inspections and interval expectations?

Looking at cost-per-mile for brake intervals the same way as cost per mile for fuel will improve the overall expenses for a fleet. Regular periodic inspection schedules are the best way to monitor brake condition. Making sure all the technicians are trained and understand the setup and maintenance of the brake foundation is ongoing and forever changing.

“From a maintenance perspective, there’s a lot of give and take between [drum and air disc brakes],” says Dennis Griffin product manager, commercial vehicle friction, Federal-Mogul Motorparts. “With air disc brakes, if you only need to replace the pads, and not the rotors, then replacement is faster than it would be in a traditional shoe lining replacement. But if you need to pull the rotors, then you’re looking at removing the hub, cleaning and reinstalling the bearings and replacing the seal, which changes the equation entirely.”

The big brake maintenance challenge is maximizing the brake lining usage. When lining is measured during a PM, the maintenance manager must make the call to send the vehicle back on the road knowing that there is enough lining to make it to the next PM. Changing shoes too soon throws away usable lining, but sending the vehicle out with too little lining assures that a new drum will be required when the vehicle returns and safety is compromised.

“During a PM, along with lining thickness measurements, chamber strokes should be checked to make sure that auto slacks are functioning properly,” TMD Friction’s Thompson recommends. “Brake and slack adjuster maintenance manuals should be referred to for specs. Thorough inspections should be made of air lines, chamber bracket welds, bracket attachment to the spider and air chamber attachment to the chamber bracket. Any flaws found in the components should result in their replacement.”

S-cam drum brake friction is typically easy to inspect in terms of lining thickness on the vehicle. “Friction manufacturers incorporate lining wear indicating features, which make a visual inspection rather straight forward. In some [drum brake] cases dust shields may need to be removed to make an inspection,” Stemco’s Wieczorek explains. “Air disc brake (ADB) friction can be inspected by looking through the caliper-loading opening; however, some applications may require removal of the wheel to gain an accurate inspection.”

For drum brakes you’re looking for a .25-in. minimum thickness and for air disc brakes, a .12-in. minimum thickness. Regular periodic inspection schedules are the best way to monitor brake condition.

What is important to know about brake lining selection?

The No. 1 takeaway to remember is don’t skimp on the friction material. Make sure you get the correct lining for your application.

“Fleets, today, are under intense pressure to cut costs. In most cases, using the same friction material on both the tractor and trailer helped aid in this process,” Haldex’s Dunkleberger says. “This common sense practice was made cost prohibitive when RSD friction products were first introduced into the market. Higher acquisition cost accompanied with the abrasive compounds of most RSD friction suppliers caused fleets to carry two separate friction materials. This ‘forced change’ significantly increased brake costs and effected the brake balance that many end users worked so hard to achieve.”

To get the most for your money when purchasing friction material, you need to understand the difference between premium and economy brake linings and disc pads and premium drums and rotors. That is a challenge that is usually deferred to the trust of the local distributor or dealer.

“There is tremendous value in premium offerings that will be tapped as fleet knowledge increases,” TMD Friction’s Thompson says. “Linings and pads are available that can greatly increase brake life, depending on application. The more relines that can be avoided due to longer life, result in significant saving to the fleet, even though more money is paid up front for the wheel end kits.”

Spending more money up front for quality material can save at least one reline over the life of the vehicle.

While it’s easy to get excited about jaw dropping acceleration and massive towing power, let’s make one point clear:

Stopping is just as important as going.

To that end, we wanted to talk with a brake expert about everything from basic brake tech all the way to disc brake conversions for classic cars and towing upgrades for late model trucks. And we found the perfect guy for the job in Tom Reid. Not only is he president and CEO of a top-tier performance brake company, SSBC-USA, Tom’s also an engineer who grew up working with his uncle’s grassroots race team.

So yeah, he knows a thing or two about bringing fast vehicles down to a safe, controlled stop.

If you’re mulling over a brake upgrade or just don’t feel there’s enough “Whoa Nelly” under your right foot, then it’s worth checking out our full interview with Tom in the OnAllCylinders podcast section. But you can also read 10 short excerpts from the discussion below.

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10 Brake Tech Questions with Tom Reid from SSBC-USA

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1. What Are the Most Common Topics You Hear on Your Tech Line?

“Brakes seem to be the last thing folks think about, so most of the questions we get are panicked questions: ‘I just installed big tires and a lift kit, and now I can’t stop my truck—what do I do?’ (Laughs)

“It’s not really as much about the nuts-and-bolts of a brake kit. People almost treat it like a black box. They just know what they want to do—stop their vehicle better.

“And a lot of times, there’s a premium on what it looks like. Brakes have become an accessory for a lot of people spending big money on a restomod or show truck, and they’ve got those big wheels that open it up. People want custom colors—the aesthetic aspect now, is almost as important as the performance upgrade.”

2. What’s Often Overlooked About a Brake System?

“Let’s go back to an OEM brake. Manufacturers are designing that brake system to work for a huge bell curve of people—everyone from a teenager who’s heavy on the brake pedal to someone who’s going 35 mph in the left lane. That brake system has to cover all of those people.

“And it usually does a very nice job of that, at first. But the system is going to degrade from that point forward. So it was already kind of a stretch for some of these specialty applications. And once you get outside of that bell curve, the system’s not going to suit your needs.

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“Sometimes [when brakes are under-performing] it’s DIY’ers not doing a proper brake upgrade, some of the times it’s, if you’re taking an OEM brake system and replacing it with OEM parts, you’re not necessarily upgrading at all.

“So there are going to be issues until you upgrade.”

3. When You Replace Brake Pads, Should You Replace the Rotor Too?

“We absolutely recommend that you never replace pads without replacing the rotor too. Even if you’ve still got some life left in your rotor.

“That old pad and rotor have been bedded, they have been mated. Their flaws are now matched and interlocked.

“Even if you’ve got an upgraded pad, if you go and put that on an old rotor that’s been bedded to another pad, it’s not going to have the same surface area, it’s not going to have the same characteristics.

“And it’s not going to break-in properly—that’s the big thing. It all has to be done as a set, a system, and it all has to work together. And they often have to be broken-in at the same time.”

4. What Symptoms Predict That a Brake Upgrade is Necessary?

“When you start doing anything to these vehicles, the first thing you should look for is ‘Has the system changed? Did the pedal get softer?’ Is it making weird noises?’

“You can look at the pads and see if there’s excessive wear. We look for uneven wear, we look for gouges in the rotor—most wheel wells you can stick your head in and get a decent idea of what’s going on.

“Obviously there’s catastrophic failure. Brake fluid on the ground is never, ever a good sign.

“So there are a lot of little indicators, but the ultimate red flag is the vehicle’s not stopping as fast as you need it to stop anymore. That’s the one true indicator that something’s amiss.”

5. Is There a Specific Recipe or Brake Upgrade Progression That You Recommend?

“First, we determine two things: What the application will be, and second, how much you want to spend.

“You can do a cheap upgrade, you can get better pads and rotors. Those will make your existing system better, no matter what. But will it make it good enough?

“Take trucks for example. Guys are adding big wheels, 300 pound bumpers, a lift kit—you don’t have to be an expert to know that’s changed the physics of the vehicle.

“Your OEM brakes were sized for a completely different wheel and center of gravity. You hit the brakes on a lifted, 9,000 pound truck, instead of 75 percent of the weight shifting to the front, now 90 percent is going to the front. So that brake has got to do a lot more stopping.”

6. Should Truck Owners That Haul & Tow Consider a Brake Upgrade?

“We get a lot of folks that are pulling trailers, or have a daily work truck, so we recommend a caliper upgrade. It involves changing the physics of the system, because you can’t just take a stock OEM caliper and tweak it to perform better.

“You need a better braking system at the wheel. To us, that would involve larger, fixed calipers, better pads, and for us, we go with an OEM diameter rotor, for the whole reason that it’ll still fit in that OEM wheel.

“But it adds stopping force. We call that our B8 Barbarian kit.

7. What’s the Difference Between a Sliding & Fixed Caliper? Which is Better?

“On a sliding caliper, you have a cradle bracket that holds the pads, and you push on one side of that rotor. That’s the standard caliper that’s on almost every major vehicle, at least up front. Some still have drums on the back.

“Sliding calipers have a lot of travel and flex in them. So you’re not getting the maximum force between the caliper and the rotor, because you’ve got too much deflection. Too much travel and too much flex.

“In a fixed caliper, the only things that move are the pistons. But you’ve got a lot more caliper on the inside and the outside of that rotor.

“We also have to fight the urge to fit the biggest caliper we can, because there are other system parameters. Instead of two 64mm pistons we add six 64mm pistons, you just wouldn’t have enough booster, you wouldn’t have enough master cylinder.

“So we optimize the system by adding as much piston area as we can, which translates to force, and then we get the biggest pad that will fit on that rotor.

“That’s the best way to get greater stopping force. But again, it’s got to fit into the wheel.”

8. Does a Caliper Upgrade Swap Work with an Anti-Lock Brake System (ABS)?

“An upgrade, if done right, will work better with ABS than without. We do a ton of before/after testing, and we can see the difference in performance even in a really slippery situation.

“You’re really talking about two relationships here: the relationship between the tire and the road, and the relationship between the caliper and rotor.

“ABS is looking to pulse to stop. So if you’ve got the OEM sliding caliper, that piston has to travel twice as far—it not only has to push the inside pad against the rotor, it’s got to pull the cradle bracket in from the other side.

“And that all takes time. It doesn’t sound like a lot, but you’re talking about pulsing anywhere from 10 to 18 times a second with ABS.

“In a fixed caliper, you’ve got pistons on either side, so they travel half as far. So they will pulse faster, giving control back to the relationship between the tire and the pavement.”

9. Should You Address the Brakes on a Modified, Upgraded Classic Car or Truck?

“You’re going to be going a lot faster, who are you kidding. (Laughs) But you’ve got to assess where you are. Do you want to keep anything original, like the booster and master cylinder?

“We check to see what master cylinder and booster you’re going to use. Then we’ve got to make sure there are no changes to the knuckles or anything else. And will your wheels receive a larger caliper?

“So we have to work with the builder to see if will all work together.”

10. Do You Recommend Swapping Brake Drums for Discs on an Older Car or Truck?

“Is it better to upgrade from drums to discs? Yes, it is. Every time. The vehicle will stop better.

“But if you’ve got a classic car that’s only driven to weekend shows, a disc conversion is not always a good investment. If you’ll like the feel of your brakes and it’s working for you, that’s fine.

“The minute you expect better performance, cornering, you change suspension parts or go with bigger wheels, then that OE drum is probably not going to be sufficient. Especially in the front.”

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Tom wanted to give a special shout out to his pal Griff Jordan from PowerStop brakes for helping him prepare for this conversation.

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You can hear more from this interview in the OnAllCylinders Podcasts section.

And if you’ve got specific questions on your brake setup, Tom and his team of brake experts are ready to help. You can reach them via the Contact Us page at SSBC-USA.com to begin the conversation.

Heck, they may even let you talk to Bella.

Want more information on heavy duty truck brake lining? Feel free to contact us.