Air Disc Brakes – Can't Live With Them, Can't Live Without Them

It's not exactly accurate to say that fleets can't live without air disc brakes. Many, if not most, fleet maintenance managers are getting along just fine without them. But that could all change by the end of the decade. The U.S. Department of Transportation (DOT) and the National Highway Traffic Safety Administration (NHTSA) have, for several years, been working on new standards that would require heavy truck stopping distances to be reduced by 30 percent. It's all part of the agencies' goal of reducing heavy truck-related fatalities by 50 percent by 2010, and although there is no requirement in the proposed standard for any specific new braking technology, odds are that air disc brakes will play a big part in the years to come. A very big part.

None of this would be an issue if the heavy truck industry could shake the bad memories of the air disc brakes that were brought to market in the 1980s. Back then air disc brakes were seen as the next big thing, but reliability and wear issues took their toll, and fleets retreated en masse to the less effective but proven technology of the S-cam air brake.

20 YEAR HISTORY
But it seems nobody told Ron Szapacs. Here he is, 20 years later, still running his 650 Class-8 tractors with Meritor air disc brakes on the steer axles, without any complaints. His fleet may already be close to meeting the proposed DOT/NHTSA stopping distance requirements, without changing a single spec'.

Szapacs is fleet equipment maintenance specialist, power vehicles, for Allentown, PA-based Air Products, Inc., one of the world's largest suppliers of gaseous materials for industry and transportation. When your fleet regularly hauls hazardous materials, and one of your regular runs is supplying fuel to the Space Shuttle, you'd better know a thing or two about what works and what doesn't, and Szapacs has a pretty good idea why air disc brakes fizzled in the ‘80s.

"Being a private fleet, we were able to control our tractors and trailers a little bit more precisely than some other fleets, especially the huge fleets that have all kinds of van trailers, thousands of them being sent all over the country," Szapacs says. "We paid specific attention to brake timing, and brake application pressure. So we made the tractors and trailers work together, and that is a very important function that needs to be addressed with air disc brakes."

Szapacs points out that an air disc brake doesn't have a return spring like an S-cam brake does. And because it takes between nine and 11 pounds of air pressure just to overcome the S-cam brake return spring, a driver who puts five pounds of pressure on the brakes will engage the air disc brakes while the S-cams are still being held back by the return spring.

To back up his case, Szapacs cites industry statistics showing that 60 to 70 percent of the brake applications a truck driver makes are 20 pounds or less. On every one of those brake applications, the disc brakes are doing much more work to. And so, "the disc brakes would just overheat and wear out, and create a lot of problems," Szapacs says.

MATCHING UNITS
To address this issue, Szapacs paired every air disc brake system with a seven and a half pound crack pressure valve on the trailer's brakes. Figuring in air line length and air loss, Szapacs estimates that the system easily reached the eight to 10 pound criteria for overcoming the S-cam return springs before engaging the air disc brakes, and so the steer, drive and trailer brakes all worked together in unison.

"I think other fleets understood that," Szapacs says, "but, you know, you can get a trailer with a zero pound crack pressure valve, or one and a half pounds or four and a half, or six and a half, and I think a lot of fleets never spec' that valve, so they weren't sure what they got."

For fleets to match all their units, they would have had to go through every trailer in the fleet, and for some companies that just wasn't an option. "Say, FedEx, they've got 85,000 trailers. How would you do that?" Szapacs asks. "It would just be impossible. We have 1,800 or 2,000 trailers, roughly, but we always looked at that and we spec'ed a certain valve, and that afforded us the opportunity to make that work.

"I'm not saying we didn't have problems," he goes on. "With the first systems we had slide pin bushing problems. They kept wearing out and getting real floppy." Complaints to the supplier resulted in better bushings and O-rings to keep the dust out, but Szapacs found that when the systems were tighter, the calipers would hang up on the slide pins.

"We laughed at ourselves for that," Szapacs recalls. "We should have kept our mouths shut!"

The only other problem Szapacs can recall is the time a new tractor cracked both rotors on the same drive axle in its first three weeks of service. Turned out the truck was mistakenly equipped with a seven and a half pound crack pressure valve on one of the drive axles, but a one and a half pound valve on the drive axle that lost both rotors.

"We put the seven and a half pound valve on it, and the truck went through its life without an issue," Szapacs says. "So you can see how fleets that had a vast variety of equipment would really be plagued with problems."

"GENERATION TWO"
Amazingly, Air Products' fleet rode on those early "Generation One" Meritor 1560 air disc brakes for nearly 15 years. "We used them on drive and steer axles up until 1998, and they didn't have the new model out yet, so the '98 tractors that we purchased all had S-cam brakes on them," Szapacs recalls. "We actually still could have ordered the Meritor 1560 brake, but I knew it was being discontinued. We were having problems getting rotors and so on for the units we had, so at that point I thought, ‘Why buy another order of trucks with the disc brake that's going away? We're having troubles getting it now.'

In the 1999 model year, Meritor's new DX 195 air disc brake for steer axles became available, and from that year on Szapacs has spec'ed the DX 195 on the steer axles for all his new Mack and Freightliner tractors.

The biggest difference between the old brakes and the new DX models, according to Szapacs, is the way the brake actually operates on the slide pins that allow the caliper to slide freely on the rotor.

"The pins are totally sealed and lubricated, and in the past there was nothing on them; the pins were exposed, kind of like they are on a passenger car," he says. "That worked okay for 100,000 miles, but after that is when you hit the issues.

"The new systems have no external moving parts," he continues. "The diaphragm housings are all bolted directly to the caliper, so the brake is pretty much more pervious to water."

When Meritor introduced the DX 225 for drive axles, Szapac considered returning to air disc brakes front and rear. But he found that he couldn't beat the brake performance and cost-per-mile he was getting with S-cams on the rear and the DX 195 on the steer axle, so that's what the fleet has stuck with.

Air disc brakes were once considered for Air Products' trailers as well, but the cost/benefit equation never added up for Szapacs. "We tested early on with the disc brakes on the trailer, and we had some rotor issues and pad life issues," he reports. "We didn't see any improvements that we felt would really counteract those negatives. So we haven't gone with them on the trailers at this point, but that's not to suggest that we wouldn't test some of the new systems."

ORIGINAL PADS & ROTORS
Is Air Products' configuration the ideal braking combination?

Szapacs pays more up-front for the air disc brakes, but his trucks have more stopping power and maintenance costs on the DX 195s are, he says, "virtually nonexistent." Most of the units easily go 500,000 miles with no pad replacements or relines, and no rotor issues. Air Products trades its tractors out at 600,000 miles, and it's not uncommon for those trucks to be sold with their original pads and rotors up front.

The additional weight of the air disc brake units hasn't been an issue for Szapacs, because the extra pounds are limited to the steer axle. "There is a slight penalty, but you can afford another 40 pounds up on the steer axle, because it's so hard to get 12,000 pounds on the steer axle," he explains. "You know, you get 11,600 to 11,800 pounds, so what is 40 pounds more? You have 11,840. If you doubled that and you had an extra 80 pounds on the tandem drives, yeah, you'd have an issue there."

The higher purchase price is also a non-issue. The first round of purchases in the 1980s was partially subsidized by the manufacturer, but now that the units have been part of the fleet's standard spec' for 20 years, the cost is all but invisible. Says Szapacs: "It's there, but it isn't."

Of course, the most important issue is performance, and on that score the air disc brakes have proven themselves over and over for two decades.

"With the product we haul, we really promote safety," says Szapacs. "We have an excellent safety group and an excellent safety record, and that's one of the reasons we went to the air disc brakes. We felt that the cam brakes were really outdated; they were developed right after they came out with pneumatic tires, I believe! I mean, they've been perfected, and they've really improved the performance of it, but the disc brake does afford a much shorter stopping distance."

Although Szapacs has never measured the improvement in stopping distances, his drivers can tell the difference between air disc brakes and S-cams. In fact, when the drivers were first getting used to the increased stopping power, they would run right up to offramps at full speed, because they knew they could stop safely in a shorter distance!

"We weren't expecting that," Szapacs admits. "But they got to rely on the system, they knew it would really work, you didn't have fade, so those were some of the results that maybe weren't most desirable. Our driver trainers worked with all the drivers, and now, especially with air disc brakes only on the steer axles, they do notice there is still a much shorter stopping distance than with cam brakes all the way around."

PARTS SCARCITY
If there is any real glitch to the system, it is the availability of the spec'ed components and of replacement parts. There have been times when Szapacs has found himself reluctantly playing the role of the chicken in a "chicken-and-egg" situation. OEMs are reluctant to equip trucks with air disc brakes until there is adequate demand, but customers are reluctant to demand air disc brakes as long as they know that availability—and, thus, product support—is lacking (see sidebar, above). Those memories of the 1980s still linger, and there are few fleets willing to take a chance.

But Szapacs has never been reluctant to ask his truck suppliers to equip his units with air discs, and all of them—from White in the 1980s to Mack in the 1990s to Freightliner in the ‘00s—have come through, after some insistent nudging.

Parts, however, can be a different story.

"Believe it or not, we have had some instances where we've had problems getting brake pads, because we don't really use them," Szapacs admits. "Mack didn't put them in their parts inventory because we didn't request them, because if everything worked right, they'd run off the life of the vehicle.

"It sounds crazy, but that actually happened to us," he says. "We had a truck that got a stone wedged between the head and the caliper, and it damaged the rotor and the pad. This happened in Arizona, and we could get a rotor but we couldn't get a pad! We had some pads stocked at some of our locations, so we over-nighted some out. But we couldn't get them through the OE, because they didn't stock them; there was no need for them."

GET READY
As other fleets wonder how they might meet the proposed DOT/NHTSA stopping distance standards, Air Products is already looking ahead to the next generation of air disc brakes. To avoid 2007 engines, Szapacs is virtually doubling his normal new truck orders (from 80 to around 150) both this year and next, and he wants to make sure that next year's order includes the next generation of air disc brakes.

How will you stop your trucks with a 30 percent shorter stopping distance? If you follow the lead of Ron Szapacs, you may surprise yourself one day, when you realize you "can't live without" air disc brakes.

The Have-Nots
For every Air Products that has procured air disc brakes for their tractors, there's a Haas Carriage, that has tried and failed to equip its fleet with these rare brake components.

"We've been interested in them for years and years," says Terry Hass, president of the Louisville, KY-area cabinetry hauler. "Last year was the first time I sent out my basic spec's. On my options list I put air disc brakes on, and I sent it out to four vendors, that I recall. They weren't available with any of them.

"I think it's lack of demand," Haas says. "I've read some of these surveys, and near as I can tell it's lack of demand."

Even though the company doesn't haul dangerous loads, safety is a big reason Haas wants air disc brakes. "We think they'll stop quicker and last longer—those are the two main things," he says. "The safety factor plays into this a lot, because if it shortens the stopping distance, it can save a crash, or even a life."

He also sees a significant maintenance benefit from using air disc brakes, because the pads are so much easier to change than drums, and because it's easier to visually inspect pads.

With only 32 tractors in the fleet, Hass Carriage doesn't have the same kind of clout with OEMs a larger fleet would. Instead, Haas is relying on persistence. Every year, he attends major truck shows, and every year he spends time talking with air disc brake suppliers. "We live just across the river from the Mid-America Truck Show and we see all the major vendors who display there. They're trying to get us to put pressure on the truck OEMs, so they can get them, I do believe."

Haas believes that's a good strategy, and he hopes it might pay off by next spring, when he'll be ordering four to six new tractors and six to 10 new dry van trailers. Although he splits his purchasing between several OEMs, all it will take is for one supplier to say, "Yes, we can get those for you" for Haas to be happy.

"If somebody offers air disc brakes, we'll favor them over someone who doesn't," Haas says. "If one guy has air disc brakes and they're reasonably priced, we'll probably go that way."

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