Ask around. You won’t have a hard time finding someone who remembers an earlier generation of air disc brakes. The technology was ahead of its time, it seems. They worked well, but they didn’t last very long. Rotors cracked apart in months, pads wouldn’t go much beyond 15,000 miles, and mixing aggressive discs and less aggressive S-cams on a combination unit created its share of excitement.

Modern ABS has mooted the latter issue, and extensive redesigns and improvements in metallurgy and materials formulation have resolved the former. Designs, performance, weight, and cost have all improved markedly, and some of Canada’s largest and most successful fleets are now taking cautious second looks at air discs. They seem to like what they’re seeing.

Trimac Transportation of Calgary is one such fleet. It began testing air discs four years ago in a high-duty-cycle operation running 120,000-lb GVW B-train coal-haulers in the Black Hills of western South Dakota. They put a half dozen power units into service with air discs at all six wheel positions to test against their S-cam equipped cousins.

Bill Januszewski, Trimac’s director of purchasing and equipment technical services, says the S-cam-equipped trucks saw 100,000 to 125,000 miles between relines, while the air-disc equipped tractors went out beyond 325,000 miles on the same pads and rotors.

“The first group of trucks we tested is now at the end of their life cycle, and we have had virtually no problems with them,” Januszewski says. “The original rotors are still running in all the trucks, and I think we replaced one set of pads over several hundred thousand miles. We pretty well tripled the life of the brakes on those units compared to the [S-cam equipped] trucks in the same service.”

Because Januszewski remembers the first go-around with air discs, the company is still testing here in Canada. Because of the higher gross and axle weights in Canada, Trimac wants to be “very sure” air disc brakes are the right choice for our operating conditions as well. “We’re not yet seeing the pad life [in certain high GVW applications] we saw in the South Dakota fleet, but we’re not far off,” he says.

The view from behind is a little different
when a trailer has air disc brakes.

The Trailer Market:

While air discs have become the standard tractor spec in its U.S. fleet, Trimac is moving ahead slowly with trailers. It’s running less than 100 air-disc equipped trailers at this point.

Winnipeg-based international truckload carrier TransX is another story. It has more than 500 air-disc-brake-equipped trailers on the road already.
“We jumped right in, both feet,” says Brian Hiebert, vice president of equipment maintenance at TransX. “Every trailer we buy from today forward will have disc brakes. And we haven’t bought a trailer in the last year-and-a-half that didn’t have them.”

Rob Sims of SLH Transport of Kingston Ont. is looking too, though somewhat more cautiously. He saw the potential for improvements in stopping distance with less brake fade, and potentially lower maintenance costs, and so began testing disc brakes on a select group of B-train vans operating in western Canada.

“In late 2006, SLH built two identical groups of B-trains — except that one had traditional S-cam brakes and the other had air disc brakes — so the two could be compared,” says Ray Camball, fleet sales manager at Trailmobile Canada in Mississauga.

Money Ahead In the Long Run:

There aren’t many downsides to air discs, but weight and cost are two of the perceived drawbacks. They’re more expensive from the get go, but how do they compare when you factor reduced maintenance and downtime costs? In other words, how does the lifecycle cost compare to S-cams?

“The acquisition costs are significantly higher, there’s zero doubt about that, but prices are improving as production ramps up,” Januszewski observes. “Having said that, I have absolutely no doubt that
the life-cycle cost of air disc brakes will be lower.”

While discs are gaining popularity, truck OEMs are
still a bit vary about them on wide base single tires.

Januszewski found the South Dakota air discs outlived the S-cams by a three-to-one margin — and that was in a severe-duty application. TransX’s Hiebert says he expects brake jobs will be two-to-one over S-cams, and probably better, so he’ll cut his maintenances costs at least in half over the eight-to-10-year lifespan of his trailers.

Trailmobile’s Camball points out that while the initial cost is higher for disc brakes, in a case where premium options are spec’d on drum-brake vans — such as auto-greasers for cams, slacks, and clevis pins — that cost disappears. Those system aren’t needed with disc brakes.

“It is still early for an accurate comparison on long-term maintenance costs and performance of the vans, but so far the results are encouraging. Drivers like them, and we have seen a slight reduction in maintenance related downtime,” observed Rob Sims. “I’m tracking and comparing the frequency, type, and cost of the work done on the brakes for the two groups. If the discs continue to run as well as they started off, the longer term savings may well offset much of the initial upcharge.”

Steel-hubbed air discs can add weight to a tractor, notes Januszewski. “Four hundred pounds heavier for a tractor with air discs at all six wheel ends,” he notes. “Go to aluminum hubs, and you’re only one hundred pounds heavier.”

That could be an issue in weight-sensitive applications, so could the upcharge for aluminum hubs. But Januszewski also notes that costs have been dropping steadily since he began testing for years ago. “I’m sure they’ll become more competitive as production increases and the brake makers get economies of scale on their side.”

But all three fleets told us that there’s one element to air discs that you just can’t hang a price tag on: performance.

You can get surprisingly good performance out of an S-cam brake with the extra wide blocks on the non-steer positions and using the 16.5-by-5-in. linings on the steer axles, notes Januszewski. “But you get it only once.”

“S-cam performance diminishes as the brake drums heat up,” he says. “I’m not saying there’s anything inherently unsafe about S-cam brakes — we have a whole whack of them in our fleet right now — but I am saying that the air disc brake is superior under repeated applications. The hotter it gets, the better it works. If you’re in a place like Colorado or British Columbia, better brakes are worth their weight in gold.”

For more on this topic, click below on “TRUCK TALK” for Jim Park’s audio program, “IS IT TIME TO SAY SO LONG TO S-CAM BRAKES?”