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What's Stopping You? The 4-1-1 on Air-Disc Brakes

TORONTO  Do we really need air disc brakes (ADB) in Canada when traditional drum brakes seem to be good enough?

Since the latest generation of ADBs re-emerged in North America more than a decade ago, uptake by long-haul fleets has been paltry 10 percent or so. Despite the acknowledged technical superiority and performance advantages of ADBs, fleets seem happy with the devil they know. And why not; drum brakes work, we're familiar with them, they meet all the regulatory requirements and they can be repaired anywhere.

Still you have to wonder if Europeans know something we don't.

The ratio of drum brakes to disc brakes in European Union nations is practically the opposite. All on-road commercial vehicles in the EU are now fitted with ADBs. Some off-road trucks, such as mining and construction still use drum brakes, along with some military vehicles. Drum brakes comprise about 18 percent of total EU brake demand.

Why, then, have North Americans not embraced air disc brakes?

Chad Mitts, Meritor's general manager for North American Brakes says there are several reasons why North American fleets lag behind the Europeans in ADB uptake:

  • In Europe, the OEs decide what the truck is going to look like. North American truck makers build the truck the customer wants; in Europe, fleets get what the manufacturers build.
  • Different service infrastructure: Most European trucks are serviced at dealers with factory-trained technicians. Here, trucks are serviced by fleet technicians, jobbers, dealers, etc., which makes adoption of new technology more difficult. You have to deal with new parts and new procedures, and there are technician-training issues to overcome.
  • Our longer conventional trucks are dynamically different from the short-wheelbase EU cab-over-engine trucks. A typical North American conventional has a completely different distribution of brake work in a hard stop. The benefits of ADB are still there with our conventional tractors, but they are not as pronounced as on a shorter wheelbase COE models.
  • North American fleets are very cost-sensitive, and as long as low-cost options exist, they usually get the nod.

Air-Disc Drivers

When discussions first began of revising the federal stopping-distance requirements for trucks -- introduced in 2011 -- many assumed that would be the tipping point for air-disc brakes. Brake system manufacturers, instead, came up with advanced drum brake systems with larger friction surfaces. They easily met the new standard and effectively took the wind out of the ADB sails, but that was what fleets had asked for.

That advanced drum brakes meet the new stopping-distance requirements is only part of the story. Brake performance is proven on a test track with cool brakes under carefully controlled conditions.

"The distance requirements brake manufacturers had to meet with the new requirements are not real-world conditions," says Gary Ganaway, director of Marketing & Global Customer Solutions for Bendix Spicer Foundation Brake LLC. "They are a requirement the truck has to meet one time. In the real world with trucks coming off hills and all conditions being generally less precisely controlled, air-discs will out-perform drums every time."

Ganaway says there's a growing acceptance that the discussion doesn't begin and end with the stopping-distance requirements.

"Even with the price premium [of about a $1,000 per axle, give or take], we are still growing that segment of our business pretty dramatically," he points out. "It's simply because once a customer or their drivers experience disc brakes, it's very difficult to go back to drum brakes."

Ganaway says cost is obviously a factor, but perhaps less so where a safety and compliance are genuine concerns.

"If cost was equal, we'd never sell another drum brake," he says. "It's one thing to look at the price of something and assume what its value is, so we have put a lot of effort into getting the customer into the truck to experience the performance benefits."

Christopher Trajkovski, ‎vice-president of Fleet Maintenance at Winnipeg's Bison Transport says the intangible costs are ones less frequently considered.

"You can do ROI calculations on air-discs and build a good case, but it upsets me that there's incredible advantage to the performance of air discs that's not always considered," he says. "At Bison, we feel we have a responsibility to the motoring public to do the right thing, and all the data I have seen supports air-discs on the safety front."

And drum brakes remain our Achilles' heel when it comes to roadside inspections. Brake problems are typically the top-five out-of-service items, Mitts says. Even with automatic brake adjusters, roughly 15 to 20 percent of trucks are sidelined each year during the Commercial Vehicle Safety Alliance's (CVSA) Road Check and Operation Air Brake events. Similar numbers are reported at numerous inspection blitzes that take place throughout the year.

Brake adjustment issues are easily detected in routine inspections, if they are done properly, but Mitts says the industry really needs to move away from the practice of simply readjusting brakes with excessive push-rod travel. As any brake manufacturer will tell you, if an automatic brake adjuster is out of adjustment, it's probably a symptom of some problem with foundation brake, not a problem with the slack adjuster.

That problem virtually disappears with ADBs. That's not to say they are bulletproof, but roadside inspectors do not yet have a national standard for putting disc brakes out-of-service for improper adjustment.

Are Disc Brakes Too Good?

For every action, there's an equal and opposite reaction. In trucking that's sometimes referred to as the law of unintended consequences. In this case, we're talking about panic stops that send freight flying through the front wall of the trailer. The owner of a very prominent Canadian fleet tells Today's Trucking he has had such a problem, and he knows of a few others that have had similar difficulties tangentially related to the superior performance of air disc brakes.

"The disc brakes are not the problem," he says, "but what happens to the cargo when it's subjected to greater forward G-force that was the case with drum brakes."

He describes the stopping power of ADBs as "unbelievable," especially on LCVs with discs at every wheel position. He notes in a hard braking incident the initial G-force can be surprisingly high compared to drum-brake-equipped trucks, doubly so if that drum-braked truck was operating at the margins of its stroke length.

"We experienced situations where the load moved and the front end of the trailer was damaged following heavy braking," he says. "I have had these problems with some of my trailers and I have seen competitor's hauling particle board in vans, for example, where the entire load when through the front end. It's not the fault of the disc brakes; it's the way the vans were loaded. Not enough blocking was used in the van."

The owner of this prominent Canadian fleet says he is ordering disc brakes now at all wheel positions on most equipment, and he's closely examining his cargo securement methods as well as his trailer suppliers' construction methods.

"The problem is really with cargo securement in vans," he stresses, "not with the increased braking capacity." At the same time, he cautions that when you change one part of the equation, users had better be prepared to look down the line for unintended consequences. "We had to make some changes to our equipment and our loading practices. We haven't had any problems since."

Email Editor

In regards to freight moving forward, perhaps more emphasis on Defensive Driving for drivers would be beneficial. Better following distance and eye-lead time will prevent most hard stops. It amazes me how a lot of drivers like to ride right up on the back of other vehicles. This is dangerous and can be easily avoided.

I have been watching this topic for several years with the thought to change to discs for the superior performnce,. The shop that I contract my maintenance to (Independent garage) tells me a number of his customers have tried them with less than stellar results. I don't know if it has to do with the hills in BC, but disc warping is apparently a problem with the resultant brake pulsing which drivers dislike.