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The history of air disc brake usage on commercial vehicles


Updated 17-July-2018 by Walter E Frankiewicz

The history of air disc brake usage on commercial vehicles has it’s beginning in Europe.  Although air disc brakes were evaluated and developed in the early 1980’s for North American vehicles, the performance and durability problems at the time outweighed the benefits and those early evaluations were soon abandoned by the market.  In contrast, as early as twenty years ago, air disc brakes were widely used throughout Europe for all wheel positions.  Haldex has been a significant supplier of air disc brakes to this established market producing more than 1.7 million trailer air disc brakes.

In the mid 90´s a technology shift took place in EU on brake systems. Driven by the truck market, and Daimler in particular, an Electronic Brake System (EBS) replaced the former Anti-Lock Brake System (ABS). At the same time wheel-end technology shifted from drum brake to disc brakes (ADB). The driving forces for these changes were mainly improved braking performance utilized by better control of brake forces (EBS) and a more stable braking performance over the wheel end temperature range and lower hysteresis (ADB). Over a time period of about five years the EU truck and trailer industry shifted from ABS w/drum to EBS w/ADB and in early 2000 approximately 70% of the market had adopted these new technologies.

Of course, the European trucking industry and its supplier base are much different than North America and those differences allowed the easy adoption of air disc brake technology.  One of the significant differences was that many tractor/trailer combinations in Europe were truly combinations – staying together as a unit. Where in North America there are some vocations where this is mostly true (tankers), the high population vocation of hauling general freight over-the-road rarely has a “married” tractor with a specific trailer.  This is a contributing factor to why tanker fleets were the first Class 8 segment targeted in North America for adoption of ADB by the manufacturers of these components. 

Another key factor in the quick adoption of air disc brakes in Europe was the fact that each truck manufacturer designed and produced variants of their own drum brake – unlike the North American market where only a few manufacturers of drum brakes competed – Meritor and Dana for example.  The lack of standardized brakes for tractors in Europe tended to result in a higher component cost for the drum brake and associated hardware.  Therefore, the jump to the more expensive air disc brake was not perceived to be as great a hurdle, as it has been, until recently in the U.S. market.

Not until the Federal Motor Vehicle Safety Standards rules were changed decreasing the stopping distances required for Class 8 trucks (2011 and 2013) did North American fleets of all types take a real interest in moving to air disc brakes, or at least considering it. While many could certainly meet the new rules staying with drum brakes, forward thinking and safety-minded fleets saw an opportunity and started investigating the potential for their fleets.  Many of those fleets who preferred to stay with drum brake technology did see the need to boost their performance with wider brake shoes and more aggressive lining material, in addition to the OEM specified larger diameter steer axle drum brakes.  The added cost for these enhancements had the effect of reducing the gap between air disc brake and drum brake further.  Additionally, the un-foreseen noise, performance and durability issues that were induced by these more aggressive drum brake linings are only now surfacing. 

The advantages of air disc brake technology over drum brakes were fairly apparent even to those not yet ready to adopt them:  shorter stopping distances; less maintenance costs because of significantly quicker pad change versus a shoe change as well as fewer parts; weight savings for fuel economy and extra payload; no brake fade as experienced with drum brakes in high temperature conditions; similar deceleration effect and reaction time to familiar car technology, etc.  But, the disadvantages were also apparent – most notably the cost which certainly was impacted by the small quantity being made and sold, but also the simple fact that “we’ve always run drum brakes” so service and maintenance technicians know how to work on them and parts are readily available from any distributor, any place in the country. Additionally, there were alleged issues of brake imbalance if one unit of tractor/trailer combination has disc brakes and the other (probably the trailer) had drum brakes.  This notion has mostly been debunked as more competitors have entered the market, but the idea certainly had many fleets backing off any decision to change to air disc brakes. OEM’s didn’t help the situation by making it either difficult or impossible to spec air disc brakes on their vehicles….so even if a fleet was convinced they were best for their operation actually getting them on a new vehicle was a real challenge.

The increased standardization of ADB on many OEM tractors will push more disc brakes onto the trailers they operate with.  For some fleets with large trailer to tractor ratio, the payback to buy new trailers with air disc brakes may not make much sense, especially if most of the trailers they have in operation still have drum brakes because of the amount of time they keep them.  But fleets with a more controlled trailer population either throughout the fleet or for specific routes/customers and new tractors that came standard with air disc brakes will more than likely buy new trailers with them too.

Fleets today are looking for any way they can get a leg up in recruiting and retaining good drivers and having vehicles equipped air disc brakes sends a message that they are serious about their safety.  There is also an argument to be made that the pedal feel of a truck with air disc brakes is similar to that of a passenger car might open up the driver pool similar to how automated transmissions drew more people to the vocation.  Fleets are acknowledging that the improved safety performance of an air disc brake is undeniable.  The industry expects the need to recruit upwards of 80,000 new drivers a year just to replace retiring baby-boomers.  One suggestion being floated to do that is to lower the age requirement for interstate OTR CDL’s to 18 from the current 21.  Having ADB-equipped vehicles to put them in would probably be a good idea!  

With freight demand high and capacity very tight, in addition to drivers being particularly important, the less downtime experienced, the more freight can be hauled in a cost effective manner and more money to be made. 

Brakes, primarily the drum variety, have always been one of the top three violations found during roadside inspections with citations being issued and vehicles being put out of service.  A fleet will consider the fact that with air disc brakes that won’t happen resulting in more up-time.

Fleets that have done their homework on air disc brakes view the advantages as worth the extra upfront cost which is decreasing from the exorbitant initial premium price.  Haldex, has an easy to use / very accurate payback calculator on our website for fleets to compute their own payback for the ADB investment using their own profile based on cost expected at time of purchase.

In addition to current advantages of air disc brakes for trucking fleets of more uptime (less service hours and fewer out of service penalties), a safer fleet with satisfied drivers (shorter stopping distance, better pedal feel, more responsive, less prone to skidding) and lower overall cost; as the volume of air disc brakes made and sold in North America inevitably increases there will be more reason for fleets to spec them:

  1. Industry prices have come down significantly in the recent year
  2. The true price difference between a fully-functional drum brake and the air disc brake will further drive the cost advantages towards the air disc brake
  3. Technical expertise in working on air disc brakes will increase at fleets as well as outside service providers as training is integrated into the brake system training modules by Haldex and other suppliers
  4. The fewer parts that are required for air disc brake service (vs. drum brake service) are much more widely available
  5. The widely available service parts supplied by Haldex (brake pads and service kits) for air disc brakes are available through the U.S. and Canadian distribution networks – further simplifying the ease of service
  6. The retrofit-capable Haldex air disc brake will ease service and aftermarket choices while opening up the expensive and hard-to-get original equipment air disc brakes supplied to date.
  7. There are more competitors supplying air disc brake in the North American market today than there were even two years ago.  Fleet choice and price are becoming more optimal for ADB selection.

The Haldex ModulT air disc brake combines the company’s experience in the established European market with a design specific for the North American market.  It’s the lightest 22.5 trailer brake in the market optimizing lower weight with strength and durability.  It has fewer components than previous models with a single piston caliper mechanism delivering twin-piston like performance.  The unique design has only two slide pins and a completely closed caliper.  All disc brakes are easier to service than drum brakes but the Haldex ModulT goes one step further to simplify brake pad replacement by utilizing a boltless, snap on brake pad retainer.  Less service time equals more uptime, less cost and more opportunities to generate revenue.

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