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Air disc or drum, spec and maintain

Bendix’s ADB22X Air Disc Brakes offer maximum stopping power, the virtual elimination of brake fade, and straight, stable stops.

Bendix Spicer Foundation Brake LLC regards brakes as the most fundamental vehicle safety system

By Gary Ganaway

The federal Compliance, Safety, Accountability (CSA) program that the Federal Motor Carrier Safety Administration (FMCSA) introduced in 2010 is reshaping the compliance and enforcement landscape. Phase I of the federal reduced stopping distance mandate went into effect in August 2011. The regulation, which prescribes shorter stopping distances for Class 8 tractors, spurred technological improvements in foundation brakes that benefit the entire commercial vehicle industry, including motorcoaches.

In May 2012 the National Highway Traffic Safety Administration (NHTSA) released a Notice of Proposed Rulemaking that would require full-stability technology, known as Electronic Stability Control (ESC), on truck tractors and certain buses with a gross vehicle weight rating greater than 26,000 pounds (11,793 kilograms).

The commercial vehicle industry, including the motorcoach segment, is changing rapidly. Amid this change operators remain under intense pressure to manage operating costs in the face of escalating costs. To do this they must field increasingly safe, efficient vehicles that bring maximum return on investment.

Key for operators is choosing braking systems whose performance, reliability and durability meet the challenges posed by these recent changes. Properly spec’ing and maintaining brakes is fundamental to success in the motorcoach segment.

Specs begin with needs
In spec’ing braking systems, motorcoach operators must make the important choice between foundation drum and air disc brakes while basing their decision on a deep understanding of the unique needs of their operations. Brake manufacturers and motorcoach OEMs then work together to design a brake package that meets those needs.

At Bendix we employ a team of engineers who work full time with OEMs to spec brakes. Together they take into account factors such as load, wheelbase, center of gravity, maximum speed and which type of tire best mates with the brake system. Engineers help to size brakes, chambers and the air system.

The two top priorities are brake balance and stopping distance. In a well-balanced system all the brakes on the vehicle operate at approximately the same temperature and wear at the same rate under normal operating conditions, resulting in best overall performance and longest life.

The new federal reduced stopping distance regulation does not include motorcoaches, whose requirement remains 280 feet at 60 mph. However, the mandate has led to significant developments in braking technologies that benefit the wider commercial vehicle industry.
Motorcoach operators can choose among the latest foundation drum and air disc brake designs. One development is larger and more powerful drum brakes, engineered to develop the increased torque necessary for shorter stops. The brakes then sustain that torque, reducing brake fade and stopping distances.

Even with the improvements to drum brake technology, however, air disc brakes still provide the best available performance and safety.

Air disc brakes offer an advantage
Lessons learned from prior technologies have enabled an evolution to the modern, effective designs that have overcome the shortcomings of both drum brakes and the early offerings of air disc brakes. Today’s air disc brakes offer maximum stopping power; the virtual elimination of brake fade with no degradation of stopping power; and straight, stable stops. Air disc brakes also provide longer brake life and faster pad replacement, simplifying service and improving uptime.

Another advantage is passenger car-like feel, which means less fatigue for motorcoach drivers traveling long distances. Concerning the stopping distance, the advantages of air disc brakes over drum brakes increase significantly as speeds rise above 60 mph. This is particularly relevant to motorcoaches where many states make it legal for them to run at higher speeds.

Fleets and other end-users are increasingly choosing air disc brakes over the more economical drum brakes. This rapidly growing customer base can attest that today’s air disc brake is an engineering achievement. It is quickly moving away from its roots as a brake for specialty and niche applications and emerging as a viable option for everyday use.

For motorcoach operators who transport men, women and children every day of the year, the superior performance advantages of air disc brakes are particularly compelling.

Two levels of inspection
The safe operation of a motorcoach begins with the brakes. In addition to stopping the vehicle, the foundation brakes are an integral element in many active safety systems like ESC full-stability technology. A malfunctioning foundation brake compromises the vehicle’s safe operation.

Properly maintained with the right parts, today’s air disc and foundation drum brakes are largely trouble free. At Bendix we recommend two levels of maintenance.

First is the regularly scheduled preventive maintenance inspection, often based on a set mileage interval like every 30,000 miles. The vehicle receives a thorough inspection. For drum brakes we recommend following the manufacturer’s instructions for any automatic slack adjuster installation and maintenance. Their setup procedure will differ because each manufacturer takes a different approach. The regular inspection also includes a check for lining wear.

The automatic adjuster built into air disc brakes, sealed and lubed for life, is a major advantage over drum brakes. While air disc brakes require very little maintenance, pad wear is a concern and requires routine inspection. Fortunately, pads on over-the-highway motorcoaches can last 300,000 to 500,000 miles depending on how aggressively the vehicle is driven. Pad replacement takes about 15 minutes per wheel-end once the wheel is off, compared to approximately an hour for drum brakes. Technicians should also check the rotors for cracks, which are rare, and rubber boots and seals to ensure they are intact. A check of parking capability is also important.

The second level of maintenance is the pre-trip inspection. During this walk around, drivers look for obvious problems like loose hoses and leaks. They should also check the disc brake rotors for cracks; an indication the brake is disabled or not operating properly. Drivers should check for lining wear on drum brakes, if it is possible to do so with the wheel on. We do not advise getting up under the vehicle for every pre-trip inspection but once or twice a week is a good idea.

Drivers should also heed warning lights and be watchful for brake system problems while driving. Most importantly, they need to be aware of brake pull — the feeling of the vehicle pulling to one side or the other during braking. The issue could be with the lining or an adjuster that is not working properly. At this point a technician should perform a complete brake system inspection.

The same is true any time a driver observes smoke. A wheel may be locking up or a brake is dragging. Though brakes have come a long way in terms of reliability, problems will still arise. If something doesn’t feel quite right, have it inspected. We cannot stress enough that the brakes are the most fundamental vehicle safety system.

Trust certified techs and OEM parts
Commercial vehicle brakes do not look much different than they did 30 years ago. From a technological standpoint, however, today’s braking system that brings a fully loaded modern motorcoach to a complete stop within the mandated distance represents a giant leap forward. These are not your father’s brakes.

The systems are both mechanical and electronic, with an electronic control unit (ECU) to direct the antilock brake system. Brakes will become more technically advanced as systems continue to evolve to meet increasingly stringent safety requirements. For that reason Bendix strongly advocates using certified technicians to service brakes. Federal regulations do not require certified technicians be used, but common sense does — once an operator understands how complex the systems are.

Equally important is maintaining the braking system as originally intended. Use original equipment replacement parts wherever possible, from automatic slack adjusters to lubricants. Deviating from original equipment to save money very often introduces problems. Operators find the parts do not perform like the original equipment. They pay more to resolve the problem than they would have for the original replacement part at the outset. An example is brake relining. We encourage the use of lining specified to meet the OEM requirements. Because of the reduced stopping distance mandate, the newest generation of brakes is more powerful than its predecessors. The brakes achieve this performance through design advancements and carefully chosen friction material. Incorrect or inferior replacement friction material can reduce performance, wear out sooner and negatively affect vehicle safety. BR

Gary Ganaway is director of marketing and global customer solutions for Bendix Spicer Foundation Brake LLC.

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Posted by on Aug 1 2012. Filed under Maintenance. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry

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