HEADLINES
Late ‘Braking’ News: Automatic Slack Adjustment Need Not Apply
Whenever there is a school bus crash,
one of the first things investigators look at is the bus’ brake system. A 2003 accident in Glen Rock, Pa., involving a 1995 Ford dump truck and four passenger cars, resulting in two fatalities, prompted the NTSB to issue a warning regarding automatic slack adjusters (ASAs), concluding that manually adjusting them is dangerous. Te board’s 2006 report on the Glen Rock
accident said the probable cause was an air brake-equipped vehicle with inadequately maintained brakes. Te culprit: the truck’s rear ASAs, which had worn quick-connect clevises and clevis pins that prevented the ASA from providing the correct amount of clearance or “slack” needed to provide the adequate amount of braking force. Te driver of the vehicle, who was also a
mechanic, had manually adjusted the ASAs. Manual adjustment “fails to address the true reason why the brakes are not maintaining adjustment, giving the operator a false sense of security about the effectiveness of the brakes, which are likely to go out of adjustment again soon,” the NTSB said.
VISUAL INSPECTION, PROPER KNOWLEDGE ON AIR BRAKES KEY All newly manufactured vehicles with air-brakes since Oct. 20, 1994 are required
to have ASAs, per FMVSS 121, Title 49, Part 571.121, Section 5.1.8. Many school buses today are equipped with air brake systems with ASAs. Properly trained school bus technicians know not to manually adjust ASAs, however, there could be some out there who may still do this due to lack of knowledge and out of habit. Tere was a time before ASA regulations
when it was necessary and recommended for drivers to manually adjust their brakes on a
regular basis. Once ASAs were
introduced, this was no longer needed. “ASAs automatically maintain the
optimum clearance between the linings and drums and do not need to be adjusted after they are installed,” said Mark Kromer, engineering manager for specialty products at Bendix Spicer Foundation Brake. Scott Corbett, director
service and warranty at Haldex Brakes Products Corporation, added:
of technical “Excessive
de-adjustment will cause brake adjuster internal components to wear prematurely and shorten the service life. Adjusting also can disguise hidden problems within the foundation brake assembly.” Manually adjusting automatic slack
adjusters should be done only for an emergency move to a repair facility or during the installation of new ASAs. Alan
Blue Bird Dealers Now Stock Performance Friction
Aftermarket Brake Products For those who operate and maintain Blue Bird school buses, being able to purchase
aftermarket brake products just got easier. Tanks to a partnership between the school bus manufacturer and Performance Friction, fleet managers can now purchase from their Blue Bird dealer Performance Friction Carbon Metallic brake pads and zero failure rotors for fleet applications. Tis also includes light and medium-duty hydraulic pads and rotors, as well as heavy-duty air disc applications for all makes of aftermarket school bus applications. Don Nichols, vice president of Blue Bird Aftermarket Parts, said the partnership
is a win-win for the customers the company serves. “Tis alliance will provide Blue Bird customers with top-notch quality and value, which will assist in keeping Blue Bird buses operating with the greatest up-time, at superior performance levels.”
32 School Transportation News Magazine March 2012
Fidler, a bus technician from Tippecanoe (Ind.) School Corporation, said the only times he manually adjusts ASAs is when he initially backs off the ASA during a brake replacement and after reassembly, per the manufacturer’s instructions. It’s a different practice during a PM service or a general inspection of the brakes. “A technician will first measure the brake
rod travel to determine if it is within specs. If they are not, he will then check to verify that the installation and initial setup was correct,” said Fidler, who is also the 2011 NAPT America’s Best National School Bus Tech Technician winner. “If this is OK, then the technician conducts a visual inspection of the components to verify no worn parts.” Kromer, Corbett and Fidler all stressed the
importance of visual inspections of ASAs by technicians, and bus drivers during their pre-trip inspection. Technicians should also know the ins and outs of air brake systems. Haldex, Bendix and other manufacturers all offer full air system training throughout the United States on a regular basis. “Most ASAs on the market require the full
return to ‘zero’ stroke to properly function, and if other wheel end elements are not in proper condition, replacing the ASA may not resolve the issue and the wheel end could go out of adjustment again,” said Kromer. “Tis is why it is critical that technicians have a full understanding of the whole air system, including its wheel end components, to ensure maximum vehicle safety.” ■
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