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Manually adjusted auto slack adjusters dangerous: NTSB

By Today's Trucking
Posted Mar 24th 2008 3:37AM

WASHINGTON -- It took a spectacular fatality for the U.S. National Transportation Safety Board to recognize the dangers in performing too-frequent adjustments to automatic brake adjusters (ABA).

In April 2003, a dump truck was traveling on a steep downgrade in Glen Rock, Penn. when the driver found he was unable to stop the truck. The truck struck four passenger cars, one of which struck three children who were on a nearby sidewalk. A driver and an 11-year-old child from one of the passenger cars were killed.

An investigation revealed that mechanics that worked on the truck had repeatedly manually adjusted the ABAs instead of looking for underlying problems with the slack adjusters or other brake components.

In a recent report, NTSB Acting Chairman Mark Rosenker warned, "manually adjusting automatic slack adjusters is dangerous. It should not be done, except during installation or in an emergency to move the vehicle to a repair facility."

The report emphasized that "manual adjustment of automatic brake adjusters (ABA) masks the real reason why the brakes are not maintaining adjustment, giving the driver a false sense of security about the effectiveness of the brakes, which will likely go out of adjustment again soon.

Frequent manual adjustments also cause abnormal wear to the internal adjusting mechanism for most automatic slack adjusters, which may lead to failure of this brake component."

A full accident report may be found on the Board's Web site, www.ntsb.gov, under Publications, Highway.

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