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NTSB Warns Against Manually Adjusting Slack Adjusters to Fix Truck Brake Problems

August 22, 2007

WASHINGTON, D.C. --- The National Transportation Safety Board has issued a warning about the dangers of manually adjusting slack adjusters as part of truck brake maintenance efforts. Automatic slack adjusters should not be manually adjusted after the initial installation adjustment, the NTSB said. Manually adjusting an automatic slack adjuster to correct an out-of-adjustment brake will not fix the underlying problem, and the brake will likely go out of adjustment again soon.When an automatic slack adjuster is out of adjustment, it indicates there is a problem with the adjuster, with the adjuster's installation, or with related foundation brake components, which manual adjustment will not fix, the NTSB said.In a 2003 accident in Glen Rock, Penn., a dump truck with out-of-adjustment brakes was unable to stop on a steep downgrade. The truck struck four cars, and one car struck three nearby children. Two people died as a result of the accident.Mechanics had repeatedly manually adjusted the dump truck's automatic slack adjusters. They did not look for underlying problems with the adjusters or related foundation brake components, so they misdiagnosed the brake problems. They were not properly educated on automatic slack adjusters and how they relate to foundation brake systems, the NTSB said. According to Federal Motor Carrier Safety Administration estimates, about 8 million registered commercial motor vehicles are equipped with air brakes. Many may be operated by drivers with no air brake training, who may be poorly informed about automatic slack adjusters. Even professional truck maintenance and repair organizations sometimes give out inaccurate or inadequate information on automatic slack adjusters.
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