A mechanical expert has criticised the type of testing used by a company which is on trial after a triple fatal crash.
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A BP truck and trailer, which had been serviced by Heavy Mechanics, decoupled and hit two cars on the Wodonga-Yackandandah Road on August 7, 2014.
The trailer hit two cars.
William Kennedy, who had worked for the navy and assesses mechanic failures for the insurance industry, said pins linking trucks and trailers were "critical" components.
In evidence played in the Wodonga County Court on Thursday, he said the pin was critical as it was the only thing linking a trailer to a truck.
Heavy Mechanics director Keith Haire previously told the court the business would use tug tests to check the integrity of the link between trucks and trailers.
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The tests involve applying trailer brakes and rocking the truck back and forth to check for movement.
Mr Kennedy was critical of such a practice and said he didn't endorse it.
"Does it have any function in terms of assessing the wear on a tow eye coupling?" prosecutor Andrew Palmer QC asked.
"Absolutely not," Mr Kennedy replied.
Mr Palmer asked why not.
"Well, if you have a prime mover and a trailer which it's connected to, when you drive the trailer forward you have a pin here which is then under tension," Mr Kennedy aid.
"You can't measure the wear factor on a pin that's under tension.
"You must separate it."
Mr Kennedy said wear on components suggested a nut used to secure the system was insecure and the shaft moving.
The trial will continue on Friday.
