An Adelaide trucking company boss has been convicted of manslaughter after faulty brakes killed one of his drivers.

Fifty-six-year-old Peter Francis Colbert, the owner of SA trucking firm Colbert Transport, has been jailed for 12 and a half years after the death of driver Robert Brimson in March last year.

Mr Brimson had to take quick action to avoid heavy traffic on Main South Road at Happy Valley in the seconds before his truck slammed into a pole.

Colbert was also convicted of endangering the life of another driver, Shane Bonham, when the brakes failed on the same truck two days before the fatal crash.

Justice David Peek said Colbert’s psychological report revealed him as a risk-taking, arrogant and narcissistic person, who was falsely self-confident about his own driving skills.

Justice Peek quoted from the psychological report.

“I can bet you though that 10 to 1 that I'd still be sitting here talking to you if I did drive the truck that day,” Colbert told the psychologist.

“I don't expect people to do what I can do with a truck.

“The truth is most of the blokes I deal with have no skill.

“To be honest I'm still trying to figure out why he [Mr Brimson] hit the post ... I wouldn't have gone near that.

“It's instinct, you've either got it or you don't.

“But he did save other lives so I can't knock the bloke.”

The court heard that the truck was in operation every day of the week, clocking up more than 800,000 kilometres by the time of Mr Brimson's death.Several people who appeared before the court insisted that Colbert was well aware of the truck’s faulty brakes, but that he said if anything happened it would be a fault of the driver.

Truck driver Dale Dahlhelm said in court that he could tell the brakes were poor after he spent a day in the truck.

“I could hear air hissing from the rear of the vehicle and it was pretty hard to pull up sometimes,” he said.

“When you put your foot on the brake, the vehicle wouldn't slow down in a hurry.

“If you needed to, you had to use the gears to slow down as well.”

Mr Dahlhelm said he got Colbert to look at it when he returned to the depot at Green Fields.

He said Colbert told him: “The vehicle's fine. It's all right.”

Mr Dahlhelm replied: “What about the air? It's not building up any air.”

Dahlhelm said Colbert jumped into the vehicle, revved it, and said “there's your air”.

“I said: ‘I'm still getting the air leak at the back of the vehicle’.”

Mr Brimson’s last moments were recorded by the truck’s dash board camera.

The judge read out his final words.

“Oh [expletive] brakes,” Mr Brimson said.

“Where am I gonna [expletive] go.

“I've got nowhere to [expletive] go.”