Tensions ran high during a coroner's inquest today as experts again clashed over why a piece of a truck came off and flew like a missile through a ute window, killing a young father inside almost 18 years ago.

Pukekohe plasterer John Edward "Eddie" Tavinor was decapitated when part of a driveshaft came through the windscreen of his ute as he drove in the northbound lanes of Auckland's Southern Motorway, between the Mt Wellington and Penrose off-ramps, on the morning of November 20, 2000.

Tavinor's partner, Michelle Foord, gave birth to their third child 10 days later.

In an inquest into Tavinor's death two years after, three expert witnesses agreed the driveshaft separated because of bearing failure, with wear and tear on a bearing "well in excess" of the manufacturer's limits and which should have been detectable during work on the vehicle at Roadlife Services 11 days before the failure.

Of the opinion that the original coronial finding was incorrect, engineers Peter Morgan and Timothy Smithson, of investigation firm Assesco, made a submission to Crown Law in 2013 asking for a new inquest, which was subsequently granted.

The second inquest got underway in November 2017, and has, nine months later, resumed today at the Auckland District Court.

Eddie Tavinor died instantly when a truck driveshaft's universal joint (pictured) hit his ute's windscreen. Photo / File

The coroner was quick to stress to the experts before him that the point of the hearing was not about blaming anyone but figuring out with a sense of finality why the incident happened, claiming Tavinor's life.

In giving evidence, Timothy Smithson explained his and Morgan's joint theory that two parts within the driveshaft clashed with each other, causing it to come off the vehicle.

He pointed to two police photographs and markings on the driveshaft shown to support his theory.

Smithson said two separate events, involving the gearbox and the driveshift, happened at the same time.

"The driveshaft is set at a certain angle to the gearbox," he said. "When those components are operating properly there's no issue, truck performs properly, but if one of the universal joints fails, it catastrophically fails."

During the cross-examination of Smithson, the coroner interrupted at least twice to tell the experts to stop arguing and for others to quieten down.

There were also disapproving looks from Michelle Foord and her family friend. Foord's son was also sitting with them.

Another expert, Bruce Currie, disputed the theory, saying the clash did not occur.

He pointed to a part of the universal joint in its assembled state with silver marks on it, saying that if a clash had happened, there would be clear corresponding marks but there were no such marks.

"The only conclusion I can draw from that is that these items did not come into contact."

Eric Stevens, an independent expert, said he did not believe the parts impacted to cause the driveshift to come away.

Christchurch-based engineer Shane Gooch added there was "no evidence of a causal clash".

The clashing force was in the wrong direction, he said.

Paul White said, again, he found no evidence that a clash happened and there was "no doubt" in his mind.

The inquest is scheduled to wrap up on Friday. 

A slip yoke mechanism for a heavy truck similar to that which killed Eddie Tavinor when it came free from a truck on Auckland's southern motorway in November 2000. Photo / File