The boys said Mr Tobeck was not wearing a seatbelt and was lying face down. Liam reached through the open window and grabbed him.
"The water was just below neck deep. I held his head up first and shook him. He didn't look too good, his eyes had rolled into the back of his head."
The boys wrenched open the door, pulled out Mr Tobeck and dragged him onto the bank.
"We both had to open the door. The truck was blocking the path of the water flow," said Liam.
"I went and checked to see if there was anyone else in the back seat."
As Mr Tobeck lay on the bank he wasn't breathing.
"I was trying to snap him out of it," said Angus. "I smacked him on the cheek and kept talking to him. But he was making this weird breathing rhythm that didn't sound too good."
Liam said he knocked at a nearby house and asked the woman who answered to call an ambulance.
"She called the ambulance and I went back. I stopped a car and a man got out and helped me. [Mr Tobeck] was starting to moan by that stage."
Police, fire and ambulance staff arrived soon after and Mr Tobeck was taken to Christchurch Hospital.
Senior Constable Jim Manning said the boys deserved a bravery award.
"They didn't worry about getting someone else, they just dived in. And they went back in to see if someone else was in the vehicle, because that's what they were worried about. It's pretty impressive stuff. They saved his life. If they hadn't dived in and got him out he'd be dead."
Mr Tobeck's father, Paul Tobeck, said his son was still in hospital but had only minor injuries such as bruising.
"He's quite with it. He remembers hopping in the truck, putting the seatbelt on, going over the bridge and then nothing."
Paul Tobeck said he would support a bravery award for Liam and Angus.
"If it hadn't have been for the boys I could be organising a funeral," he said.
"It's not very often a couple of young kids [do something like this], most times people stand at the top of the bank and look. I hope these boys get the recognition they deserve."
Paul Tobeck said he and his son would buy the boys a $50 voucher from the local mall to say thank you.
Investigations into the cause of the crash are ongoing.