When she tried to escape into the back seat, Zabell continued to throw punches, some hitting the young boy.
Zabell had refused to stop driving and had threatened to kill the woman and boy, saying he would not stop hitting the woman until she was dead.
Arriving in Masterton, he had dragged the woman from the car by her hair and had ordered both his partner and the boy to undress because there was blood on their clothing.
Soon after, when his mother tried to intervene, he "back-handed" his mother, hitting her on the jaw.
Zabell also snapped his partner's cellphone in half.
When police later searched Zabell's car they found a baseball bat inside.
Zabell had claimed his partner had endangered their lives by pulling the handbrake on while he was driving and by throwing a towel over his face.
Judge Walsh said Zabell had 29 previous convictions, seven for violent offences.
He said a pre-sentence report indicated Zabell was a risk to others because of his propensity to violence.
"What you did was completely unacceptable and you are fortunate your partner and her son did not suffer more serious injury."
Judge Walsh said photographs taken after the incident and produced in court showed Zabell's partner had suffered a black eye, facial injuries and a bloody nose. She had spent a night at Wairarapa Hospital and suffered head pains for days afterwards.
The aftermath of all that was the woman was trying to cope with anxiety and depression, said Judge Walsh.
He said Zabell could well have crashed the car, killing all inside or others the car hit.
"In mitigation, I take into account you pleaded guilty and have written a letter expressing remorse.
"A lot of people are remorseful after violent incidents but remorse can come too late for victims," Judge Walsh said.
He said the court had to impose a sentence to deter people from committing the type of violence Zabell had displayed and that meant imprisonment.
The judge issued a protection order in favour of Zabell's former partner and imposed two special conditions to remain in effect for six months after Zabell's release from prison. These were that he was to undergo a family violence programme and attend any other counselling as directed.