Mido Macia was killed in 2013 when officers tied him to the back of a police van by his arms before driving off.
He was found in a pool of blood in police custody.
Judge Bert Bam called the killing "barbaric" but acknowledged that it was not premeditated.
Sentencing the men, aged between 25 and 56, Mr Bam said: "The continuous conduct of the accused concerning the injuries on the deceased was barbaric and totally inexplicable.
"What made their conduct more reprehensible was their cowardly attack in the cell on a defenceless and already seriously injured man."
A lawyer for the former officers said they would appeal against the murder conviction.
The sentencing of these officers sends a message that police brutality will not be tolerated by the judiciary, following several recent cases.
Judge Bert Bam sent a clear and unambiguous message that while the police are facing an onslaught from ruthless criminals - more than 60 police officers have been killed on duty this year alone - they cannot take the law into their own hands.
Another important factor here was the power of video material which is increasingly used as evidence in court.
No-one knows what would have happened if a bystander had not filmed Mido Macia being dragged behind a police vehicle with both his hands tied up. He was later found in a pool of blood in a holding cell.
There is huge public opinion support for the police as they try hard to keep communities safe against gun-toting thugs. However the people of Daveyton and indeed all South Africans will now be reassured that the rule of law prevails, even against the police.
Police pulled over 27-year-old Mr Macia in February 2013 after he allegedly parked a vehicle illegally in Daveyton, east of Johannesburg.
Following a struggle, they overpowered the driver before handcuffing him to the back of a vehicle.
He was later assaulted in his cell and died from head injuries and internal bleeding.
The incident was filmed by a bystander and caused outrage among rights groups.
A judge has sentenced eight former South African policemen to 15 years in prison for the murder of a Mozambican taxi driver.