Only the detonator on the 132 lb beer keg exploded in a hijacked Renault Laguna car at the entrance to Victoria Square shopping centre car park on Sunday, November 24.
The driver of the car was forced at gunpoint to take the bomb from the Ardoyne area to the shopping centre in Victoria Street.
The device partially exploded as Army technical officers were about to examine the beer keg.
The two men, aged 44 and 45, who were arrested on Wednesday, have now been released unconditionally.
Police inquiries into the attack are continuing.