Long ago, Mainspring was a component of Nexus Prime, the first combiner. To protect the shattered Star Saber from the Fallen, he split himself into five robots, each carrying fragments of Nexus' many artifacts: the Blades of Time, the Cyber Caliber, and the star Saber itself. The robot who would become Mainspring landed on Velocitron, and his landing site was thought to be haunted.
Over the millennia, Mainspring forgot all memories of his past life as he ascended to become the chief of Blurr's pit crew in the city of Delta. An inkling of his ultimate destiny evidently lingered in his mind; due to his habit of measuring time and tinkering with machines, he felt that he never truly fit in on Velocitron, bored by the constant racing.
When the Autobots arrived on Velocitron, Mainspring was part of a crowd of Velocitronians who admired Silverbolt's speed and airborne alternate mode, flying Transformers having been extinct on Velocitron for centuries. Soon after Jazz completed repairs on the Space Bridge that would take the Ark on the next leg of their journey, Mainspring approached Optimus Prime and asked if he could come with the Autobots.
By the time that Prime returned from a Matrix-induced vision, Mainspring was one of the bots who helped to repair the Ark after a saboteur planed a bomb near the starship's fuel supply. Mainspring and Clocker — another fragment of Nexus Prime — joined the Autobots as they made preparations to depart, but were attacked by Decepticon sympathizer Ransack and his followers, intent on claiming Velocitron for their own in advance of Megatron's arrival. Mainspring and the other Autobots struck the first few blows, then escaped in the midst of battle.
When the Autobots reached their next stop, Junkion, the Ark was damaged by another explosion. Mainspring was the one overseeing the diagnostic subroutine on board the ship, which would've let him know if the explosion had been an accident. Prime assigned Mainspring to assess the damage again, along with Clocker, Jazz, and Ratchet. After the Decepticons arrived aboard the Nemesis, Mainspring took part in the battle and used his dual energy cannons to damage Starscream. As the Decepticons used their warship to pry the Requiem Blaster out from the center of Junkion, he escaped with the rest of the Autobots as the artificial planet began to crumble.
Joined by the Cybertronian refugee Chaindrive and the Junkion scavenger Pinion, the presence of the four unique Transformers inadvertently awakened the fifth and final member of Nexus Prime: Cannonspring, who had slumbered beneath the surface of Junkion since ancient times. As the Autobots regrouped, the five Transformers briefly combined into Nexus Prime once more to hold off Megatron and Thundertron's Star Seekers, using his arsenal of ancient weaponry to great effect. After briefly providing some words of encouragement to Optimus Prime, Nexus split himself once more, and the five new Transformers flew off into deep space.