The sparrow has to be rare (blue background) in order to use the drive. Once a sparrow has been upgraded to legendary, it is no longer eligible for the upgrade.
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Yea its already upgraded. But thanks for answering the question so I down waste my coins on another one.
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No problem. I wasted my own coins trying to figure it out. I wanted to change the trail color on the timebreaker but since that's already legendary, it's ineligible. I have no idea why they would put purple trails on a red and tan speeder.