I've posted a video on how to solve the Gear Shift here - http://www.youtube.com/watch?v=-zjGKPxbFLs

The mathematical explanation of this solution is that when you rotate the top, then re-solve six gears, the number of turns which both the top front left and bottom front left go is double the amount of the first rotation you did. Hence you rotate half the first time to solve the top front left, then you do complete rotations of the top front left for each unit of the bottom front left, because each complete rotation is eight units, which translates to 16 units once everything is fixed, and 16 mod 5 is one.