Speedo calibration and/or axle ratio change

[Colin Cheesman]

Both the three speed gear and four speed are the same dimension internally, my solution is to machine a three speed gear to same width as the four speed, the only other modification is to machine the nipple off the bottom of the drive pinion from the three speed gearbox. Both gear and pinion drive will fit the four speed gearbox with three speed ratios.
Hope this makes sense.