Interposing the idler gear in between the countershaft reverse gear and the leading shaft even bigger gear, the main shaft turns inside the direction opposite to that on the clutch shaft. This improvements the rotation in the wheels from ahead to backward so that the car or truck backs. https://gearbox52074.blogpayz.com/33870222/how-much-you-need-to-expect-you-ll-pay-for-a-good-gearbox