shimming guide...

Shimming your gearbox is one of the most important things you can do when working on your aeg gearbox. Proper shimming allows for easy movement of the gears while at the same time reducing the amount of bounce that your gears experience. CAUTION: Overshimming your gearbox will cause excessive friction and drag on your motor and battery. Undershimming your gears can cause a bouncing action in the engagement of your gears causing extensive wear on your gears and bushings.
REMINDER: This is only a starting point for the proper shimming of your gearbox. Each gear may require more or less shimming. If excessive shimming is need you may have a deformed gearbox shell.