not sure I follow? If you have the outer half of the sprocket off, then brute force will get the inner half off the shaft.

If you have the sprocket off all ready, then there are 3 screws that hold each gearbox down - look for them between the gears. You also have to remove the outer covers from the hull to be able to withdraw the gearboxes - look for a small Philips screw above the output shaft on the outer hull - this will allow you to remove the cover and wiggle the gears out of there.

HTH,
Mart