Ok, I'm showing here, my CAD view of the gearbox I have, and the photos of it split in half, (it's quite greasy). Keep in mind that the one I am using is actually for a go-cart and is approx. 6" square. However, I think it could be shrunk and used in a 1/5 no problem as it is a simple design. I will attempt to describe how it works if it isn't easy to understand.


When it is opened up, we see an input shaft driving a pinion gear. This pinion is in constant contact with 2 larger bevel gears, forcing them to spin in separate directions. These gears ride on a shaft, but are not attached to it. Between these bevel gears is what I will call a "locking mechanism". It's basically a bearing with steps on the side, that lock into the steps on the bevel gears. This locking bearing rides on the same shaft, and IS attached via a key slotted in the shaft, therefor always spinning as well. Depending on which bevel gear the locking bearing is locked to, determines the direction of the output shaft. The locking bearing is slid between the two gears by a pin that comes thru teh housing, and attaches to the mounting plate of the bearing. By sliding the pin in, you engage one gear, giving you forward, pulling it out half way gives you neutral, and all the way gives you reverse.


Haven't figured out a way to make this an inline case, but for my use 90 degrees is perfect. I plan to hook the output of the engine directly to the input shaft on the tranny, which will be placed below the engine, via a chain, and then one chain to the front, and another to the back. Option B. and the one I want, is basically the same idea, but turn the engine sideways, drop a chain to the now sideways tranny, and run shafts from both sides of the output to the shaft driven diffs, (if I can figure out how to make those).