It's a weird setup, it is an enclosed housing with a splined section for the drive sprocket, a splined section for the brake, and splines for the wheels. The sprocket and brake are thicker than the wheel splines, meaning that it tapers slightly from the sprocket and brake to the drive wheels. The only solution I see is an off the shelf axle, pillow block bearings, and welding on a hub for the drive sprocket and brake. I am kind of at a loss, I spent a bunch of brain power on the jackshaft, and the wife will whip my hind end if I lose sleep over this little problem.
Help with a design?