They drive them "through". Front unit is driven off the rear shaft.
Could you hydraulic drive it..... I suppose you vould. But that would be expensive and unnecessary. If you're going to do that, just use a mounted hydrostatic pump on the engine, remove the hydro units off the rear ends, and mount piston motors. Then split drive them both.
I want to see someone build a gear drive articulated tractor. That would be impressive! I've seen one, but it had two gear shift levers. Not impressed.
