the real tank has clutch and brake. but old tamiya ones only had clutch. that means, even one side is disengaged, but it is dragged along by the moving track because there is no brake. I tried brakes on disengaged side, it worked fine. tank will drive just like real tank.

your clutch gearbox has two motors too, you either can set it up with one big gear in the center or two smaller gear on each side. that way, you can use the old sherman gearbox to be controled by DMD unit. the only modification is to cut the chuncky clutch head, tricky there though.