Either side of the steering clutch units , is the unit that forces the pressure on the drive clutches, and it also has a carbon footbrake band unit attached, this unit I call the Heli-hub unit as the sideways pressure is transmitted via a helical thread in a bronze hub. The turning motion of the Heli-hub is by way of 2 chains rapped around and connected to rods that run to the front of the driving controls . Adjustment pressure to the clutch plates is achieved by a bronze ring, that you rotate in and out, and then very important to re-lock the ring as it can undo itself when the Tank is in motion, and therefore you lose drive. Up front of the Tank in the driving controls are two special little over-centre devices that can increase pressure to the clutch disc's in an emergency , if you are losing drive ,so you do not have to get out of the Tank.
Cheers from the Tank Factory.