The reason for the torque tube is that early manufacturers wanted the driving force to be transferred to the center of the vehicle. On open driveline models, the thrust to push the car/truck down the road is transmitted to the frame by the rear springs. With a TT, it goes to the back of the transmission housing and from there to the frame at the rear motor mount. Ford cars used torque tube drive from the Model T to 1948, and Chevy cars and trucks changed to open drivelines in the early 50's. American Motors (Rambler) used a torque tube until the mid-1960's. There are pros and cons to both systems, so "ya pays yer money and ya takes yer choice!"
