The ATS Billet input shaft is the back bone of your Ford Powerstrokes transmission. It is the first hard part to bring power into the transmission and transmit that power to the wheels. With no dampening or power loss other than the torque converter, the input shaft has a lot to handle. Now add power, weight from a trailer, bigger tires (and is some cases all these things together) and you will be well beyond what that factory shaft was designed for. The theory behind billet shafts is not quite what you may have in mind. The key to success is not to make the shaft stronger necessarily, but give it the ability to absorb more torsional load. The way we do this, is by using billet shafts, they have the ability to rotate further with out breaking. This is going to give the transmission more give and allow it to transmit more torque and more load with out breaking. Along those lines, breaking an input shaft can be catastrophic to your transmission. Sometime when the shaft breaks, your truck will simply stop moving and it needs a new input shaft. Other times, when that shaft breaks, it can take out your torque converter, front pump, and front seal as well. Obviously this is going to be a very costly repair. Then add on top of that labor time, fluids, new gaskets and seals, and you can quickly see how this can add to the cost fairly quickly. It is simply good insurance to hold reliable power in your transmission, to add at minimum a billet input shaft.