Abstract: A power transmission assembly for an agricultural machine includes a gearbox having an input shaft, and a torque sensing assembly having an axially fixed sheave, an axially movable sheave, a cam assembly interposed between the axially fixed sheave and the axially movable sheave, and a spring assembly coupling the axially movable sheave to the axially fixed sheave. The axially fixed sheave includes a hub portion having a tapered face extending increasingly outward from an inside diameter to engage a beveled shoulder of the input shaft. A nut is engaged with a threaded end of the input shaft, such that when tightened the nut forces the tapered face of the axially fixed sheave into engagement with the beveled shoulder of the input shaft.