If the shear pin breaks and the operator does not stop the machine, this is what happens. We see it quite often on our Walkers. Once the shear pin breaks, it allows the drive shaft to continue to spin on the input shaft but there is no direct connection since the roll pin is only there to hold the shaft in place. In addition, if not caught early enough, the input shaft on the center box will be worn as well requiring replacement. The input shaft on the center box is available as a service part and can be replaced easily.