The gear that is engaged to the transmission is running constant and the second gear shifts onto it when the PTO is placed in operation. This allows for different ratios and power than can be had by that available directly from the drive gear of the dransmission. It also allows the distance or c/l of the pto shaft to be further from the transmission and makes for a lot more application variations such as direct drive pumps, air or electric shift, etc. Yes, I realize that there are 6 bolt units like you have and I said most or generally they are 8 bolt and that is true.
