[old Chevy guy]

You don't have to pull the output shaft. If it's a two wheel drive you should be able to pull off the Tail housing ithe gear slides on the shaft. I forget exactly but there may be a clip or something. That gear Is nylon. I'm assuming that's what your after,there's two gears one on the shaft and one on the end of the speedometer drive. The drive one you can get to by just pulling the drive out. One bolt and a small metal braket hold it in. The gears are color coded to determine gearing to match the speed depending on rear axle ratio. Why do you want to change it? To get the one on the shaft you will have to jack up the unit remove the mount and driveshaft then 4 bolts on the tail housing and I'm not sure but I think you have to pull out the speedometer drive. You may want to pull the crossmember to make it more accessible. Have a drain pan read as you will lose lome ATF when you pull the shaft and more when you pull the tail. You can't remove the output shaft without dismantling the unit,but if it's just the gear you don't have to. Post more info on what your end goal is here so we can answer better.