It's tricky, but I would remove the assembly in two parts. First remove the planetary carrier but be carefull not to loose any disks and plates. I have put a piece of tin underneath the assembly during removal. That way when something falls out I don't have to fish it out of the bottom of the housing.  Then remove the hi low clutch housing using extensions. Tape the allen wrench socket to the extensions and tape the extensions together so you don't loose them. Be carefull with the bolts. They are easy to loose.
You will need to make a tool to compress the spring washers so you can remove the snap ring to take apart the piston.  My best guess is you have a broken packing around the piston or the disks are worn to the point they are slipping. Take a look at the groves of the disk hub. Make sure the disks slide easily. Any edges and the disks may jam and possibly break. Check them on the inside and outside. It all has to move smoothly or you will have trouble. I fought this for many years on our 8630. After getting into the hi low for 5 or 6 times, we finally decided to get the update kit with the helical gears. That solved it. I think you already have this in your 8650.

When you put the plantary carrier back intot he tractor, take a piece of wire and  strap the disks and plates so they don't fall off. It's easy to remove once it's installed.


Oh, there are a couple of vent hoses on the bearing quill ( lid ) which would be easier to remove before turning the tractor.  And if you haven't done so yet, pressure wash the hinge area before you get started or you will come out a grease monkey for sure.

Also, mark the universal joints before you remove the shaft, so that you put it back together the same way it came out. Try not to take off the caps if at all possible.

Good luck

I have the manuals for a 8630 and 8640 which should be very similar to a 8650. I can scan and send them to you if you like.