Rear axle issues

Hi All, been a while since I’ve been on. Been busy. I’ve been doing a bunch of work to my new toy and now I have an issue I can’t figure out. I have a 97 300 fourtrax 4×4. I just put new back brakes on and now I seem to have no power to my rear end. I can’t even climb the smallest of hills. All kinds of power to the front. I tried backing the brakes off all the way. I can push the machine freely with no binding. But when I apply any kind of power there is nothing to the back. Pulled the side cover off and the shaft is spinning. And when I’m applying power it almost sounds like it isn’t engaging in gear. Not a grind but not a click. Somewhere in between the two noises. I’m looking in my service manual but havnt had any luck figuring out what has happened or what I did.

Any help or suggestions would be greatly appreciated

Thanks