93 F150 4 wheel drive question

I just bought this vehicle and don't know much about trucks. When I put it into 4 wheel drive, the drive shaft spins and I can see it spinning at the wheel. It makes a clunking noise. I have both wheels locked out at the hubs. It only seems to spin on one side. I am assuming something in the hub is broken. (the reason why I can diagnose this problem is that I am stuck in the snow and the rear tires are slipping)

Is this something relatively easy to replace? Is it a common part? I do all my own work so I'm used to fixing things.

Thanks

If its got lockout hubs, you can buy a new pair for less than $100. They are easy to change. If you have a stripped out hub, gonna cost a bit more. The reason only 1 axleshaft spins up front is that it is a open differential.