About two days ago, my Amana alw480daw washing machine has started acting up during the spin cycle. The regular wash cycle goes just fine, but during the spin cycle, rather than actually spinning, the tub moves very little while the machine makes a very loud ratcheting sound. To figure out what was causing the noise, I removed the front panel and let the machine do its thing while I watched below. I quickly found out where exactly the noise was originating from, but I'm clueless as to how to proceed from here. I've attached a picture of the mechanism where all the noise is coming from. To my newbie eyes, it looks like it's doing what it's supposed to, but that can't possibly be right. During the wash cycle, the belt spins the shaft counterclockwise, and the top and bottom piece in the center of the photo grip each other, like it's obviously supposed to. During the spin cycle, the shaft is rotated the opposite direction, and the two pieces slip past each other, producing that loud sound.
Some extra info in case it helps:
-The interior has no obvious signs of rust or leakage
-The belt is breaking/shredding in a couple of spots. It still appears to be working as intended, but I plan on replacing it regardless of whether it's the cause of this particular problem or not.
-When I try to spin the tub by hand, it doesn't move freely. I have to grip it with both hands to get it moving in either direction. I don't recall whether it's supposed to or not, though, but I figured I should mention it here just in case.
I'm sure I would be able to replace any needed parts on my own as long as the procedure is not overly complicated, but other than replacing a broken drain hose, I don't have any experience repairing a washing machine. If anyone has a solution, please explain it with this in mind. Thanks.