Roofus

I have looked at the parts manual. Unless I'm missing something (I hope I am, and someone points the part out that is right infront of my face). I just need the aluminum part that appears to house the axle/brake for the rear end. The chain doesn't keep enough tension the way it is right now. I found this quad at the dump and got it running, just need to replace whats broken in the picture.

I cant seem to find what this part is called. Can anyone point me in the right direction? I must be misinterpereting the parts catalog or something? I dont see it in the rear axle section. I think it may be in the rear brake assembly section? click link to view picture.
 

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