Axle Nut Loose!!

Ok, my right rear axle nut keeps coming loose and makes my wheel and drum move all over the place. Last time I tightend it I torqued it down to 253ftlbs and used a new cotter pin. Now, I am replacing the transmission I decided to shake the wheel to see if it was staying tight. I shook it and it wobbles like crazy! What is goin on, and what do I need to do to fix this? Oh yea, I tightend it down about a week ago.

Might try getting a new drum, new, not used. They're less than $50, try shopping around, German ones are the best. Mine had that problem and turned out to be the splines were wearing away. I ignored it when I was young and not so bright, till the splines were gone and I was stranded.

Yep that was it. It left me stranded a couple of days ago, got it home and looked at the drum and there where absolutely no splines inside the drum but the axle is just fine. So I will be getting a couple of drums this weekend.