We put about 80 miles on, when I started to hear the chain slapping around. So I got off and noticed the chain was super loose. So I had to drive about 8 miles back to the truck and just as i got to the truck the chain snapped off. Upon looking at when, after I pushed it on the trailer that the seal on the right side was out and what looked like the cage for the bearings was hanging out.

So I know what I have to do, but was wondering and looking for insight on why it happened.

 

Unless the two 5/8" bolts and nuts that tighten the rear bearing carrier loosened up allowing the chain to have slack or the chain was loose to begin with. Plus the most of the ones I had with bearing problems weren't kept greased enough and bearing wear could be the main problem especially since the seal was out along with the bearing. The two axle nuts could have been loose,but that's the purpose of the second nut to keep the first nut from getting loose. The older models were bad on this and I replaced many bearings and races and seals on the straight axle models. You could jack the rear end up and feel the bearing play. OPT