We have two 8040 Knight slinger spreaders.  These spreaders had seen their better days when we purchased them a few years ago.  We fixed them up, painted them, etc.  Recently, we have had some trouble with the augers moving fore and aft.  At this point we aren't completely sure if the auger that is moving is the upper one or lower one, but the two sprockets at the back of the spreaders are not lined up causing the 120 chain to ride off the sprockets.  So, here is my question(s).

What specifically, keeps the augers from moving fore and aft?

When they do start to move, what needs to be replaced? 

This is also posted in Machinery Talk.....