As you can see, the rock, which is visible in the foreground between
the impellar and shaft, caused the shaft to break.
 
 
 

This picture shows the blades of the impellar.  Notice the extensive damage.
The rock had apparently been in the pump for a while.  The rock did show
signs of having been broken by the blades of the impellar prior
to the breaking of the shaft.

Two weeks of chasing parts, and $1,500.00 later, Truck-2 is again operational.

WATCH OUT FOR THOSE ROCKS!!!