2009 Ltx1045 deck belt
 

I have a 2009 cub cadet ltx 1045 with a 46 deck
The mowing deck belt is loose, to the point you could almost take it off the crank pulley by hand.
So i purchased a new belt, now it can be taken off by hand.
Its the same belt number as the one i took off...measures 103 inches
When u activate the pto it does apply tension but not enough.

Any advice to why its so loose?

I have never seen one, let alone worked on one.
But the first thing I'd check is that the idler belt take up system is operating as it should,because that is what tensions the belt.
Those newer throw away lawn mowers tend to
not have greasable piviots,
and the few that do, folks either don't know about them or neglect maint.
Hope this helps.

Had the same thing happen on my 1045 a couple years ago. The bolt that holds the idler bracket had become loose and was causing slop in the in the idler.
Another thing check, make sure the springs are in good shape.
Check out the parts diagram here.

http://www.partstree.com/parts/cub-c...-deck-46-inch/