David Miller

I have an RZ4621 that is having issues in not being able to go up hills.  I have replaced the drive belt, and purged the hydrostatic transmission.  My concern is the tension of the drive belt.  It appears to be "locked" in place, the only way I can increase or decrease the belt tension is via a hammer.  The repair videos show this as being able to be moved by hand, which is logical having the spring providing the necessary correct tension.  

How do I free up the tensioner so the spring provides the proper amount on tension to the drive belt?  I assume it has to do with loosening the nut shown on the attached photo, however do I loosen the upper or lower nut?  I tried both a bit to no avail, however I didn't want to lose any structural integrity, so I retightened them.

As an aside, when I increased the belt tension via hammer, I no longer experience the power loss on hills.

Thanks in advance,

Dave