Deck height adjustment

Just took delivery of a new to me 2007, 720 w/54" deck. I was playing with the height adjustment knob to get to the setting that I used when I borrowed my neighbors mower. The knob is very hard to turn, I had the deck all the way in the up position. On my neighbors it turned with a lot less effort = 36 or 48" deck. Would the lighter deck make a difference in the amount of effort it takes to turn the knob, if not what should I be looking for or do to remedy this situation?

Thanks
Dan