I've been wondering what is the advantage in the single or unitized hydro pump JD uses on their ZTR. I'm not sure if all of the JD ZTR are built this way but I do know the 737 & 757 are like that. I was told by a JD salesman that it provided a more even tracking over the two pump system...?? Just wondering what any of you may know about their reason for this. A freind of mine has a very old Great Dane 61" 25HP ZTR that has one pump...could this be the same thing JD is doing now? Thanks for any responce on this subject.