Hydro. The 1531 is only available with hydro.
I've been thinking about this all day. One thing I noticed, that I thought was odd. I was test driving it, actually the Cat version, but it's the same tractor, and I noticed that the slot for the lever was L shaped. Meaning it looked like it had a locking slot. I looked at the label and it indicated that up unlocked the diff and down locked it, which seems like what everything else does, so it made sense. It didn't make sense to me why the locking slot would secure the lever in the diff unlocked position and I double checked that label to make sure I was seeing it right, but then just wrote it off as "there must be a reason".
It occurs to me now that it's entirely possible that someone put the sticker on upside down on the tractor I was driving. That would mean that you would pull the lever up to lock the diff, which would be the reverse of every other tractor I've seen, but would make sense as you could then move the lever over into that locking slot and have the diff stay locked.
I'll certainly confirm this when I'm looking again, probably on Friday. Anyone have a manual handy to verify this?
Thanks,
Mike