Why is this such a issue with the Kubota, the lighter JD 790 didn't ever lift the rear. Would the smaller turf tires be the difference?
Every single tractor has a weak point.
Loader frame
Hydraulics
Front axle
Tractor frame
Tires
Proper rear ballast
Probably more I can't think of
Of all of those, hydraulics, specifically the hydraulic relief valve is the best one to run into.
On my Grand L it's either the hydraulics or front axle bearings. With loaded rears & no 3pt ballast I can't lift the rear. I did that once gently without moving to test. Probably didn't help the the wheel bearings that got replaced shortly before warranty was up.
On the economy Ls, specifically my
L3200 I could lift the rears with heavy rear ballast. It would lift "1,200lbs" hay bales (pluss a few hundred lbs for the pallet forks), although it felt sketchy doing it. My new
L4060 tops out at a 1,700lbs lift or so but weighs something like 1,500lbs more without loaded tires (which are way bigger & heavier) or ballast. So bang for your buck the
L3200 had way more lift. But it had more lift than it probably should have. The actual rating for the loader on the
L3200 was way less than what I lifted with it. The LA805 on my
L4060 is rated for 1,700lbs or so, which I can only barely exceed when you add in pallet forks & the leverage of junk hanging a ways forward of the forks.
I'm guessing your 790 just had less lift to tractor weight than the economy Ls. Less useful, but safer.