As with your tractor, my loader can raise the front of the tractor off the ground, even with nothing on the 3PH. But, it doesn't do it all the time.
Something I've noticed:
With the loader bucket firmly on the ground, and applying down pressure, the rear wheels will roll forward slightly as the front wheels come off the ground. With the hydro trannie in neutral, the front wheels raise easily. With the parking brake set, no way...the front wheels won't even begin to rise. With parking brake off and hydro trannie engaged...maybe yes, maybe no. With the tractor sitting still and trannie engaged, there is some degree of braking automatically applied as part of the hydrostatic circuitry. I believe when the tractor is sitting still, the amount of braking power varies a bit for no clear reason. When there's less braking, the wheels rise; when there's more braking, they won't.
Here's the TEST:
On a level surface, put the transmission in neutral and try to raise the front wheels. They probably will go up easily.
Next, try the same thing with the parking brake set. Probably won't go up at all.
Next, release the brake, put the hydrostat in Hi range and try again. Maybe yes...maybe no?? If yes, then go to the final step.
Finally, put the hydrostat in Lo range and try one more time. Is it different than in Hi range??
As mentioned in a previous post, I have noticed less power in hot weather (hot hyd. fluid), but I also think transmission braking has something to do with being able to raise front wheels on hydrostat tractors. If you try the test, let us know.
OkieG