Paul,
Quite a lot, as it turns out, and I have pushed mine to the literal breaking point.
Two years ago I built a hydraulic front-end loader for my E20, and when I added the measured weights of each component of the loader, it adds no less than 500lbs to the stock weight of the tractor. That brings it to 1,400 pounds, and then I built
a weight box which mounts in the rear frame stabs and adds *another* 500lbs counterweight when fully loaded with containers of lead tire weights. That's a total of 1,900 pounds with not an ounce in the bucket. I once have put just shy of 500 (or was it 600?)
lbs of bricks in the bucket (bricks, so I could "measure" the weight by counting the bricks - hard to figure out how much a load of gravel or dirt weighs) bringing the total to 2,400lbs. And so far, that was fine, though of course I drove around very gingerly.
I also added 24" ag lug tires filled with 65lbs of RV antifreeze. While this load is not on the axles, it makes the tractor weigh even more and provides more traction. I have a lot of grip in the dirt...
Earlier this Spring I was digging in hard clay dirt with the bucket, trying to take a pretty good swipe out of a rise in my property to level it out. I did so with the full 500lbs counterweight and I foolishly chose "LL" or first gear, which
I now know has the astounding gear ratio of 174:1, in addition to which the drive motor and transmission driven pulleys add another gear reduction. All this was too much for one of the axles, and it sheared at the outer end where the woodruff key drives the
hub. I was lucky - on a stock tractor the wheel would have simply fallen off, and the tractor may have flipped. But I had just added auto drum brakes to the rear wheels (in order to actually stop the 2,400lb beast), and the drum simply rested on the brake
shoes and didn't go anywhere. I purchased an axle and other spare parts from Harold and with those, it was back on four wheels pretty quickly. Note this incident was due to excessive torque, not excessive loading, but I think I'm also probably near the ragged
edge for loading as well.
I learned my lesson and now I dig, or drive into a pile of material (dirt/gravel) in D (3rd gear) if I can, or I use L (2nd gear) sparingly. I pretend LL doesn't exist. I also run with only about 300lbs counterweight unless I need more for safety.
I prefer to hear my drive belts slipping than to break the transmission again. I have moved more than 40 tons of dirt and gravel with the tractor and, aside from my foolish digging mistake, it seems no worse for the wear. I have been meaning to weld in braces
for the front axles similar to the "heavy duty" version GE offered, because the front axle takes a large majority of the weight when the tractor has a full load in the bucket (imagine the load and the tractor/counterbalance perfectly matched - the tractor
would balance on the front axle).
Good luck, it's a heavy duty tractor and it will serve you well.
Ben