Mr. Ignorant here....
I'm pretty sure both (IH) tractors we have here (444, 1066) have draft control. Never have need to use them since tractors are essentially large lawn mowers.
So for those not well versed with what is exactly happening if the draft control "gets in the way"....
What is exactly happening?
I THINK I understand that the draft control LIFTS the 3-point so if you are plowing and the plow starts to dive deeper into the ground, the draft control lifts it back up to keep that from happening.
Presuming that to be reasonable and accurate, the 3-point only moves so far. What's happening to make this a dangerous situation?
(side note, tractors like I said are lawn mowers, my backhoe is hard mounted so I don't have this concern/exposure so am trying to learn)
You have the understanding of how it works basically correct. The automatic draft control responds to top link compression by lifting the 3pt arms when the load on the implement is increased.
That increased load happens when a plow either goes deeper or hits a rock or root - all of those cause the top link to be put into compression.
At the tractor, the top link connection which seems so rigid is actually a very heavily built pivoting spring mount that triggers the auto draft control when the pivoting mount moves a fraction of an inch. It takes tons of compression to trigger the automatic draft control, but when it does, the reaction to raise the 3pt arms takes place in an instant. Usually raising the arms an inch or two will allow the implement to rise enough to clear the obstruction. As soon as the plow clears the obstruction it returns to the previous depth and all is well.
But with a backhoe pushing down to lift the tractor - as long as there is downforce on the bucket the compression on the top link can't go away, and the arms will continue to raise until they are all the way up. Crushing anything in the way against the back of the tractor. The lift arms go up in a series of violent jerks as the auto draft control works at max pressure in conjunjction with the 3pt relief valve. Everything bounces, shakes, and pops as the arms raise and crush the intervening parts. The draft control lift system cycles so fast it sounds like a a machine gun. This all happens so suddenly and is so violent that it is hard to keep your wits working.
As the lift arms raise under unusual pressure they may only move an inch at a time but they do so several times a second. That's necessary when plowing of course - which is the purpose of the auto draft control in the first place. And it is why the lifting force is to unusually high and the motion so abrupt.
When a 3pt backhoe is fitted between the lift arms and top link it is compressed right along with everything else in the way as the arms lift. It's not uncommon to break the top link mount and bending the top link as well as squashing everything in between arms and top link.
Safety strut systems are one answer, and are simply beefed up extra struts that are stout enough to keep the lift arms from raising. That requires some serious steel. The problem there is that the forces are so extreme that if the strut holds, something else breaks.
Hope the explanation helps. It isn't a problem if you just remember to turn auto draft control off.
If you do a lot of backhoe and little plowing it would make sense to disable the auto draft control completely. Draft contro is a feature big Ag uses, but most of us do not.
rScotty
