Hi Bob,
Just wanted to make a couple of points about my first post on the thread...
</font><font color="blue" class="small">( 3RRL, many of your thoughts echo my own with one exception. If the toplink were level and the implement, in normal operation, encountered a major obstruction; the toplink would be in compression as the implement tried to pivot forward around the lower lift arm attach points. This would place a forward acting (pushing) force at the tractor attach point while the lower lift arm attach points would be subject to rearward acting (pulling) forces. The implement might not pivot away from the obstacle.)</font>
Yes I agree with that principle as I tried in my feeble explanation. /forums/images/graemlins/grin.gif
</font><font color="blue" class="small">( If the toplink were angled up toward the implement the implement could rotate around the top link attach point and tend to lift itself over the obstacle. In so doing the lower lift arms would raise freely to help with this.
If the toplink were angled down toward the implement, I think it would be much like the level toplink case except the implement would definitely not pivot. The hitch mechanism would bind because the lower arms would resist being pushed down.)</font>
Well, at this point I would say the top link is a rigid brace and regardless of it's angle, it would not allow the implement to pivot, as you mentioned about the tractor front raising up.
</font><font color="blue" class="small">( I can remember hooking a 2 bottom moldboard plow on a big tree root once and the only pivoting was when the front of the Ford 4000 pivoted skyward. Come to think of it, the toplink may have been angled down toward the plow on the Ford.)</font>
In my first response I wanted to point out that on a boxblade the force to the blade causes a rearward pulling of the implement thereby making it WANT to pivot around the lower link pins, not that it actually does. The only way to really make the implement pivot on the lower link pins is to have swivel brackets such as used on a brushhog to keep the implement wheel in contact with the ground. Without the swivel bracket the brushhog moves up in the air when the tractor front dips down into a ditch or something.
In fact, a rigid top link will keep it from pivoting around the lower link pins. The implement raises up when it hits an obstacle because the lower link arms raise up....that is if it skips over and does not "dig into" it. I was referring to the stress the casting/tractor sees, that is reduced because of the angle of the top link (vector force) instead of a direct force, with the top link dead square to the casting.
As you said, we're probably making more of this than necessary, but when you opened the thread it really got me thinking about the forces and such, not so much what the manual says to do. </font><font color="blue" class="small">( Pick a hole that works and go with it has its appeal. That's pretty much how its' done with Ag tractors.)</font>
That's pretty much how I feel about it too, although my manual also states to use the heavier ground engaging implements on the lower holes.
