The holes all depend on if you have draft control.
If you dont have draft control, they are simply there just to give you greater flexibility on how you want the implement to raise. The lower hole will give less lift force but raise the tail of the implement higher. The upper hole will give more power but less height.
If it is draft control....what soundguy said:thumbsup:
Out of my own curiosity I decided to continue on researching further, I have concluded this in general:
Standard 3 point hitch top (center) link position on any tractor with factory provided adjustment holes:
1 - Universally affects with varying degree the lift height of the rear of the attached implement. The lower the hole the higher the lift of the rear of the attachment with the opposite effect moving the top link upward. (with or without draft sensing on the top link as this a result of the standard 3pt defined geometry)
2 - Tractors without draft sensing refer to bullet 1.
3 - Tractors with lower link draft sensing no effect as draft control works independently with the effect of bullet 1 withstanding, however lift capacity could be impacted.
4 - For tractors with top (center) link draft sensing see bullet 1 in addition, the position of the link as related to the behavior of draft control and weight of the equipment is specific to the manufacture/model of tractor as some use the upper hole for heavy implements and some the lower as you must check with the manufacturer. This is due to the activation point of the reactive draft control factory pre-determined activation settings.
Many people generalize that top hole for light draft and the bottom for heavy but you should be very careful with that statement as I found reading the patent issued to one of Deere & Co top link draft sensing implementation, you see that their design used the top for the higher load. I do not have a list of tractors that this particular design is used on however it appear that it is the 1970s era 1040 maybe. Some of you JD Gurus can help me here and it still may be in use on JD top link draft sensing tractors today see -
My JD 3320 manual says the following:
For light and medium draft loads: Install center link in BOTTOM hole of mounting bracket. Example of light and medium draft load implements would include a landscape rake.
For medium and heavy draft loads: Install center link in MIDDLE hole of mounting bracket. Example of medium and heavy draft load implements would include a tiller or box blade.
For very heavy draft loads: Install center link in TOP hole of mounting bracket. Example of very heavy draft load implements would include a plow or ripper.
Mine came with the link in the middle hole so I just left it there for my uses.
Ref: Deere & Company Three-point hitch draft control US 4304303 A states:
"First linking member 45 has three holes 69, 71 and 73 to accommodate the attachment of upper hitch arm 43 to linking member 45. The magnitude of excess load necessary to cause raising of the implement 15 is determined by which hole 69, 71, or 73 used to accommodate the attachment of link 43. The greatest load is required by using hole 73 and the least load is required by using hole 69. The normal draft load is determined by the initial positioning of lift arms 29.
h) draft load sensing means for receiving draft loads from said upper hitch arm and mechanically translating said draft load to an angular displacement of said first shaft when said draft load exceeds a predetermined amount."
It is important to note, the upper hole indicated as 73 on the drawing is for the higher draft load referenced in the drawing in John Deere's patent so I would be hesitant to declare the lower hole is always the placement for heavy draft and may be tractor model/make specific.
It is also important to note that in the reference patent, the devices has a fixed draft specified by the statements regarding load exceeding fixed �redetermined amount affected by the placement of the top link, where as some tractors have adjustable sensitivities (mechanical or electrical) as opposed to this system suggesting that draft can be controlled elsewhere with a fixed position of the top link.
An example of this alternative is the use the lower arms for draft sensing which leaves the argument that the placement of top link usage in those scenarios has everything to do with angular position of the attachment and less effects on draft control if nothing at all.
Along those line, there is no reference to top link position in the draft control section and the top link instructions only refer to the height of the rear of the implement in this example of the JD 5075M operators manual and it is important to note that the lift capacity is reduced using the lower holes on this machine and this machine has lower link draft sensing:
Position Center Link
LV14570-UN-04AUG11
Bracket Inverted
A - Upper Hole
B - Middle Hole
C - Lower Hole
D - Lowest Hole (with center link bracket inverted)
The center link attaching bracket has holes which allow four different positions for attaching the center link.
NOTE: Center link attaching bracket can be mounted to provide hole position (D).
If the following conditions occur, move center link to indicated holes to correct.
Condition Use Holes
Rear of implement rises too much when lifted. 1 A or B
Rear of implement drags the ground. B or C
NOTE: Implements with Category I mast height 457 mm (18 in.) will normally use attaching holes (C and D) and implement with Category II mast height 483 mm (19 in.) will use holes (A and B).
1 The implement weight which can be lifted is reduced slightly with center link attachment in lower holes. JZ81662,0000443-19-20111011
Copyright ｩ 2013 Deere & Company.
All Rights Reserved.
In summary, I must apologize to you sherpa (OP) for offering an answer for what the two positions are for on the top link of your specific tractor without knowing the specifics of the tractor you referenced as I don't have a freaking clue.
Cheers
