3-Point Hitch Top Link Bracket Positioning

[Jack3489]

Background: My tractors have three position top link brackets which allow the top link angle (between the tractor and the implement) to be changed depending upon which position is selected. These brackets have three different positions which are 1 and 1/2 inches between pins. I've read several tractor operational manuals and while they give general guidelines on different positions there is no definitive information regarding the theory behind the different adjustments or specific operational guidance.


My Observations: First, it is very evident that changing positions top to bottom will effect the rear lifting height of the implement when the 3 point hitch is raised. Selecting the bottom position (assuming the top link's overall length is not changed) will raise the implement's rear height to the maximum level. However, the real issue I'm researching is what effect the different positions have when the various implements (plows, box blades, mowers, rakes, etc.) are in their working position? It appears to me that the implements work better when the top link is almost parallel to the ground.


My Questions: First, does anyone have a link to a detailed discussion of the theory and effect different top link bracket positions have on implement operations? Secondly, I would appreciate your operational experiences regarding this issue. What works best for you when using a specific implement?

Thanks,
Jack

 

[murphy1244]

the top hole is for implements that are not ground engaging the center hole is for light ground work and the bottom for heavy ground work.

 

[whistlepig]

In my experience the different positions on the top link bracket are just and additional way to make adjustments to the top link if needed. The lower arms control the working height of the implement and the top link is there for raising the implement. Having the top link parallel to ground doesn't work for most of the implements that I use.

 

[Treesanddust]

If your tractor's three point hitch has Draft ability, the hole options will usually affect the draft operation.
Your tractor's manual should tell you which hole to use for each type of work you're doing.

 

[/pine]

What Murph said sounds good to me...FWIW my k ubota manual says: "the top hole is "standard" and use the bottom hole when there is "some object" that prevents using the standard"

I moved my top link to the lower holes when I added a hydraulic top link for more clearance when the 3ph was all the way up...

 

[Guesseral]

If your tractor's three point hitch has Draft ability, the hole options will usually affect the draft operation.
Your tractor's manual should tell you which hole to use for each type of work you're doing.

The three different holes are definitely an adjustment for the draft control, I can't tell you all of the particulars but I can give you a better idea. The draft control is basically an automatic adjustment of you hydraulic system depending on the amount of force placed upon it by the implement being used and the type of ground in which it is being used in. The top link bracket is like a lever the bottom is the pivot point and depending on which hole you place the top link will determine the amount force placed upon the plunger in the draft control. For example the bottom hole would place less force on the plunger than the top hole because the top hole (because of the lever action) would offer less resistance. The more force placed on the plunger the greater the action taken by the hydraulic system to reduce the resistance on the tractor itself. The draft control operates to reduce drag on the tractor as ground engagement equipment drags in the soil so the tractor RPM and speed isn't changed during a chore (plowing is most common) because as the plunger is pressed in but the force created by the drag created by the ground the hydraulic system will automatically raise and lower to keep a constant RMP and or speed. That is a very basic sequence of operation, but for most of us with newer tractors the different positions really only help as top link adjustment because the draft control function is defeated by a stopper placed between the top link bracket and the hydraulic cover so the draft control does not function unless the stopper is removed. I assume the manufactures installed this stopper because all 3pth hitch functions do not require draft control and by defeating the function there isn't any ware and tear on the draft control linkage inside of the top hydraulic manifold.
Well that's my take on the subject, lets see just how many different readers tear it up!:confused3:

 

[RoyJackson]

the top hole is for implements that are not ground engaging the center hole is for light ground work and the bottom for heavy ground work.

This comment follows what the Deere manuals (for compact tractors) describe.

 

[Jack3489]

Thanks for detailing your practical experience. I still find the various tractor operator manuals short on explaining the "why" regarding positioning selection. Most just give general suggestions at best.

I wish someone could provide a link that explains the theory of the design?

Maybe the folks who supply aftermarket top & tilt replacement parts know?

Jack

 

[Baby Grand]

The kinematics of the 3PH are affected by changing which hole the top link is pinned to.
The 3PH behaves as a 4 bar linkage, and changing which hole the top link is pinned to changes the ground bar length (the distance between pivot points on your transmission/frame).
This affects not only lift height, but also affects the shape of the curve that the implement follows through its range of motion as well as the lift capacity.
If you take 4 drinking straws and pin them together you can quickly get a feel for how changing this geometry affects how your implement behaves, especially if you scale the distances between the pins to measurements taken directly from your tractor.

Four-bar linkage - Wikipedia, the free encyclopedia

By changing which hole the top link is pinned to, top link length and the length of the lift arms and drag link length (some tractors have different pin positions for these, too), you can get a large variety of different motions.

 

[Kioti Tom]

The use of the different toplink holes started with the Ford 9N. They had the draft control
system which uses the toplink to provide sensing for the automatic movement of the hydraulics
to compensate for ground hardness for instance like when plowing. When harder ground
is encountered, that will cause the toplink to push on the toplink fitting and the hydraulics
will lift the plow slightly to clear the area and then return when softer ground is entered.
The 3 hole fitting did not come about on the Fords until the later 8N's and later. The fittings
were cast so the piston attached by the lower attach point and then the 2 other holes were
higher. Using plow for example, attached to the top hole many times broke the link
bracket. So something like the weeder, or some light equipment would be used there.
medium duty equip. used on the center hole and heavy ground engaging equipment
the bottom hole as that was the strongest point and direct sensing at that point.

Clear a glass., I know. Google the Ford 3 pt explaination for more added info.
I just gave the basics..Not an expert in any case

Tom