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

 

[Jack3489]

Tom, I've read the history of 3 point development in England and that the original concept used draft control to lessen the impacts of plowing on the tractor. However, many "modern" tractors (like my two) have a fixed 3 position top bracket with float implement positioning control (thus no interactive draft control). Guess I'm still puzzled regarding the theory behind which position to use on these modern fixed brackets.

I certainly understand that the top link is typically in a compression mode when using heavier ground turning implements and that this compression assists with traction by putting pressure on both the rear and front wheels. I assume the angle between the top link and the implement determines how much force is produced.

I'm still surprised that we (as a collective group of experts) have not been able to find any definitive link that details the concept / theory. I keep looking!

Thanks again for everyone's input.

Jack

 

[Dan Hunter]

From my jd 3720 manual:

• For light and medium draft loads: Install center link (A) in bottom hole (B) 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 (C) 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 (D) of mounting bracket. Example of very heavy draft load implements would include a plow or ripper.

 

[bandaidmd]

Interesting discussion but no real answer yet. To muddie up the replys why do tractors that dont have draft control still have 3 holes and Dans manual has it completely backwards from the other posters manuals.

 

[RoyJackson]

Interesting discussion but no real answer yet. To muddie up the replys why do tractors that dont have draft control still have 3 holes and Dans manual has it completely backwards from the other posters manuals.

It's a matter of stress loads on the tractor...

 

[RoyJackson]

Interesting discussion but no real answer yet. To muddie up the replys why do tractors that dont have draft control still have 3 holes and Dans manual has it completely backwards from the other posters manuals.

It's a matter of geometry and stress loads on the tractor. Different tractors have different upper link bracket locations.

 

[Jack3489]

I agree this is a great discussion.

During my research I've also noticed that John Deere and Kubota manuals are diametrically opposed to each other in their recommendations! In theory, they should be the same (for the principles of physics do not change). The angle between the tractor and the implement is the driver of force. The different approaches between John Deere and Kubota make no sense!

Does anyone have else have a manual for a different brand that they can reference?

Jack

 

[duroc]

Does anyone have else have a manual for a different brand that they can reference?
Jack

From my NH T1510 manual..

"The hydraulic lift rocker has two holes for attaching the upper link. Attach the link using the lower hole for light draft loads, such as mowers. Attach the link to the top hole for heavier draft loads, such as ground engaging equipment."

 

[94BULLITT]

From my jd 3720 manual:

• For light and medium draft loads: Install center link (A) in bottom hole (B) 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 (C) 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 (D) of mounting bracket. Example of very heavy draft load implements would include a plow or ripper.

That is what my Kubota manual says and my Bobcat manual also said that.

 

[Jack3489]

Roger, guess there is even a difference between Kubota models. My owner's manual for the L3800 says to use the bottom hole of the positioning bracket for "earthmover, digger, scraper and moldboard plows." It only says to use the top hole for "light soil" conditions. Appears to be totally contrary to your Kubota manual.

The mystery continues.

Jack

 

[94BULLITT]

Roger, guess there is even a difference between Kubota models. My owner's manual for the L3800 says to use the bottom hole of the positioning bracket for "earthmover, digger, scraper and moldboard plows." It only says to use the top hole for "light soil" conditions. Appears to be totally contrary to your Kubota manual.

The mystery continues.

Jack

I looked at the 4240 manual. I was wrong. Bottom holes for heavy draft work. I can't use the bottom hole. I usaully use the middle hole. My top link hits the PTO shield. Maybe I should remove for non PTO work.