Newbie needs 3pt hitch advice

[Bob_Trevithick]

Hi Gang,

I just hooked up my first rear attachment on my 4300, a King Kutter 30" dirt scoop, and everything went well. Most of it was pretty obvious, but there's one thing I'm not clear about.

In the tractor manual, it mentions the three positions that the tractor end of the top link can be mounted in; the bottom one for light loads, the middle for medium to heavy loads, and the top one for very heavy loads. I experimented a bit with the top and bottom mount position, but it wasn't obvious to me, at least with just the scoop attached, why one would use anything but the position for heaviest loads.

I'm sure there's a reason.. but this is one of those cases where the tractor manual tells me how to do something, but not why I might want to do it. The manual assumes some knowledge on my part, and it makes too charitable an assumption. /w3tcompact/icons/smile.gif

In short, what are the advantages of using either of the other two positions?

TIA,
Bob

Bob Trevithick

 

[rf33]

I think that the trade off must be weight vs. range of motion. i.e. In the light implement setting, I think that you can lift your implement higher than you can in either of the other two.

rf33

/w3tcompact/icons/wink.gif

 

[Bob_Trevithick]

Yeah, that makes sense. Just from the standpoint of geometry, I guess that would be the only possible trade-off. I'll leave it on the heavy position until I find myself needing to lift something higher, and then experiment some more.

Thanks for the advice!

Bob Trevithick

 

[rf33]

I am not real sure about that, just a semi-educated guess as to why the multiple positions. It makes sense to me that that would be the trade-off, but hopefully JMIII or one of the other experts would give an authoritative answer. The more I learn, the less I realize that I know.

rf33

/w3tcompact/icons/wink.gif

 

[Estif]

I'm not one of those experts, but I figured I could do my part to add to the confusion.

Mine has four possible positions for the top link, and the manual indicates that the third from the top would be used with plows, so I use that for my middle buster. And I use the top position for everything else - which includes a box blade and post hole digger to date. I had the idea - don't know where I got this idea, BUT - I had the idea that it wasn't an issue of weight so much, because weight goes on the lift arms. But putting the top link in different positions changes the geometry of the hitch in such a way that the "angle of attack" of the implement throughout the range of travel is affected. Wow. That statement's not even clear to me, right now, and I don't know how to make it clearer without drawing pictures. Let's see. For a given lift position, changing the length of the top link changes the angle of the implement - lengthening the top link tilts it back, shortening tilts it forward. But that angle also changes as I raise and lower the implement. For example, if I set the top link to make my box blade level, front to back, with the box on the ground, then the box will tilt back as I raise it. I think. The computer's in here, and the tractor's out there. But I think the way that angle changes as the implement moves up and down changes when the top link's in different positions.

Another guess on why different positions are used - I notice when using the middle buster that when the top link is in lower position, the link is more in compression (stronger) and less in shear than when the link is in the higher positions.

That's two guesses. I will now take my seat and wait with the rest of the class for revelation from the sage.

Steve

 

[RobS]

The tph is a classic four bar linkage studied ad-nauseum in mechanical engineering (which I've long since forgotten). The tractor is one bar (from arm pivots to top link pivot), the lower arm is a bar, the implement is a bar (from lower pins to top link) and the top link itself is a bar. Changing the top link on the tractor changes the geometry of the whole arrangement and probably affects lift height, lift capacity and arc of the implement. (BTW, the rockshaft and lift links are a completely seperate quasi-four bar linkage)

Think of a square with one vertical leg the tractor. Being a perfect square, if you lift the opposite leg it will remain parallel to the fixed leg. If you shorten one leg, the outer will no longer remain parallel as it moves.

I'd have to refer back to my old books to figure out what this really means on a tractor. Sorry, but it's my last day of work this year and it's way to early in the morning for that kind of brain excercise /w3tcompact/icons/smile.gif

 

[Anonymous Poster]

I don't know if a 4300 has draft control on the 3 point hitch, but that would be a very good reason for different top link connection points. This would be used to adjust the amount of draft feedback to the hydraulics, with heavy loads providing less feedback than light ones.

 

[Bob_Trevithick]

<font color=blue>...I don't know if a 4300 has draft control on the 3 point hitch, but that would be a very good reason for different top link connection points.</font color=blue>

Hmm. I have "draft links." I see no mention of "draft control." I need to do some more reading to find out about this draft control, but as far as I can see so far I don't have it.

I'm guessing this is come kind of feedback mechanism to keep ground-engaged implements at a constant depth?

Thanks,
Bob

Bob Trevithick

 

[Redsmoke]

Bob, That's exactly what it is. The old Ford 8N tractors had draft control. The JD 4300 doesn't. I just use whatever hole is the handiest when I hook up an implement, usually the middle one. My post-hole digger has to be hooked on the top hole. As far as figuring out the geometry of it all, it just takes too much energy LOL.

 

[Egon]

Bob:
Estif should have it right in his first assumption. Alters the angle of attack.
Egon