Top Link attach hole

[Bob_Young]

My Kubota L4300 has three holes; top, middle and bottom; where the 3-pt hitch toplink can be attached. I have position control only. The manual has little information on how to choose the proper hole, but there is a table that gives some guidance on tillage attachments. The middle and bottom holes seem to be favored for most everything. The top hole is only recommended for a mouldboard plow operating in 'light soil'.

When using my Woods HBL84-2 rear blade, I've found the toplink is closest to being level when the blade is in operating position when it is attached at the TOP hole. In the middle and bottom holes it's angled up toward the implement sharply (maybe that's the goal).

Anyway, using the top hole gives me more (useful) travel on my hydraulic toplink. In the middle hole, the toplink is nearly fully extended when I have the blade set the way I want. Adding Pat's EZ hitch to the lower lift arms complicated matters by moving everything further back.

What basic principles apply when choosing which hole on the tractor the toplink gets attached to? Does weight of the implement affect this decision? What about the height of the toplink attach point on the implement? Does the top hole have less mechanical advantage than the lower holes or put more stress on the tractor? Of the three, the top hole has the least attaching structure supporting it. Even the manual waffled a bit and said the table guidelines might not apply to all implements.
Bob

 

[inveresk]

The manual for my L3130 lists 3ph implements and which should be connected to each hole. These guidelines will have been prepared on the basis of using Kubota implements and all of mine are by other manufacturers. Accordingly, my 3ph attachments work best set differently to the recommendations Kubota makes. For example, I like my Buhler rfm and my box blade set in the top hole.

I would guess that Kubota makes different recommendations for your tractor but, for what it's worth, here are the recommendations Kubota makes for mine. These are straight out of the manual.

Moldboard plow - light soil 1 or 2; medium soil 2 or 3; heavy soil 3.
Disc plow - 2 or 3.
Harrow and subsoiler - 2 or 3.
Weeder/ridger - 3.
Earthmover, digger, scraper, manure fork, rear carrier - 3.
Mower - 3 for position control, 4 if draft control.

 

[3RRL]

Hi Bob,
That's an interesting question and I'd sure like to hear from others who REALLY know the answer.

Anyway, I'll give it a shot...
</font><font color="blue" class="small">( What basic principles apply...)</font>
I saw on your profile that you're and engineer (ret) so you probably got the "basic principles" thing figured out already. The lower holes in relationship, would seem to give more strength and sturdiness if you were to pull or push on that point (not suggesting you do that) because of their location...proximity to the axles and the rest of the hydraulic assembly casing.... more "connected" mass....more resistance to flexing and/or breaking, so to speak.
An example of the principle would be a flagpole solidly anchored in the ground. The farther up the pole you push or pull, the more it would flex or possibly break.

</font><font color="blue" class="small">( Does the top hole have less mechanical advantage than the lower holes or put more stress on the tractor? Does weight of the implement affect this decision? What about the height of the toplink attach point on the implement? )</font>
Taking all that into consideration...
I don't think there is MORE stress so much, but rather how the stress is absorbed better. If the toplink is angled, the load (push or pull) is deflected by a vector force. The greater the angle, more stress is applied to the toplink and its connections. It seems to me that the closer the top link is to level, the better the tractor absorbs the stress. (Assuming the connections are lower, closer to the base of the casting, like the earth securing the flagpole.) And the longer your toplink wil last.

With this in mind, when pulling your blade, resistance to the cutting edge at ground level will force it to pivot on the lower link pins, actually pushing the toplink into the casting, not pulling away from it, especially when going over. hitting a big rock. So it would appear the straighter that link is, the stronger it becomes, and the tractor can absorb that pressure. And because of this, I wouldn't worry so much about which hole to use for pulling your blade, but more for levelness of the toplink.

I also got Pat's EZ Change system and CCM's hydraulic Top & Tilt. When you adjust the tilt, you're basically rotating the implement around the same axis...the lower link pins. So the more leverage you give the TnT, the easier it is on it. I made two 1/2" thick brackets that allows the hydraulic clylinder to have equal travel in both directions and also a little more leverage over the implement. (See Attachment) It put the connection forward by about the same amount the EZ change system pushed it back.

 

[Toolguy]

The simple answer is that the lower holes will cause the 3PTH implement to lift higher at the rear when the lower links are raised. The top hole will allow a more level lift. Will it hurt anything if you use the top hole where the lower holes are recommended? I doubt it.

 

[Charolais]

If you're not using the draft feature it doesn't matter. Just connect to the hole that works best. For heavy tillage work like a bottom plow the draft is used. If you look around that area with the 3 holes I expect you'll see some type of linkage that operates the draft control.

 

[JerryG]

Charolais may be right about it not making any difference. The holes were actually put there to regulate the amount of force from draft that was put on the mechanical feed back for the draft control. The top hole for light draft and own down to the bottom hole for heavy draft.

 

[CT_Tree_Guy]

Bob - I chose the center hole for my rear grapple simply because I felt that would best spread the forces exerted on the gearcase over the widest area possible, and possibly reduce any "zipper effect" that might occur if, say, the top 2 bolts were to strip or break, then the middle two, then the bottom 2.

As for: <font color="blue">Does the top hole have less mechanical advantage than the lower holes or put more stress on the tractor? </font> It seems to me that using the top hole would (slightly) reduce the forces placed on the tractor, but then again, I agree with <font color="blue">Of the three, the top hole has the least attaching structure supporting it. </font>

So all in all, I just use the middle hole.

 

[Marlowe]

Good question. I don't know the official answer. What I've done is to experiment and find out which hole works best. The way I look at it, there are so many different attachments from so many different builders that the combination of possibilities is mind boggling, and therefore likely not covered in a list of standard recommendations. Trial and error works for me.

Good luck with it.

Tom

 

[wvhillbilly]

I keep mine in the center hole at all times for the exact reason Tree Guy stated. It seems to me that the overall mount would hold up better if all the forces and/or stresses were focused on the "center of the mount", putting equal stress on all 6 bolts that connect the top link bracket to the tractor. I have a K L3400 with NO draft control so that is obviously not an issue for me. The only ground-engaging implement I have thus far is a middle buster/sub soiler, and it works just fine in the center hole.

 

[RalphVa]

About the most important consideration is that the top link NEVER be longer than the lift arms. If you work out the geometry, with a too long top link, it'll make the lift arms want to tilt the implement towards the ground. There may be cases where you want this. Perhaps others can comment on this. You CERTAINLY don't want it with a brush hog. This is what happened when they delivered my brush hog. The top link was longer than the lift arms because they didn't mount the bottom pins on the brush hog to their lowest position. The lift would only move the front of the brush hog up about 1", whitch is all that was allowed in taking up the slack in the movable top link position on the brush hog.

Moving the lift pins down on the brush hog fixed the problem.

Ralph