3-Point Hitch 3 Point Lift Capacity Question

[GreenTime]

So my JD 3720 has a rated lift capacity of 2,530 lbs according to tractordata.com. So does anyone know if a tractor's 3 point has the most lift capacity at the very bottom or very top of its lift range? I am building a hitch to lift a 5th wheel camper (2,200 lb pin weight empty) and I just want to lift it just off the ground and move is a short distance. Depending on how I design the hitch, I can lift at the bottom or top of the 3 Point lift arc. Thanks.

 

[farmeratheart]

To me the “strongest” point would be when the lift arms were parallel to the ground. I’m sure there will be other opinions!

 

[hosspuller]

Be aware that having the hitch point above the rear axle could flip your tractor in a backward somersault. The lower you carry it above the axle, the better. Front weights or a FEL help too.

 

[i7win7]

Here is one from TSC
CountyLine Trailer Mover at Tractor Supply Co.

Here's how I modded mine with Harbor Freight accessories. Think the winch mounting bracket was for a kawasaki mule. (lack welding skills)

 

[ruffdog]

If you want the most capacity, make the frame so the ball is closer to the tractor. The further away from the tractor, the less weight the arms can lift.

 

[LD1]

Work out the geometry so that the ball stays straight when lifted.

That means that where the toplink hooks up to your attachment will be LOWER than normal.

Because the way the 3PH is designed currently, and most implements.....when you raise....the tail of the implement (think tailwheel of a bush hog) raises MORE than the front. Its intentional to give it pitch to clear the ground when crossing uneven terrain or loading on a trailer.

All of which is not needed for a trailer mover. So if you make it stay exactly vertical through out its range, it actually wont loose any lift capacity getting further away from the tractor. BUT.....it will take more weight off the front axle, and since you are pushing max anyway, keeping it as close as you can would be best.

But there is no easy answer to your question because there are too many variables from tractor to tractor. But in general, the highest and the lowest points will yield the most lift force. Because the arms are traveling in an arc (which is just a "part" of a circle.)

So when you think about it like that, when the arms are perfectly parallel to the ground, is when it requires the most force to lift something.

AS you near the top of the travel, you are not lifting straight. ITs actually lifting and moving closer to the tractor.

In otherwords.......when the arms are straight parallel.....and you raise the hitch 6"....you are effectively lifting the trailer ~6".

When you are near the top of travel, and you raise 6"......you might only be raising the trailer 4" and 2" forward. So as things relate to gravity, with the same movement of the hydraulics, you are actually doing less work. IE: greater mechanical advantage.

Usually its not significant enough to worry about because its splitting hairs. But that sounds like what you need nearing maximum rating.

So, in a nutshell, I'd shoot for the upper rage of your travel. Because the combination of it moving the lift point as close to the tractor as it can, as well as a slight capacity increase, is gonna be your best bet for success. But I'd keep the jack on the trailer pretty close to the ground as it will sorta act like a wheelie bar.

And a front loader or front weights is a must lifting that kind of weight with such a small tractor....

 

[Sawyer Rob]

So my JD 3720 has a rated lift capacity of 2,530 lbs according to tractordata.com. So does anyone know if a tractor's 3 point has the most lift capacity at the very bottom or very top of its lift range?
Thanks.

None of that matters, once the front end comes off the ground!

SR

 

[GreenTime]

Most replies make some good points. I plan to have sufficient front ballast to keep the front tires on the ground.

I think another factor is the geometry of the internal hydraulic 3 Point Cylinder and when it pushes perpendicular to the lever arm at it longest point in relation to the center-line of the rockshaft. I've never had one apart so I am not familiar with the geometry.

 

[EarPlug]

The lift rating of 2,530 lbs is at the "end of the arms". If you are attempting to design something that going to effectively extend the length of the arms you will need exponentially more lift capacity.

This is just like front loader specs. Lift capacity is measured "at the pins".

 

[LD1]

The lift rating of 2,530 lbs is at the "end of the arms". If you are attempting to design something that going to effectively extend the length of the arms you will need exponentially more lift capacity.

This is just like front loader specs. Lift capacity is measured "at the pins".

It's not at all like a loader.

Loader is pretty much simple leverage.

3ph is not. And in fact if you do as I mention and keep the lift parallel....like I have also done with my 3ph pallet forks by lowering the point where the toplink attaches....my lift capacity is the same at the heal of the fork as it is at the tip of the fork