how to build your own custom backhoe subframe

[dfkrug]

Not many tractor owners are willing to go thru the process of making a
custom subframe to mount a backhoe attachment securely to their tractor.
I want to encourage anyonewho is reasonably handy to consider doing
this....it is very rewarding, and you can endup with a TLB setup that
comes close to what you would get if you had a factory-integrated
Tractor-Loader-Backhoe. A custom subframe can be built BETTER than an
add-on subframe from a maker of hoe attachments. More on that later.

I get asked to build a subframe for someone else's tractor now and then. I
never take them up on the offer, but I am happy to show them how I do it.
I have helped some folks long distance, but that is difficult. I want to use
this thread as a go-to place for those considering the fabrication of their
own subframe. In my approach to design and fabrication, I always want to
have both the hoe and the tractor here: measure 3 or 5 times, and cut only
once, hopefully. I have learned a lot about backhoe attachments and
subframes by owning and making them, and by analyzing the many samples
I have seen. I have a large database of hoe attachment specs, but I
am always looking for more data and new ideas.

In this thread, I will show the process I went through to design and fabricate
a subframe to attach a Prairie Dog 7.5 backhoe attachment to a John deere
4300 tractor. I will use this and other examples of subframes to illustrate
different design approaches. Comments and questions are welcome.

But first, I want to discuss the basics.

What is a subframe? It is a structural member(s) that is rigidly tied
with welds, bolts, or pins to the main structure of the tractor. The
subframe rigidly transmits the forces from the implement to multiple parts
of the tractor's structure. By distributing the forces caused by the
implement, the tractor is protected from excessive concentrated forces, including excessive tension as well as destructive bending moments.

Subframes are used as a superior way to mount a backhoe, instead of
using the Three Point Hitch (TPH). There are many cases where a
Category 1 TPH has been used to successfully mount a backhoe.
There are also numerous documented cases where TPH-mounted hoes
have broken the toplink mounts, or cracked tractors in half. That is
no news to TBN members. Subframe-mounted hoes can also provide a
better integrated tractor with the hoe mounted much closer in to the
rear of the machine. A closer-mounted hoe will increase the minimum
departure angle, which is a fancy way of saying it won't hit the
ground as often when driving through a depression, or onto a trailer. Some
off-the-shelf subframes do not mount the hoe any closer than a TPH mount,
however. A closer-in hoe mount will also improve a tractor's drivability.
If a large weight it mounted far from the center of gravity of a tractor,
it will have what is called a high polar moment of inertia. This inertia
will resist changes in steering input.

In the first photo, I show the parts that comprise a 3PH hoe attachment
mechanism. On the left are the parts that are permanently bolted to the hoe.
The other parts comprise a much stiffer toplink, and brackets to keep the
lower 3PH arms (not shown) from rising. The second and third photos show
the same tractor on the 3PH, and on a Woods subframe, respectively. This
early Woods subframe does not mount the hoe any closer to the tractor
than the 3PH mount does.

Next: subframe types

[Robert_Parent]

Very interesting.. I look forward to the next chapter..

I would really like a small backhoe for my Kubota BX and have been giving much thought to building or modifying pieces of a purchased stand alone system.

Thanks,
Robert

[mmurphy]

I am going to watch with great interest. I have been thinking of ways to set up for my 416 Allis G.T... My first part will probably be a one arm loader, and then maybe a backhoe.

[D.James]

Very good info. I look forward to the next post.

Later
D.james

[magicheater]

I had the very same Prairie Dog Digger. A very quick and capable hoe with the pump unit they have. Sold it in pursuit of a larger unit.

[David Devuono]

I plan to add a subframe for my backhoe as well. I don't so much have a problem when digging as when I want to use the hoe to move the tractor around a bit. Thats when things get iffy and I wish I had a sub frame. thanks.

[dfkrug]

There are two major types of subframe used to mount backhoes to tractors:
The first I will call a ladder frame because it usually has two long beams
that go underneath the tractor (first drawing), connecting at the rear axles
or differential housing, and somewhere forward of the tractor's center. Some
form of toplink is usually required, too. My crude drawing is a side-view
schematic. Sometimes there are "rungs" on this type of subframe for more
structural stability.

The second major type of subframe avoids the use of the tractor's 3-pt
toplink in favor of four pinned or bolted attachment points. This requires
that the subframe wrap around the rear axle housings, so it must be
detachable in that area. These "Four Point" subframes are what you
will find on most modern CUTs and purpose-built TLBs. As a bonus, this
type of subframe is often very quick mounted/dismounted. This leaves half
or more of the subframe mounted to the tractor, even when the hoe is
removed. See the second drawing.

These 2 types could just as easily be distinguished at the "undermount"
type, and the "axle-surrounding" type. Some subframes are the latter
style, but don't use four detachable points. The point is the two categories
are not perfect.

[dfkrug]

There are some rather odd subframes that don't fit either of these
categories. I have seen subframes from deere for both the 955
and the 4300/4310 that are little more than small brackets that bolt
to the sides of the rear axle housings (photo). This approach has not
worked well, however, as JD later required users of their hoes to buy a
separate reinforcement subframe to add to that. I have posted a page
from JD's Subframe Installation Manual, which is dated 2005. That could
mean that this reinforcement was developed in response to failures
in the field. Like the one in the below photo. Here is a TBN thread
I posted about one of these broken JDs:
http://www.tractorbynet.com/forums/j...oken-half.html

The two small brackets are mounted using the same bolts that hold the
aluminum axle housings to the cast steel center gearcase. This has also
been a reported problem area. JD strongly advises users of backhoe
attachments on the JD4300/4310 to use the additional reinforcement.

This has not been much of an issue with the 955, since that tractor comes
with a full external frame, unlike most CUTs.

[jdmar]

I trust your knowledge and skills from your other posts...now you are scarring me! I have a 4300 with the 47 hoe on it. My tractor is not currently cracked in half and I would not like that situation to change. Do you know what part/kit# there is to add that subframe support to the tractor? Looks like it is smart insurance to me. I plan on keeping my tractor a long time. One thing I liked about this deere was the integral backhoe support that seemed to me (oops) to be stranger than many of the 3PTH models out there. I liked that you lifted with the 3PTH but then the actual weight was carried by the steel plates bolted to the tractor. Looks like this is why I am not a licensed engineer!

Peter

[arrabil]

Thanks dfkrug.