3 point backhoe

[currierej]

I just bought a 3pt backhoe, it has a homemade bobcat QD, and I'll be converting it to a 3pt style hookup.
The hydraulics are setup for a bobcat, but I will be using a pto pump with a small tank.
Does it matter if the tank is mounted lower, higher or at the same level as the pump?

 

[George2615]

I have a Woods BH750 with sub frame and the tank is level with the pump.
I would suggest you build a sub frame to attach the BH to the tractor. I've never seen one but I have read of people breaking compact tractors using it just on the 3 pt. There are some that say it will work fine but I think a BH puts a lot of stress on the tractor, especially on the top link.

 

[Tomtint]

There are threads here about 3PH backhoes. .. I have a L3700SU and my BH77 will throw the tractor around if I'm not careful...don't think I would want that stress on a 3PH alone.

 

[flingwing1969]

There are threads here about 3PH backhoes. .. I have a L3700SU and my BH77 will throw the tractor around if I'm not careful...don't think I would want that stress on a 3PH alone.

I have no experience with a TPH hoe, mine have always come from the factory with sub-frames - Kubota B-21 and LS 3038H. I kind of figure if it's good enough for the factory . . . Check out this post on how to build one by my friend DFKrug. He used to sell Prairie Dog TPH hoes but always with a subframe he build custom for each job.

 

[currierej]

I think that I have decided to build a subframe, if I attach it to the FEL brackets and to some brackets by the rear axle would I still want to attach to the top link?

 

[currierej]

Also, would 4"×4" heavy wall square tubing be over kill, just right, or too weak?

 

[flingwing1969]

Also, would 4"×4" heavy wall square tubing be over kill, just right, or too weak?

I think 4x4s are an overkill the factory subframe on my LS uses 2x4 (I think, the snow on it is deeper than I want to hassle with right now) I'll take a picture of it for you. The LS is a ladder type and it connects at the front of the tractor with very simple slide in brackets and at the back with an open box into which the aft-most cross member of the subframe fits - held in place with two drop pins. It does not connect at all to the FEL towers.

Here is what it looks like. I find that it is very stable, does not move around and does not seem to put too much stress on any of the tractor parts, including on the top link, which it uses.



My B21 had a permanently mounted subframe with a heavy mounting bracket on the back similar to a TPH quick attach system but it mounted the hoe very close to the tractor so that the swiveling seat could be used for tractor and for hoe work - it was convenient but I do like the LS style a bit better and it is slightly quicker in the on/off operations.

 

[dfkrug]

I think that I have decided to build a subframe, if I attach it to the FEL brackets
and to some brackets by the rear axle would I still want to attach to the top link?

It is there and strong. Why not use it? My own personal hoe, which has served me well for that past dozen
years, connects to FIVE points on the back of the tractor-side subframe. I still get a bit of flex.

In choosing the steel for the main structural member of your subframe under the hoe, there are several
factors to consider: do I have some steel already that I do not have to buy? Great if you can reuse
some steel that you salvaged, or already bought in bulk.

If you have purchased nothing so far, then a round-cross-section tube will be the strongest in all
directions, per unit pound. Since you are concerned about up-down strength, not left-right, a deep-
section beam is better usable strength per unit of weight. I-beams are ideal for this kind of strength, but
not ideal to weld to, on the sides. The best shape compromise is a C-channel with thick web. This is strong,
easy to weld to on one side, and commonly available.

If you look at OEM designs, the good examples use solid plate, often as much as 3/4" thick. That
material is easier to machine in a factory setting, IMO, and weld to, if you have to weld both sides. It
will weigh and cost a lot more than channel, however. You and I may struggle with the weight of
3/4" plate, but the factory likely does not.

 

[flingwing1969]

I really suggest you read the thread I shared. Dave is a remarkable fabricator and he is a CE so everything he does is well thought out. It is a long thread but I know if I was going to build a subframe I would read it all as there is much to consider. It is really not a difficult fabrication job but the thinking must be well done and Dave has done much of it already.

 

[flingwing1969]

Here is another drawing of the subframe assy on my hoe/tractor showing better how the various parts interact.