Backhoe attachment, on a trailer. Making it a towable!

[4570Man]

You can get by with a much smaller motor probably 5 gmp at 2500 psi would be adequate. The biggest problem I see is weight and cost. You’re going to have to add considerable ballast to make this thing something that resembles useful. Second problem is the resale value of this will be very low. The resale value of a used machine that was bought right is near 100%.

 

[4570Man]

I don’t know what your budget is, but I doubt you can pull this off for less than $5k. That would go a long ways toward an existing machine.

 

[BrokenTrack]

I don稚 know what your budget is, but I doubt you can pull this off for less than $5k. That would go a long ways toward an existing machine.

I disagree, I think a person could build a towable backhoe for well less than $5,000.

I might consider buying a woodsplitter. A decent one costs $750 and would net a person an engine, hydraulic tank, pump and one cylinder. From that a person would just need to buy 3 more hydraulic cylinders at a few hundred a piece, a 4 valve stack from Supply Center for a few hundred bucks, hoses to connect it all, then some steel to make the machine. It would be hard to give an exact figure, but I figure between $2500-$3000 to build one. Making it yourself though would enable a person to have a more capable machine.

There is something to be said for just going out and renting a machine because $3000 would get a lot of digging days out of a rented machine, but what I have found is, having a small backhoe around allows me to do the little jobs that are too big for a shovel, and yet too small for anyone else to want to come in and do.

The other thing too is, when you get attachments, you use them for a ton of stuff you never initially envisioned just because you have it.

 

[4570Man]

The op was wanting to buy a tractor backhoe and convert it to trailer mounted. I don’t see any backhoes that have potential to work again for less than $2500. The op might find a cheaper one. $2500 more to get a trailer, and the rest of the hydraulics seems reasonable.

 

[Gary Fowler]

Call me lazy , but this is what I would do. It has stabilizers to hold it in position (unlike the $3000 one) and it can move itself around. When finished just hook it to your tow vehicle and take off.

14.5 FPT Towable Backhoe | DR Power Equipment

 

[Groo]

If you are buying a used backhoe attachment initially intended for one specific machine, match the pressure (less will drop your digging force, more could easily damage something) of the hydraulics it was intended for and go with less flow than the base machine intended. The toe behind wont have the weight of a tractor on it to keep it from jumping around, so you will want to go slower for a bit of reduced violence.
on a budget, you will definitely want open centered hydraulics, because closed centered hydraulics pretty much require a variable displacement pump, and those are much more expensive than a cheap gear pump.
Once you have a flow number you want to hit, you can calculate the pump size based on that and the engine RPM (usually 3600rpm for small stationary engine like a Briggs or cheap Chinese Honda knock-off). once you have pump size and pressure, you can find torque requirements pretty easy.
here are the pertinent calculators;
Hydraulic Motor Calculations - Womack Machine Supply Company

here is an example on choosing pump and engine;
lets say you want 2000 psi and 7 gpm.
a .5 cu-in/rev pump will give you a bit over 7 gpm at 3600rpm, so lets go with that.
here is a fairly cheap .55 cu-in rev pump that can be spun to 5000rpm and can handle 3480 psi; so that will give us a generous cushion and the pump should actually last quite well in this application.
Hydraulic Pumps | Gear Pumps | Dynamic Hydraulic Gear Pump �.55 cu.in/rev | B537177 - GlobalIndustrial.com

.55cu-in/rev needs to only spin 2940rpm to make the desired flow.

.55cu-in/rev @ 2000 psi needs 175 in-lbs or 14.6 ft-lbs.

the harbor freight 8hp engine makes 14.9 ft-lbs peak at somewhere near 2500rpm, so that would be a great match for this combo when driven directly.
8 HP (31cc) OHV Horizontal Shaft Gas Engine EPA

this combo would cost $230 for the engine and $95 for the pump, plus whatever you need to splice the two together.
another possible solution would be to use a go-cart clutch and chain to attach to two. since you would get a gear reduction when doing that, you would need a larger pump, but don't get a gear pump that would be spinning less than 900 rpm when running. they loose efficiency going too slow.
you might do a belt drive and could gear up or gear down the pump. if you speed it up, you can use a smaller cheaper pump. Just be sure you don't spin the pump faster than it is rated for at full engine speed.

ETA. don't forget filtration!

 

[texasranger556]

Its differs a lot by area. I see skid steer backhoe attachments on Craigslist in the $2000-2500 range fairly often. There is a bush hog 962 listed for $2k right now that looks in good shape but has some leaks.

 

[Reg]

Back hoes, excavators and similar devices are able to do the work that they can do largely because they have MASS against which the bucket can pull/push.

Mounting something on a trailer would put it on (relatively) squishy wheels and you would find them flexing as they absorb some of the force - then letting go when what you are digging into comes loose.
Don't count on the mass of the tow vehicle to help you out, the trailer is is attached by a hinge - a 3D hinge (ball/coupler) at that.

 

[Groo]

Back hoes, excavators and similar devices are able to do the work that they can do largely because they have MASS against which the bucket can pull/push.

Mounting something on a trailer would put it on (relatively) squishy wheels and you would find them flexing as they absorb some of the force - then letting go when what you are digging into comes loose.
Don't count on the mass of the tow vehicle to help you out, the trailer is is attached by a hinge - a 3D hinge (ball/coupler) at that.

a backhoe attachment likely has outriggers, so the back will be solid. If its got a decent sized tongue it would have loads of leverage against the ball. it could be easily useful. Like I said, I'd just go a bit slower with it.

 

[BrokenTrack]

This is more in line what I was thinking about. I still do not see more then $3000 in it, and other than the bucket curl cylinder being too short, it is a lot more capable then my Wallenstein Log Loader Backhoe because it can go deeper. The video also shows how two wheel towable machines can be moved on their own power.

Don't get me wrong, this is no Hitachi 1200, but for the money, and ease of build, I think its a very decent machine. I think if someone spent $3000 building it, they would be happy versus that of having a spade and pick axe.