The pump mounted behind the hydro must be small, about 3.25 inches square to fit, and it's a snug fit.

There are several pumps in this series with same dimensions. My pump was a .129 cu in. displacement, which provides 2 gpm at 3600 rpm. That's all I needed for my single cylinder, dumping the bed and gave a moderate cylinder operating speed.

You'll want a larger displacement pump, perhaps the one with .258 cu in displacement, giving 4 gpm at 3600 rpm.

The larger displacement pumps in this series are limited to 2500 rpm intermittent. Download the tech data from Northern's web site for the pump linked below, and you'll see the pumps in the series.

Here's a pump that might work for a loader--
https://www.northerntool.com/shop/to...9708_200329708

Four gpm might be a bit slow for a loader, depending on the size of the cylinders. This is a high pressure pump, 2300 psi continuous, so you could use smaller diameter cylinders, giving a bit more speed on operation.

As you design the loader, you'll need to take into account pump pressure, flow rate, cylinder dia and length, and lift and curl geometry. All those things determine functionality of the final design.

Remember that hydraulic cylinders often use very high force on a shorter moment arm to achieve greater movement at the end of the component. In other words, a cylinder that pushes at a point 1/3 the way down a beam, and lifts it 1 foot with 1000 lbs of force can lift 333 lbs, 3 feet high at the end of the beam. So the lever fulcrum location and length of the beam determine the forces needed to lift a given weight.

Archimedes said it all--"Give me a lever long enough and a place to stand and I can move the world."

If you decide 4 gpm is marginal in terms of capacity (as it might be) then you can use a larger pump and mount it differently--either further back behind the rear end, where a larger pump might fit, via a belt above the hydro unit's rear output, off the front PTO (as I suspect most are).

I'd try to contact the guy who built the loader just linked a couple posts back (where I got the idea to mount my pump) and ask him what pump he used and was he happy with the loader operating speed and capacity.

Be sure to look closely at the pump's rated RPMs as many are not rated at the Cub's engine speed--3600 rpm.

Lots of stuff to digest.

all VERY helpful thanks! yes I understand about the geometry but I did wonder why some have such a leverage disadvantage. one aspect u didnt mention is lets say I can find a 3600 rpm capable pump with lots of GPM, at what point is that too much for the 12hp Kohler?

As to choosing a pump too big for behind the hydro pump (I could cut-weld some mods tho), I wonder if theres a front PTO option that has a full time pulley behind the switched pto pulley...

or just run it off a pulley on the back of the engine like IH did... definitely dont want to skimp on bucket speed or lifting power tho...

Lots of factors affect HP requirements for hydraulic pumps including temperature (and viscosity) of fluid, plumbing friction losses, pump efficiency, etc. But you can approximate your requirements with these two equations.

this is a common rule of thumb equation:

HP=GPM x PSI x .0007

So 6 gpm x 2500 psi x .0007 = 10.5 HP

Or, another equation sometimes used,

GPM x PSI/1714 = HP

Gives a slightly different answer, 6 x 2500/1714 = 8.75HP

I think the answer to your question is a 10, 12 or 14hp Cub Cadet can easily drive a decent loader at reasonable speed.

For reference, my Kubota BX23's pump is 6 gpm at (I think)2500 psi, and the loader and backhoe work fine.

One more thing, since you mentioned lifting power. You are limited by the weight of your tractor, so adding rear weight may be needed, which, unfortunately, does add wear on rear axle bearings (unless all the weight is in the tires/wheel weights.)

Thanks sawdust, very cool info. Now I could do the calcs but the 6gpm at 2500 seems more than adequate and will use less power than the engine has. I'm sure that tractive power needs wouldnt happen at the same time as loaded bucket movement (?)

You did touch on something else new to me, the rear bearings. I always assumed that since that rear is adapted from a farmall cub, has plenty reserve strength but the axle housings may (probably) be made for cadet and have less stout bearings. I'd have to look up both and see.

I asked a foundry for a quote on a custom cast iron weight about 14x14x7 which should weight about 600lbs or close to it. The weight of the tractor, operator, and the extra weight out back are all behind the front axle, where the loader itself plus the load (500lb max) are out front by 4ft or so.

does any of this make sense?

A small loader bucket of gravel weighs about 700 lbs I think. +/-

I'd install a rack and add smaller incremental weights as needed. Handling a single 600 lb chunk of iron could be problematic. Might drop in on your toes. LOL.

LOL yeah. The foundry wants $850 for that piece and interestingly he said 410lbs but at 705lbs per cu ft for cast iron, I did the math should be ~600lbs. But anyway. Too much $$$

Still wondering about those rear wheel bearings. The front will be upgraded to 1" spindles w 5 bolt hubs and wheels. (spindles and hubs is on the way but lost in limbo by the USPS!). I dont think the front pivot pin will be an issue but if it causes any problem I'll beef that up too.

BTW I am famous for getting off to a quick start then taking a year or two to finish... but this will be finished! Tractor will be running in a few weeks hopefully with the cheapo agrifab plow I just got off FB. The lowder will take a lot longer to build and pay for the materials....

I have a friend out west who has built I think 2 loaders and 3 backhoes for small tractors, and has some great tips for it all.

I would not worry too much about the rear axle bearings. They are actually pretty durable, as most last 50 years or more. Easy to replace if needed.

If you have the rear end cover off to change the fluid, pull the circlips (E clips) off the axle ends, slide them out, replace the needle bearing and the oil seals on the end of each axle housing. Put the axles back in and replace the clips, button things up. You're good to go for another 50 years.

With an extra 500 lbs hanging off the back of the tractor, the bearings might only last 20 years...