Hydro Pump Specs on Narrow Frames

[mkedzierski]

Hey,

Can anyone tell me the stock specs on the hydro pump used on the earlier narrow frames such as a 125? I'm trying to make a comparison to the BDU-10 used on the new new cubs. As far as I can tell, they were made by Sundstrand.

[R Bedell]

Cub Cadet used the Sundstrand 15U Pump. Just exactly what specs are you looking for...???

[J-Mech]

Since no one else seems to know......

If you are considering replacing the hydro in a 125 with a BDU-10, forget it. Linkage is different, pump is different. No, it isn't a Sundstand, it's a Hydro-Gear. Yes, it will bolt up to the rear, but the rest won't work without mods. Besides, it isn't near as good of a hydro as the U-15. The Sundstrand units almost never fail. If you have an issue with the hydro in the 125, ask some repair questions. Even if it is bad and needs replaced, there are usually 20 of the old Sundstrands on ebay for about $100. No comparing the two, they are very different internally.

[darkminion_17]

What he said times 2.
I think you would have to flip the big ring gear thingy in the twanny too.

[mkedzierski]

Originally Posted by R Bedell

Cub Cadet used the Sundstrand 15U Pump. Just exactly what specs are you looking for...???

I am looking for the torque specs, basically the overall "power" of the Sundstrand to compare it to a new cub with the BDU-10. What's confusing is a new cub has 22 to 25hp motor paired to the BDU-10 (compared to 10-14hp on older ones) so does this mean that the BDU-10 can actually handle 25hp (45 ft lbs torque estimate) and make it to the wheels? Not looking for opinions, but actual output data on the old sundstrand 15U.

[mkedzierski]

Originally Posted by J-Mech

Since no one else seems to know......

If you are considering replacing the hydro in a 125 with a BDU-10, forget it. Linkage is different, pump is different. No, it isn't a Sundstand, it's a Hydro-Gear. Yes, it will bolt up to the rear, but the rest won't work without mods. Besides, it isn't near as good of a hydro as the U-15. The Sundstrand units almost never fail. If you have an issue with the hydro in the 125, ask some repair questions. Even if it is bad and needs replaced, there are usually 20 of the old Sundstrands on ebay for about $100. No comparing the two, they are very different internally.

Thanks for the input. Not planning on switching, just need to compare the output torque to the BDU-10

[R Bedell]

Per the Sundstrand 15U Technical Manual

Garden Tractor – Vehicle with a 14 to 20 horsepower
(10.5 to 15 kW) gasoline or diesel engine that is used
as a mowing or utility vehicle. Capability for using
passive ground engaging implements such as mold-
board plows and front end loaders distinguish these
tractors from yard tractors. Tire diameters are typi-
cally 23 to 28 in. (584 to 711 mm) and vehicle weights
range from 1000 to 1200 lbs. (454 to 544 kg).

[J-Mech]

Originally Posted by mkedzierski

I am looking for the torque specs, basically the overall "power" of the Sundstrand to compare it to a new cub with the BDU-10. What's confusing is a new cub has 22 to 25hp motor paired to the BDU-10 (compared to 10-14hp on older ones) so does this mean that the BDU-10 can actually handle 25hp (45 ft lbs torque estimate) and make it to the wheels? Not looking for opinions, but actual output data on the old sundstrand 15U.

Originally Posted by mkedzierski

Thanks for the input. Not planning on switching, just need to compare the output torque to the BDU-10

I'll just give the short answer.

The BDU-10's overall efficiency, rated at 3000 RPM input, pump at full displacement caps out at about 180 lbf*in.

The U-15's overall efficiency, rated at 3300 RPM input, pump at full displacement caps out at about 500 lbf*in.

That is according to the Sauer Danfoss Series 70-15 pump book page 18 and 19. I have a PDF copy, but if you hunt around the internet, you'll find it.

Sauer Danfoss now owns Sundstrand and (did) help design the HG BDU pumps. I can't find anything that says that they still own HG.... and I'm not digging into it anymore.

By the way, if you would just look at the parts book for the BDU pump, you would see it only is a 5 piston pump/motor combo. The U-15 is a 9 piston pump/motor. Stands to reason it develops more torque without doing any math, or book searching.

[DoubleO7]

Originally Posted by J-Mech

The BDU-10's overall efficiency, rated at 3000 RPM input, pump at full displacement caps out at about 180 lbf*in.

The U-15's overall efficiency, rated at 3300 RPM input, pump at full displacement caps out at about 500 lbf*in.

Those are interesting numbers.

I don't know if those figures say the U-15 was used in way under powered tractors or the BDU-10 are used in way over powered tractors.

Or just that the U-15 can put out way more torque per hp input?

Still do not know why it takes twice or more hp today to do basically the same work that was done by 10 to 14hp years ago. Still running the same size decks and throwers (basically).
And I do not think there is as much demand today for ground engagement activities of these 20hp "lawn" tractors either.

[J-Mech]

HP is a function of speed only. Older engines tended to be large, with a big stroke, and put out a lot of torque. New engines while large, typically have a shorter stroke, and lower torque. Also, remember that when the old K series were built, there were no emission requirements. Emissions rob efficiency and power. Engines now are on the very edge of too lean. Things used to be far overbuilt, now things are under-built.... which is why they don't last as long, and why most newer engines are throw away. Another thing to consider is blade tip speed. It used to be a lot slower, and consequently didn't take the HP to turn. Another reason for higher HP....but again, I think newer engines are a bit overrated. Remember the 982? The Onan in it was rated at 19hp so that IH wasn't required to put a ROPS on the tractor. How much HP the engine actually made is debatable, but I'd say it was more like 22-25hp.

I'll say again, the obvious use of more pistons in the U-15 makes it able to produce more torque, but a hydro is very inefficient. Only 70-80% of the engine power can transmit through the hydro.