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Well the BDU Pumps were first designed By Sundstrand. Sundstrand spun off it transmission for outdoor power equipment to Sauer Danfoss who In turn did a Joint venture with Agri-Fab to give the world Hydro-Gear

But here is a Manual with Both Pumps In it
 

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The Sundstrand Series15 hydros are rated to a peak pressure of 4500 psi and 2500 psi continuous duty pressure. In the unlikely case that traction can be found to require the continuous duty pressure, the final drive (rear end) is likely to break if it is a 2 speed in LO. There is no such concern with the BDU hydros.
 

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Interesting, so the BDU hydros arent bad?
The BDU Pumps are not bad hydro-static Pumps Hydro-gear has since replaced them with there P series pumps specifically the PG series replaced the BDU 10 series (y)
 

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The PW replaces the BDU 21 (y)
 

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So the BDU series pumps were commercial hydros?
@TUDOR can correct me if I'm wrong, but I suspect that he meant the BDU series is strong, but NOT strong enough to break the final drive like a Sundstrand 15U (like I did on my Legacy).
The Legacy is back in service, with a new-to-me Peerless 2600. One day, I'll find the time to finish the story on that one.
 

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Discussion Starter · #9 ·
I always thought the final drive breaks due to the amount of torque applied to the wheel but not being able to turn causing so much stress the final drive breaks. I guess maybe not. I have seen a couple of BDU series hydros in a 3000 series cub split in half from too much torque from the pump, then ultimately the case cracked.
 

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I always thought the final drive breaks due to the amount of torque applied to the wheel but not being able to turn causing so much stress the final drive breaks. I guess maybe not. I have seen a couple of BDU series hydros in a 3000 series cub split in half from too much torque from the pump, then ultimately the case cracked.
The BDU-21s are really strong. The only thing I have seen them break is the gerotor.

The rear differential they are bolted to is famous for having ring/spur gear bolts with no loctite on them. They back out and then the differential breaks from a bolt hanging out. This was on the cast iron with diff lock rears.

I've had a 3000 series with cast iron rear and alum rear torn down. Another weakness is the spur gear flakes the coating off and gets rough. The metal accumulates on the bottom of the case.
 

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I always thought the final drive breaks due to the amount of torque applied to the wheel but not being able to turn causing so much stress the final drive breaks.
That's correct and this is precisely what happened to mine: Unable to break loose a buried railroad tie, and getting great traction in low gear, something had to give. In my case, the Sundstrand twisted the axle into two pieces, with the splined stub left in the differential.
 

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@TUDOR can correct me if I'm wrong, but I suspect that he meant the BDU series is strong, but NOT strong enough to break the final drive like a Sundstrand 15U (like I did on my Legacy).
The Legacy is back in service, with a new-to-me Peerless 2600. One day, I'll find the time to finish the story on that one.
Yes, the BDU series makes for strong hydros, but they are consumer grade as opposed to the commercial/industrial grade of the Sundstrand Series 15 hydros..

The specs for both are on pp 6 (BDU) and 7 (Sundstrand) of the manual attached by Sergeant above. By plugging the numbers into the simple formulae available online, the relevant horsepower and torque ratings can be calculated for comparison. The one spec that tells the story is the weight of the hydro. The BDU-21 weighs 23 lb and the Sundstrand with a smaller displacement, but of the same basic design, weighs 33 lb.

That manual is a great read if you have an interest in hydros, It explains a lot of the 'secrets' that go into a hydro's capabilities. I seem to learn a little bit more every time that I get into it. Just don't try to absorb it all in one reading. Information overload takes on a whole different meaning.
 

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That's correct and this is precisely what happened to mine: Unable to break loose a buried railroad tie, and getting great traction in low gear, something had to give. In my case, the Sundstrand twisted the axle into two pieces, with the splined stub left in the differential.
When I blew up my Peerless 2500 2-speed final drive, the gears and axles were fine. The forged bolts holding the differential together blew apart. The nuts and threaded ends were on the bottom of the sump, and the head ends were chewing up the case. It operated like that all winter and didn't indicate a problem until the next spring when I was tilling and the filter plugged up.

Maximum axle torque rating for the Peerless final drives is 1200 lb-ft.
 
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So are the BDU10‘s not strong then? I know for a fact the one in my gt2544 is very strong and fast.
The BDU10 and 21 operate at 1000psi but the 21 has double the pump and motor displacement. However the torque multiplication thru the differential makes the available torque at the tires closer than that would indicate. My BDU10 will pull a box blade just fine.

The differentials are the same, just the transmissions are different. My 10 feels 70% as strong as the 21s
 

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A bit of Info on a Cub Cadet competitor using BDU Pumps



These Deere Garden tractors used BDU 21 Pumps on their Belt driven Hydrostatic Transmissions

245, 265, 285 and 320



These Deere Lawn tractors used BDU 10 Pumps on their Belt driven Hydrostatic Transmissions

111H, 112L, 116H, 165, 175 and 185

(y)
 
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Discussion Starter · #18 ·
A bit of Info on a Cub Cadet competitor using BDU Pumps



These Deere Garden tractors used BDU 21 Pumps on their Belt driven Hydrostatic Transmissions

245, 265, 285 and 320



These Deere Lawn tractors used BDU 10 Pumps on their Belt driven Hydrostatic Transmissions

111H, 112L, 116H, 165, 175 and 185

(y)
Ok you tell me if im wrong, but the BDU10 is a lawn tractor hydro pump, and the BDU21 is a garden tractor hydro pump? So then the 2500 series and successors are all lawn tractors with garden tractor wheels, frames, engines?
 

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Discussion Starter · #19 ·
Also, the john deeres that used the BDU10 used the s model instead of the L model. L model is stronger. Also i did The calculations for the hydro in my cub (BDU10L) and it came out at 626.5 footpounds of torque with the gear reduction of the transaxle.
 

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Discussion Starter · #20 ·
Yes, the BDU series makes for strong hydros, but they are consumer grade as opposed to the commercial/industrial grade of the Sundstrand Series 15 hydros..

The specs for both are on pp 6 (BDU) and 7 (Sundstrand) of the manual attached by Sergeant above. By plugging the numbers into the simple formulae available online, the relevant horsepower and torque ratings can be calculated for comparison. The one spec that tells the story is the weight of the hydro. The BDU-21 weighs 23 lb and the Sundstrand with a smaller displacement, but of the same basic design, weighs 33 lb.

That manual is a great read if you have an interest in hydros, It explains a lot of the 'secrets' that go into a hydro's capabilities. I seem to learn a little bit more every time that I get into it. Just don't try to absorb it all in one reading. Information overload takes on a whole different meaning.
I dont know if the BDUs arent ”commercial“, they are used in lots of commercial application.
 
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