# Hydraulic PTO Pump Somehow Sheared Off the Tractor's PTO Stub Shaft



## SHEF (4 mo ago)

Hello, I'm a new member (was a reader before I was a contributor). I have a 27 acre farm in New York State and we have a MF 1735E tractor. We got a BH7 backhoe (3 point attached with a hydraulic PTO pump). 

On the first real test of the backhoe digging a simple hole to practice the PTO Stub Shaft shown in the photograph completely sheared off the tractor. I had to remove it from the Hydraulic Pump which was just hanging by the two secure chains at that point (and the hydraulic hoses still attached to the backhoe). The only damage was to the stub shaft, nothing else broke or was affected. 
Now the tractor has been fixed and the BH7 and pump are mounted back on the tractor but I'm not the type of person to make the same mistake twice. I followed the instructions with regards to the chains to have them loose enough to not restrict the pump but tight enough not to let the pump rotationally turn too far. Is there a special hitch that can better mount or secure the pump so it's not just dangling in space by two loose chains?

I'm operating under the assumption that if this happened to me then it must have happened to someone else at some point. Everyone who lives near me who works in construction who I spoke to said they'd never seen anything like it. I appreciate any and all help. Thanks a lot.


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## BigT (Sep 15, 2014)

Howdy SHEF, welcome to the tractor forum.

Yes, we have had this happen before. See attached thread:








Attaching PTO Hydraulic Pump


HI Folks, I will be hauling my Nortrac 25XT to a Northern Tool Mechanic about 80 miles from here this morning to replace a sheared off PTO Shaft. The question is when replaced I will have to attach my PTO Pump back on the shaft, and certainly don't want it to break again. So what is the best way...




www.tractorforum.com


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## SHEF (4 mo ago)

Thanks so much for that link. I just wrote the originator of that post to see how he ultimately solved it and if the solution was a success. My takeaway from that discussion was that the mounting chains that come with the pump have to be loose enough not to restrict the pump from moving but tight enough to not allow the pump to go spinning around. I searched the manual for the backhoe for any advice and it didn't have any to give. I also wrote the vendor who sold the backhoe (he's a pretty personable guy, we've spoken before) to see if he has any tricks up his sleeve.


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## thedukes (Jan 9, 2022)

That is a bizare break
Not one I'd ever guess to happen.
You have me quite curious now as to the cause.


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## SHEF (4 mo ago)

This is how we mounted the PTO pump to best copy the image provided in the manual:


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## BigT (Sep 15, 2014)

See attached instructions for connection of a Prince PTO pump to tractor. The pump sits freely on the PTO shaft. The pump has a lever arm that chain attaches to to prevent the pump body from rotating as as the PTO shaft drives it internally.



https://www.northerntool.com/images/downloads/manuals/1051.pdf


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## LouNY (Dec 15, 2016)

I have had the same issue on a IH 574. I blamed it on having to run a stub shaft to clear the dual pto's on that tractor.
We have run similar pumps on other tractors for 100's of hours, the Heston haybine was powered hydraulically from a large pump that hung off the pto with no issues
on other tractors. I would say to check for hoses pulling on the pump at different heights that you may acquire while using the hoe.
I would prefer a remote mount with a short pto shaft.


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## SHEF (4 mo ago)

LouNY said:


> I would say to check for hoses pulling on the pump at different heights that you may acquire while using the hoe.
> I would prefer a remote mount with a short pto shaft.


I just took these photos thinking about what the hoses do as the unit is spun up. It made me wonder if we mounted it upside down, but I'm certain that the reason we choose this way is it was less manipulation on the hoses and the writing on the box was Face Up. In one photo you can see where the hydraulic hose will catch the pump as it is inclined to spin away from the viewer and the hose will strain against the blue support beam preventing the pump from spinning. 
It's possible to attempt to restrain that hose away from the support beam but that would just mean the pump would pull the hose and then pull at the restraint as it attempted to spin.


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## LouNY (Dec 15, 2016)

Our pumps had an arm that stuck out to catch against the drawbar to prevent rotation and some had a chain also. We usually chained to the lift arm
with the safety chain. Is your backhoe mounted on the lift arms?
When you put down your out riggers to dig is it lifting the hoe higher and causing any binding?
When digging and working is the hoe moving around a lot to cause binding and pulling on the pump lines?


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## SHEF (4 mo ago)

LouNY said:


> Our pumps had an arm that stuck out to catch against the drawbar to prevent rotation and some had a chain also. We usually chained to the lift arm
> with the safety chain. Is your backhoe mounted on the lift arms?
> When you put down your out riggers to dig is it lifting the hoe higher and causing any binding?
> When digging and working is the hoe moving around a lot to cause binding and pulling on the pump lines?


The backhoe is mounted on the lift arms, you can see the mount in these new photos that are from further away.
When the out riggers are down I did not lift the tractor off the ground and didn't significantly lift the backhoe. I lowered the arms to a low setting for a low center of gravity for the backhoe. There wouldn't be any way in the current configuration for any binding that didn't involve the hydraulic hoses themselves which you can see slightly toughing the blue stabilizing arm. 
When digging there was the upward jerky movement that comes from force transmitting through the hoe and backward along the tractor (I was expecting that from all the videos I watched). The way it's attached now the chains are wrapped around the PTO guard which wouldn't in any way bind them. The hydraulic lines have enough extra line to them (maybe a little too much since they curl up pretty high). The stiffness of the lines themselves would be what's fighting against the spin force as they press on the stabilizing arm. I hope these photos help you see the configuration I'm talking about. I very much appreciate your help on this. I want to be able to use this implement with confidence.


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## LouNY (Dec 15, 2016)

Looking at your pictures it looks to me like your hoses are what is preventing the pump from rotating with the pto, not the chains the chains should be what prevents the pump body from rotating. Also when you start digging is when the pump is going to build pressure and that pressure is what is going to try and rotate the pump and the stay chains need to prevent that.
Every load and unload cycle of the back hoe is requireing pressure from the pump, when no valves are being activated there is minimal pressure in the system, when you operate a valve is when the system will start to build pressure, the pressure the harder the pump force will try and twist the pump. By the appearance of the broken shaft that was likely caused by constant flexing of the shaft.
If it were my pump I'd run the chains under the drawbar each one separately and fastened to itself to stay fastened with minimal slack. Then repeat with the other chain.
They should not be tight to pull on the pump, but once the pump is turned on they should stop the housing from moving. If the hoses are binding they may need to be relocated and run diferently.


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## SHEF (4 mo ago)

LouNY said:


> If it were my pump I'd run the chains under the drawbar each one separately and fastened to itself to stay fastened with minimal slack. Then repeat with the other chain.
> They should not be tight to pull on the pump, but once the pump is turned on they should stop the housing from moving. If the hoses are binding they may need to be relocated and run diferently.


I completely understand your description and it really helped me to understand how better to mount it. Here's the new configuration I set up this morning. In the photo with my hand is me testing what would catch the pump as it attempts to move clockwise. The chain as it is mounted now stops it after about 5 degrees or less of rotation (not very much at all). The hydraulic line now doesn't stop the rotation which I agree is horrible strain on the hose. I might try to get a spring from the hardware store to move the hose more out of the way as it is mounted.

Other considerations I thought of while I was out there. In the third photo you can see a small metal lip at the bottom of the pump. This could be a spot for welding a torque bar setup. I'm not sure if it was designed for that (because it's a Chinese unit) but I can't ascertain that lip's purpose just by looking at it.

I also thought about translating the entire pump 90 degrees clockwise to move the hoses underneath the draw bar and out of the way (although these hoses are so long then they'd have to be restrained from hitting the back tractor tire. I think the chains would operate no differently so a spring restraining the hose that contacts the drawbar when the pump flexes is probably best.


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## LouNY (Dec 15, 2016)

Looks better if it stays up on the link.
I'd try and have someone watch and possibly video the pump and hose movement and hoe movement while digging for a bit.


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## SHEF (4 mo ago)

LouNY said:


> Looks better if it stays up on the link.
> I'd try and have someone watch and possibly video the pump and hose movement and hoe movement while digging for a bit.


We did tests all afternoon and there's no way to get the hydraulic hose to not act as the torque bar because of how the hose configuration that came preinstalled and attached to the backhoe. The hose hits the drawbar every single time. Until we figure out a fix the chain is irrelevant.


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## Busted Tractor (May 22, 2018)

Looking at the picture of the PTO shaft I can't see the broken end, but it appears to be a dark ring around the outer edge of the shaft. This would indicate it may has had a defect in it, and as you were using it it failed from a crack that was in the shaft.


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## LouNY (Dec 15, 2016)

Interesting the picture 4th over from your broken stub looks to be a different tractor was that from the literature that came with your hoe. It seems quite a bit different then your setup.
The hoe appears higher, the top link is sloped down to the tractor, the pump looks to be mounted upside down compared to yours, the pump below the pto shaft and the hoses are going straight back then up.


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## LouNY (Dec 15, 2016)

Also we have a difference in terminology were the hose is contacting to me would be your top link assemble.
The drawbar to me is under your pump were you would connect a trailer or wagon.
And your lift arms are the lower links your hoe is attached to.
You seem to be using your pto shield as a rotational stop for your chains
I'd recommend connecting your chains to the lower draw bar as it is stationary and will not move as the top link assembly and lift arms can and will.


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## SHEF (4 mo ago)

Busted Tractor said:


> Looking at the picture of the PTO shaft I can't see the broken end, but it appears to be a dark ring around the outer edge of the shaft. This would indicate it may has had a defect in it, and as you were using it it failed from a crack that was in the shaft.


When we had it repaired it was a warranty repair since the tractor itself is only 1.5 years old. The guy who did the repair said he'd never done a repair like this before ever. When I asked the question "Why do you believe this broke?" he responded by saying "It could be a bad batch. It's possible the metal didn't cure properly. There seems to be air pockets in the center of the shaft"
So he noticed the exact same thing you did and came to the same conclusion. 
So I'm definitely willing to believe that all things being equal this wouldn't happen again under the exact same stresses of the hydraulic pump. But I'm trying to make sure this pump is mounted in the best possible way.


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## SHEF (4 mo ago)

LouNY said:


> Also we have a difference in terminology were the hose is contacting to me would be your top link assemble.
> The drawbar to me is under your pump were you would connect a trailer or wagon.
> And your lift arms are the lower links your hoe is attached to.
> You seem to be using your pto shield as a rotational stop for your chains
> I'd recommend connecting your chains to the lower draw bar as it is stationary and will not move as the top link assembly and lift arms can and will.


Yes, you're absolutely right, and that placement did occur to me today and sounds like a much better idea. You're also correct about the image from the manual. It's a completely different pump and different setup that seems much better. I've been trying to contact with the salesman (he's responded to me queries before and been helpful) for the last 5 days (sending a message almost every day trying to poke him into weighing in on this) but he still hasn't gotten back to me. 

Do you think it would be prudent to get a spring that could loop around the hose and pull it away from the top link or should I be looking into rearranging the hydraulics all together to prevent the hose from contacting the top link during use?


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## LouNY (Dec 15, 2016)

You had me wondering what was going on and I looked for a manual on a BH7, seems like many of them call them BH 7's.
I'm wondering about the assemble of your hoe mounting. What I saw was that most had the A frame higher in respect to the tractors top link pin mount.
I see that your A frame is in the lowest mounting holes and has quite a slope to the top link bar. There is a possibility that when using the hoe if the bucket is pushing down hard the mounting arm on the top link could flex downward and could have actually hit the pump. I would consider raising the A frame so the top link is level or actually above the pin holes.
Also maybe reroute the lines through the A frame and back to the tank and valve body. Those fittings on the pump can be rotated after loosening the lock nuts to face the rear.
I wouldn't bother with a spring as those elbow fittings will not take the torque loading of the hose to the pump body for a long time.
Good luck with her


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## Qcumber guy (Jun 25, 2017)

LouNY said:


> You had me wondering what was going on and I looked for a manual on a BH7, seems like many of them call them BH 7's.
> I'm wondering about the assemble of your hoe mounting. What I saw was that most had the A frame higher in respect to the tractors top link pin mount.
> I see that your A frame is in the lowest mounting holes and has quite a slope to the top link bar. There is a possibility that when using the hoe if the bucket is pushing down hard the mounting arm on the top link could flex downward and could have actually hit the pump. I would consider raising the A frame so the top link is level or actually above the pin holes.
> Also maybe reroute the lines through the A frame and back to the tank and valve body. Those fittings on the pump can be rotated after loosening the lock nuts to face the rear.
> ...


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## Qcumber guy (Jun 25, 2017)

Greetings
The way you put the chain around the shield plate will bite you in the wrong place!!!!!
Just put the chains with equal lenths or 
slack sideways to the lift arms (with enough slack to alow for normal movement!!)


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## ck3510hb (Sep 12, 2016)

I have wondered about the Sheild and also you mentioned the hose was longer than needed, could you take the 90 degrees out and put in a 45 ? would that change the hose enough to miss the bar? Good luck


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## LouNY (Dec 15, 2016)

Qcumber guy said:


> Greetings
> The way you put the chain around the shield plate will bite you in the wrong place!!!!!
> Just put the chains with equal lenths or
> slack sideways to the lift arms (with enough slack to alow for normal movement!!)


Unless you have stay bars installed so the lift arms can NOT raise or move around I would not fasten the chains to the lift arms.
Too easy for them to be lifted or lowered while using the hoe.


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## AndrewInOz (Aug 28, 2021)

The chains should be so that they are at 90 degrees to the line between the PTO shaft center and the chain attachment point on the pump bracket (" torque arm length"). Like a breaker bar length.
Hard to see in the photo, but that distance looks very short. Like using an ultra short breaker bar.

IIRC theory from too many years ago :
This means that the chain tension is proportionally higher applying a shear force in the pto shaft of double the chain tension.
And the point this higher shear force is applied is way out in the pump bracket plane so there is a heap of bending applied to the shaft too as "overhung load".
So the shaft has the torque load ( that it was designed for ) plus unexpected shear force plus unexpected bending moment.

Think about one chain anchored and a winch on the other chain : can you winch enough load to break that shaft with those chains ? Its a lever with the pto shaft in the middle seeing 2x the winch. 
Bit of an ask given the shaft is seeing a simultaneous torque load too ....

Suggest
- Check the relief pressure is correctly set on that pump. Gauge its control valve pressure port and gently ( engine at idle initially) apply load. Under all conditions pressure should max out at manuf spec. I'd guess somewhere between 2000 - 2500 psi so abort testing if it goes higher. If this relief valve isn't working, something has to break.

- move where the chains attach to the pump further out from the center of the pto shaft. A steel bracket on the pump assy can be below that pto guard and extend out to the linkage arm area. Small amount to spend to clean up a possibly marginal combination.

- try keep that attachment point close as possible to the pto shaft support ( the bearing in the tractor )

- chain attachment point to the tractor so chains somewhere around 90 deg to "torque arm"

Unless elastic, only one chain will take the forward load. Hoses will be twanging straight before applying shaft breaking loads.

HTH's


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## John Liebermann (Sep 17, 2018)

Adding to AndrewinOZ, where is the torque arm to which the instructions refer? It is important that the lateral force preventing rotation of the pump be at considerable distance and at 90deg from the power center line.

The chain in the pics is absolutely an incorrect rotation preventor. .


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## SHEF (4 mo ago)

John Liebermann said:


> Adding to AndrewinOZ, where is the torque arm to which the instructions refer? It is important that the lateral force preventing rotation of the pump be at considerable distance and at 90deg from the power center line.
> 
> The chain in the pics is absolutely an incorrect rotation preventor. .


This is the photo given in the manual as the ONLY indicator of how to attach the pump. The pump sold with the backhoe does not match the pump in the backhoe manual photo so we're just making up the best situation from the advice we've gotten here. So many of you guys have been really helpful, which is great. I'm going to attach the bottom chain (left chain if you're facing the pump) to the drawbar straight down from the pump. The other chain will go up, and there isn't any structure on the tractor that's sensible to chain it to so I'm still working on that. 

I'm also waiting to hear back from the seller who has contacted his "engineer" and said he'll get back to us with a "working plan" -- Another option is to weld a torque bar to the lip that's at the bottom that currently isn't doing anything (see photo), and then forgo the chains altogether.


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## SHEF (4 mo ago)

This was the seller's response to my questions. He sent these two images saying that I should replicate these configurations:


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## pogobill (Jan 31, 2012)

It does look better SHEF


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## LouNY (Dec 15, 2016)

I like the hose routing, not a fan of the chain positioning.


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## John Liebermann (Sep 17, 2018)

The way those chains are hooked is a broken shaft waiting to happen. Look at the side force on the shaft, and as the shaft rotates it will eventually fatigue. 
Maybe if the pump does not pull hard you can get by. 

For me if it were mine as has been said before *"get the side loading off that shaft!"*

OK I'm history.


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## AndrewInOz (Aug 28, 2021)

Second that John.
Firstly to ballpark the load, lets assume a 100 LPM pump & with a relief pressure set at 150 Bar. 
At 540 RPM the pto needs apply 450 Nm of torque to the upspeed gearbox and on to the chain.
( only the one shorter chain takes the load )

Wild guess from the photo, the distance from the pto center to the chain attachment say 0.15 m or 6"
So a single chain tension will be 450 / 0.15 = 3000 N ( 300 kg or 675 lb ) *at best* when the chain is at 90 deg to the 0.15m line.

But in the photo , those long chains positions can never guarantee 90 deg. As 3PL arms lift, the lift links ( which are never vertical ) will be changing the chain anchor point + the links will bow in a bit or swing against the 3pl stabiliser chains.
It doesn't take much extension to this long chain length to make the comparatively short 0.15m move off 90 deg.

Load on the pto shaft goes thru the roof as you move away from 90 deg, As you have observed,,,

Like yr idea of deleting the chains. How about a solid bar protruding down captive by the drawbar frame. Welded to the existing bracket with the chains. Rather than welding/fixing to the speed up gearbox case.

The chain idea makes it easy for a manufacturer to ship out a " fits all ". I wouldn't worry about modifying to something more elegant. Not much work for a clean solution.
HTH's


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## SHEF (4 mo ago)

Again I want to thank you guys for all your help and advice. It took me a while to get back to this project because our honeybees swarmed this week which is a death sentence for bees if you don't catch them (anyways, I won't bore you with bee stuff). This is the configuration I setup with one chain down to the drawbar and one chain up to a spring that I setup. I also zip tied the hose back from the top link because until I fabricate a dolly to set the backhoe down on for storage (the seller "forgot" to send me the storage legs... then sent legs that don't fit the implement) I can't adjust the top link or move the hoses down underneath it. I powered up the pump and it definitely stays in place. When the backhoe's hydraulics are engaged you can see the spring tighten and flex. It "seems" to be a huge improvement over previous setups but I still haven't used that backhoe at high RPMs yet. 
What are your thoughts on this configuration?


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## Qcumber guy (Jun 25, 2017)

A Spring??????
Seriously???
So only one one chain will work now, the one to the drawbar


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## LouNY (Dec 15, 2016)

Looks better to me, one chain is sufficient all it does is prevent pump rotation.
Good luck using your hoe.
I'm still concerned why the first shaft broke.
Are there any burrs or marks on the pump housing like something may have smacked it.
I've seen those little 3 point hose move considerably while being used, I would be worried that the top link might have flexed downward
if the hoe was exerting force down. Such as would be done if trying to lift the rear of the tractor with the hoe to adjust the out riggers
or to scoot it sideways.


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## SHEF (4 mo ago)

LouNY said:


> Looks better to me, one chain is sufficient all it does is prevent pump rotation.
> Good luck using your hoe.
> I'm still concerned why the first shaft broke.
> Are there any burrs or marks on the pump housing like something may have smacked it.
> ...


My neighbor had the exact same thought, but he said he believed the pump housing was aluminum which would have dented immediately if anything hit it with any kind of force like the link smashing into it. There aren't any dents or marks. I also am very weary about the still unsolved mystery of why the shaft broke, and if it was a direct result of operating the backhoe or if it was already ready to break and the backhoe just was the implement on it when it did. As soon as I can fabricate a dolly for the backhoe I'm going to set it down and reconfigure the top link and the hoses to better positions.


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## John Liebermann (Sep 17, 2018)

The shaft was clearly a "fatigue" break.


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