Backhoe /TPH hydraulic conundrum (long)

   #1  

pycoed

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Zetor 7045; Wheelhorses C121, C101, A8;Cushman Turf truckster
I have a Long 445DT which comes fitted with a factory remote hydraulic valve intended to operate a double acting cylinder via two quick connects at the rear. Down feeds one connect & up feeds the other. It has previously been modified so that the lever-down valve outlet is piped to a spool block operating the front loader & a return pipe from that spool block delivers oil back to the transmission/tank. The lever-up outlet remains connected to a single rear quick connect.
So, to operate the FEL controls I have to hold down the factory valve lever with my right calf so that the FEL controls work, This is a bit inconvenient , but I could live with that. Now it starts to get a little more complex!...

I have just added a backhoe, originally a subframe type for some unknown tractor. The subframe was not suitable for my 445 'cos it fouled the 4 WD output & I wasn't keen on the hassle of fitting & removing the subframe.
I chopped & welded the subframe & welded on some mounts for a three point mounting, which seems fine & is easy to fit & remove. I have no rocky ground or heavy digging I need the backhoe for ditch clearing & general drainage work in a marshy area.

The backhoe uses the tractor hydraulics i.e. one pressure connection to the spool block & a return to tank. I used the existing quick connect for the pressure & added another for the return to transmission/tank. Now holding the remote lever up with a bungee, the backhoe controls all work well, except I have a problem: I am relying on the TPH arms to remain in a set position so that I can use the backhoe leg jacks to firm up the setup for digging. However when I down the boom, dipper or bucket to start a dig the TPH arms move up.
I have deduced that the TPH arms float if the remote valve is in use. Is this a correct deduction? Position control works fine when using a brush hog /mower/ rake etc so I think the TPH is OK. Can anyone suggest a way around this, short of using a PTO pump & separate tank for the backhoe hydraulics?
 
   #2  

RonMar

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Port Angeles WA
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Jinma 284 delivered 06/28/05
The ones I have looked at the guts on, have the 3PH litft arms not physically conneted to the piston. The piston can push on them to lift them, but if you lift on them with some outside force, they lift away from the piston linkage easilly. It is a single acting cylinder(configured to push arms up), so it couldn't really provide much down force anyway. I think they are designed this way to allow a 3PH impliment to float above the set position. The impliment weight and blade cut angle provide downforce...
 
   #3  

Farmerford

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John L.

I am not familiar with the Long, but on most tractors the three point hitch does not apply down pressure. It only applies up pressure to lift the implement or to keep it from falling below a certain height. (Old John Deere's and Farmall's (1940's) did apply down pressure, but that's another story). Therefore, when you apply down pressure with the bucket/stick/boom sufficient to overcome the weight of the backhoe, the backhoe will rise and bring the TPH arms up with it. I don't think changing the hydraulics will change that.

On the farm when we wanted a stationary drawbar on the TPH we used two steel bars the necessary length to run from the outer end of each TPH lower arm to the connection point on the tractor for the top link. Each bar was drilled at the end to allow the pins to pass through (drawbar pins at the bottom and top link pin at the top) and the ends were bent so as to be perpendicular to the pins. These bars kept the TPH from rising or falling. Note that a rising TPH puts the bars in compression, so they need to be fairly sturdy to hold the TPH down if there will be much up pressure.

Your experience points out one of the shortcomings of TPH mounted backhoes. I recall several years ago that the lockdown mechanisms for these backhoes (some sort of bar, perhaps as I described) were not strong enough and allowed the backhoe to rise up and crush the operator against the rear of the tractor or the ROPS.

Perhaps a member with a three point hitch mounted backhoe can enlighten us on how his TPH is kept down while working the backhoe.
 
   #4  

3RRL

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pycoed,
I have a question.
When you modified your hoe into a 3pt, did you make it so you have to remove your regular top link? Then there should be a rigid bar coming from the backhoe (bolted or welded to it so it doesn't move) that goes to the top link connection at the tractor. This takes the place of the regular top link.

The geometry of that set up is to keep the backhoe from rising up. The rigid bar and the lower drag links form a parallelogram of some sort to hold the backhoe up and but keep it from rising up further because it is rigid and does not collapse like a regular top link that has pivots on both ends.

Then there should also be 2 support bars that connect from the bottom of the backhoe (from each lift pin) up to that rigid top link bar for added rigidness.

Here's a picture of mine. Look at the rigid top link bar and the side bars that should be bolted to it.
Do you have both rigid side bars and the rigid top link?

 
  
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pycoed

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3RRL said:
pycoed,
I have a question.
When you modified your hoe into a 3pt, did you make it so you have to remove your regular top link? Then there should be a rigid bar coming from the backhoe (bolted or welded to it so it doesn't move) that goes to the top link connection at the tractor. This takes the place of the regular top link.

The geometry of that set up is to keep the backhoe from rising up. The rigid bar and the lower drag links form a parallelogram of some sort to hold the backhoe up and but keep it from rising up further because it is rigid and does not collapse like a regular top link that has pivots on both ends.

Then there should also be 2 support bars that connect from the bottom of the backhoe (from each lift pin) up to that rigid top link bar for added rigidness.

Here's a picture of mine. Look at the rigid top link bar and the side bars that should be bolted to it.
Do you have both rigid side bars and the rigid top link?



Ah! I think we might be on to something here! Many thanks for the responses.
I am using an ordinary toplink. I realised the TPH arms would not provide downforce, but I thought they would passively resist any upforce as they seem to do when using a brush hog. Perhaps I am wrong about that too!
I didn't realise that the backhoe would need to be ridgidly mounted - this would mean that the TPH can not be used to raise & lower the hoe for transport at all? So I would need to decide on a suitable height for the backhoe to be set at to provide adequate transport clearance when the llegs were raised, & then fix the linkage at that height once & for all, with a ridgid toplink & braces. Then I just need to operate the jacking legs to firm up for digging?

I do have diagonal braces (which are not actually in place whilst I am experimenting ) which run from under the seat mount back to the remains of the subframe. These would not provide the trangulation to the TPH parallellogram you show in your excellent photos , but I could arrange your sort of setup fairly easily.
I had dispensed with the seat & intend to operate from the tractor cab kneeling on the tractor seat & using the controls from the cab via the back window opening. I thought this would be safer than sitting on a backhoe which could be raised by the TPH. Perhaps this may now need to change as well...
 
   #6  

3RRL

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I didn't realise that the backhoe would need to be ridgidly mounted - this would mean that the TPH can not be used to raise & lower the hoe for transport at all? So I would need to decide on a suitable height for the backhoe to be set at to provide adequate transport clearance when the llegs were raised, & then fix the linkage at that height once & for all, with a ridgid toplink & braces. Then I just need to operate the jacking legs to firm up for digging?
Exactly.
The regular top link has swivels on both ends and is designed to allow pivoting up and down and even sideways a little. You want to eliminate that for the backhoe mount with the rigid top link and side braces. When you put the outriggers (legs) down, you may find it even picks up the rear of the tractor a little. Then you know you have accomplished it perfectly.

That locks up the three point movement and yes, you need to determine it's position on the tractor for
a) working height
b) transport

That's a controversial area because the lower you mount the hoe, the deeper you can dig and the farther you can reach.
But then it affects how well you can transport it over swales or gullies or bumps.
Pick a height that is a happy medium. IMHO, you want to mount the hoe as close to the rear of the tractor as possible and with enough height off the ground for travel so you don't get stuck somewhere. I feel the digging depth can suffer a little.
Glad we got to the bottom of the problem.
 
  
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pycoed

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Farmerford said:
John L.

On the farm when we wanted a stationary drawbar on the TPH we used two steel bars the necessary length to run from the outer end of each TPH lower arm to the connection point on the tractor for the top link. Each bar was drilled at the end to allow the pins to pass through (drawbar pins at the bottom and top link pin at the top) and the ends were bent so as to be perpendicular to the pins. These bars kept the TPH from rising or falling. Note that a rising TPH puts the bars in compression, so they need to be fairly sturdy to hold the TPH down if there will be much up pressure.

Right - together with Ron you have made this a lot clearer for me thanks. I take your point about potentially getting crushed under the ROPS in the cab too, I'd decided to try to operate the backhoe from within the cab for just that reason!
I'll have to do a bit of trial & error to get the bars right, since the transport height might be tricky for me - that's one reason I decided to try the TPH mount since I thought I'd ne able to lift the hoe clear of obstructions with the TPH. Now I know I'll have to make some compromises... my land is all soft & marshy & I need the hoe for ditch clearing & general drainage. I can see a fixed backhoe height might lead to some problems once the back wheels dig in a bit.
Bit of a bummer - two kids in college spending money like water leaves poor old dad with no means to buy a 360 digger (even if I could hide it from "the boss"!!)
 
   #8  

B8200er

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Hello, this is my first post on this forum. I thought this might be of some interest relative to this thread.

I am mounting a used small TPH backhoe on my Kubota B8200. Currently it has fixed legs (although the length of the legs is adjustable with pins), and relies on the TPH to lift the backhoe for transport.

This backhoe came with a hydraulic cylinder with one end pinned at the rigid top link (very heavy duty) near the tractor's top link attachment point, with the other end of the cylinder pinned at the bottom center of the backhoe frame between the pins for the TPH lower attachment arms.

Now for the strangest part ... the cylinder is setup for one-way operation to only extend the cylinder rod under force ... AND, there is no control valve for the hydraulic line going to this cylinder! There is just a "T" connection into the pressure (incoming) hydraulic line from the tractor's pump.

After thinking about this for awhile, it dawned on me how this is supposed to work.

Assume every thing is hooked up, the backhoe is resting on the ground on its fixed legs, the tractor is pumping oil through the open center spools on the backhoe. There is very little or no pressure in the hydraulic line going to the backhoe, so this one-way cylinder is not exerting any force or trying extend itself. At this time, the tractor operator could use the TPH to lift the backhoe, which would simply compress the extended cylinder rod. Or, if the operator were to operate the backhoe and exert downforce with the boom/bucket (i.e. dig), this would cause pressure to rise in the hydraulic line, extending the cylinder rod, pushing UP on the rigid toplink near the tractor's toplink pin, thereby trying to lift the back of the tractor while pushing DOWN on the backhoe support legs.

As far as safety goes, if a hydraulic pressure line bursts, you get a simultaneous loss of downforce for digging and of the pushing force of the one-way cylinder.

Has anybody seen anything like this setup? :confused:

B8200er
 
  
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pycoed

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B8200er said:
After thinking about this for awhile, it dawned on me how this is supposed to work.

Assume every thing is hooked up, the backhoe is resting on the ground on its fixed legs, the tractor is pumping oil through the open center spools on the backhoe. There is very little or no pressure in the hydraulic line going to the backhoe, so this one-way cylinder is not exerting any force or trying extend itself. At this time, the tractor operator could use the TPH to lift the backhoe, which would simply compress the extended cylinder rod. Or, if the operator were to operate the backhoe and exert downforce with the boom/bucket (i.e. dig), this would cause pressure to rise in the hydraulic line, extending the cylinder rod, pushing UP on the rigid toplink near the tractor's toplink pin, thereby trying to lift the back of the tractor while pushing DOWN on the backhoe support legs.

B8200er

That sounds a very elegant solution! I've done something similar with mine, only mechanically rather than hydraulically, but I like the sound of a single acting cylinder tee'ed in...
What I've done is to add the triangulating brace & fabricated a new hefty toplink from 3"X3/8" bars spaced about an inch apart. The triangle brace goes from each TPH bottom pin up to this new toplink near the tractor where I've welded in some 1" round bar as a cross pin on the toplink. The brace has a matching ratchet style hook 3/4" wide that catches on this when it is raised by the TPH, thereby locking everything up. When you drop the TPH, you can disengage the ratchet tooth from the cross pin & the TPH can then be used to raise the backhoe.
I'd take some pictures, except the tractor & backhoe are now marooned in a sea of water after 48 hours of torrential rain! - Still I got 6 nice mallard tonight at evening flight, so who wants to mess about with tractors in the rain!
Thanks for the post, I'll see how mine works when I get to grips with some serious digging (if this rain ever stops), but I really like the "hands free" sound of your idea
 
 
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