Go BottomThree Point Hitch Problem
 | Larry K
Join Date: Posts: 1 
|
2001-07-16 30111
Having a problem with my 3ph on a John Deere 1050. When moving round bales around 1100lbs, the 3ph will raise the bales fine and hold for about 5 sec. and then suddenly drop. If I get the tractors rpm up enough when starting to move it will usually hold and not drop, any suggestions why the sudden drop at lower rpm. No chatter or whining noise when lifting. One note, never had this problem until I installed a power steering kit to the tractor. Any suggestions, input, or thoughts would be appreciated.
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
|
2001-07-16 30114
I guess the PS is run from a priority valve. I can hear when my PS is active and demanding oil from the priority valve. If I can't hear it, I have to assume the PS is not demanding oil and shouldn't affect other hydraulic operations. You might note if the 3ph drop happens only during a turn. I haven't thought about it, but I guess it's possible for the PS to demand more oil than the pump delivers at low RPM. If the 3ph was in lift mode, I guess a 3ph with a heavy load could back-feed the PS trough the priority valve. If PS demands more oil than the pump delivers at low RPM, the line pressure could decrease to less than the 3ph cylinder pressure. However, even if it's possible, the tractor would have to be in a turn and the 3ph in lift mode. I'd check the 3ph adjustments to make sure the it actually goes into and stays in a neutral mode. If it drops while in neutral, the PS is even less likely an explanation. If it still drops, you might turn off the flow control valve. Then, if it still drops, valves in the 3ph may be faulty (the unload and poppet valves are the ones I hear mentioned). These valves exhaust into the normal 3ph oil return path. Turning off the flow-control valve closes that path and would be a pretty good diagnostic. If it still drops, the 3ph safety relief valve may be faulty. I'm not 100% certain, but I believe the safety relief provides a return path independent of the flow-control valve. If it drops with the 3ph in neutral and while driving, you might note if it happens when bumps are hit. Bumps create load shocks that increase the cylinder pressure. Bumps and heavy loads could pop a weak safety relief. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| John Mc
Join Date: Feb 2002 Posts: 98 Vermont
|
2001-07-16 30115
TomG: Wouldn't he actually have to be in the act of turning the wheel for the power steering to draw on the pump? I would think that the tractor being in a steady turn, the PS would not be drawing anything. I thought it only drew while actually moving the wheels, and stopped drawing (or drew almost nothing) once the front wheels were in their new position. But, perhaps my understanding of how PS works is all wet.
....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
|
2001-07-16 30125
Good question John. I guess I didn't actually distinguish between a turn and active PS. I meant when the PS is active, which I can hear on my system. As I say, I don't know if the idea of back-feed is even possible. It is an interesting idea though. Regarding your question whether oil flows through the PS system in a constant turn: I'm not sure of the answer. There is a spooling valve that opens a line from the priority valve to the PS sector/cylinder when the steering wheel is turned. There also is a return line to the sump and a pressure relief valve in the sector/cylinder. The return line and pressure relief valve provide the possibility of oil flowing through the PS system to the sump when the PS spooling valve is open. As near as I can tell from a quick reading of my repair manual, the spooling valve is moved by end-thrust from the sector gear. End thrust is created only when the steering wheel is being turned and not when it is simply off-centre. In absence of end-thrust, the valve centers and the spooling valve closes. If that's correct, you're right, and I also ended up learning something concrete rather than theoretical. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| Larry K
Join Date: Posts: 1
|
2001-07-16 30127
Thanks for your replies. To clarify the situation, once I lift the bale the wheels are straight and no power steering is in use. I then have to quickly rev the engine and get it rolling before it drops. I noticed at times it may drop two to three inches and at other times it may drop all the way to the ground. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
 | Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
 Pics
|
2001-07-16 30130
I hate to be the spoiler in all this but here I go anyways. The 3pth, as with any hyd. cylinder, requires a valve in the circuit to direct fluid to & from it, to create the controlled motion we desire. If your 3pth is dropping without any input from you, this means that either the seals in the valve or cylinder are allowing the hydraulic fluid to escape instead of being trapped in the cylinder and holding up the load. Get it checked out.... Best of luck. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| Larry K
Join Date: Posts: 1
|
2001-07-16 30150
I raised the 3ph system with a lighter box blade while the engine was off, it bled down rather quickly. This leads me to believe it probably has nothing to do with the new power steering. As Tom and Murf said most likely a worn "o" ring on the piston, worn spool valve, or worn check valve. Does anyone have experience rebuilding the control valve or replacing "o" rings/piston rings on the hydraulic piston? Seems pretty simple to rebuild, are parts available? Any special tools required? Any forseen problems I need to know about before I break the system down? Any thoughts or suggestions would be appreciated, thanks again for all replies. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
|
2001-07-17 30156
I haven't done it, but rebuilding the 3ph does't have a reputation for being a real difficult job. A manual should be available and studied, and a manual should list any special tools needed. I was making some theory to think through if it's possible that PS could be involved. I still not sure but seems to hinge on how a priority valve works. I still haven't entirely come to grips with priority valves. However, it seems certain that flow to the high-pressure line would have to be restricted as the flow to the PS increases, or little pressure to the PS would be developed. A spring-loaded plunger in the priority valve seems to prorate the flow. What I haven’t figured out is if a very high pressure in the hydraulic line could overcome a very low pressure in the priority valve. If it can, then it seems possible that a heavy load on the 3ph could cause a back-flow from the 3ph cylinder through the PS system when the 3ph is in lift and the PS is active. I don't think it's being a spoiler to tell that some of my theorizing is a bit obscure and off the mark. That's often the case. Though I do hope my ramblings were maybe a little helpful in suggesting some tests that could narrow down the problem a bit. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| Roger L.
Join Date: Jun 1999 Posts: 0
|
2001-07-17 30161
It never hurts to look at "zebra" theories....as Tom has done. And I know of no better way to understand a system than to think about the myriad ways that it can fail - again as Tom is doing with the power steering study.
But the first place to look is the most common reason. I agree with Murf. The 3pt is a closed system. Oil is forced into the 3pt cylinder and piston when your hand on the quadrant lever opens the 3pt valve, and the oil is trapped in there when the valve is closed. If there were no leaks in the 3pt system, the 3pt should then stay up indefinitely - regardless of engine RPM and even with the engine off. If it does not stay up with the engine off, then I would look at the O ring on the piston, the spool valve, and at the 3pt check valve. If the 3pt is responsive to engine RPM, then the first place to look would be that spool valve.
I've rebuilt the 3pt spool valve - I call it the quadrant valve sometimes - on other tractors but not on yours. It was easy and straightforward. Don't be surprised if you don't find any obvious problem. Just go ahead and replace all the o rings in there and my experience has been that this will fix the problem.
....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
|
2001-07-18 30201
I haven't heard the metaphor 'zebra theory' before. Interesting possibilities here. Maybe it's like zebra stripes--no two theories about a subject are the same. That could describe my theorizing pretty well. At any rate, I am kind of obsessive about how things work. Normally I have to take them apart to figure it out. However, at the rate my tractor breaks, I'd be in a rest home before I have a clue about the tractor. Guess I have to theorize. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| Roger L.
Join Date: Jun 1999 Posts: 0
|
2001-07-18 30214
Tom, I'm not surprised you never heard of the "zebra theory". Is's known locally as a "Rogerism". I heard the term once in Vet medicine - I don't know the context - but it appealed to me so I've sort of stretched it out to cover mechanical work as follows:
Imagine you and a few friends can see off in the distance the figure of a cowboy working his cattle. Its so far away that all you can see is his outline - if there were any stripes on his mount you couldn't make them out. But the profile is definitely equine. Now most people are going to make the assumption that he is riding a horse, but in every group there is one guy who will point out that you can't eliminate the possibility that he might be riding a zebra.
Mechanics is like that. You don't ignore the possibility of a zebra, but you proceed on the probablility that it is a horse. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
Pics
|
2001-07-18 30216
Actually, Roger, with where you are located geographically I would be inclined to think someone would mention a mule before a zebra........but then that's just me. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| droz
Join Date: Posts: 1
|
2001-07-19 30242
FYI, the "zebra theory" is used mostly in medicine. Such as, if you hear hoof beats, think of horses not zebras (in the US of course). Thus, look for the obvious diagnosis, not the obscure ones. Also known as Occam's razor for the really pedantic. Necessary information for tractor people. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| Kenny
Join Date: Mar 2004 Posts: 46 sale creek
|
2001-07-19 30245
Larry, There is a possibility that the steering has a role in your problem. It is not causing the problem ,But it may be worsening an existing problem in the rockshaft. The power steering prioroty valve siphons off 2 gallons per minute at all times, whether or not you are steering. So if you have a bad seal or valve in the rockshaft, there is not as much available flow as before. If you repair the rockshaft , your problem should be solved, although it may not be as fast to lift as before . Kenny ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
|
2001-07-20 30251
Thanks to Kenny's comment, I looked at an oil flow diagram and found that the neutral position opens both the left and right steering ports, which provides a path to the sump. Oil flows continuously, but activating the steering does seem to increase oil flow. I suppose it would be good to find out what kind of tractor and what kind of PS kit was added before entirely eliminating the PS. Some older farm tractors have pumps that are barely large enough to run a modern PS steering system alone. I also note that the problem was described as periodic drops ranging from a few inches to the ground that were reduced at higher engine RPM. I believe the 3ph leaks down when off and the 3ph in neutral. I don’t know if the leak down and drops are the same things, and I don’t know if the obvious explanation changes for a drop as opposed to a leak down. Guess I should note that I wasn’t using a zebra theory to suggest an alternative diagnostic explanation to be pursued, but more like a method of identifying unlikely ones. Reasoning through what would have to happen for PS to be the explanation seem to make PS an even less likely explanation. With respect to zebras and Occum: I’m not sure if enough information is present to focus on a single component, or even if that’s desirable. The 3ph leak down probably should be repaired. I’m guessing that complete rebuild kits are available and such a kit would have a good chance of fixing any and all problems described. I suppose there is a risk of ‘shot-gunning the repair’ and missing the actual problem. Another tear-down could be required. The nature of my work gives me an epidemiological rather than clinical approach. I know that Occum’s razor regularly cuts too fine in which case a cliché may reverse and 'believing is seeing.' Adequate information to produce an explanation must be gathered. However, zebra chasing in clinical settings shouldn’t be done. Every zebra requires more diagnostic tests, and every test has it’s own morbidity rate. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
Pics
|
2001-07-20 30252
Maybe I'm not being clear enough, maybe I'm wrong, but here goes again. Think of your 3pth as a simple plumbing system, like the water system in your house. If this is the analogy involved, and you fill the bathtub with water and then shut off your water pressure system (close main valve or unplug pump) does the bathtub empty? Of course not, it is now a completely isolated body of water. This is precisely the case with your 3pth circuit. Once the 3pth (or any other circuit, ie loader) is pressurized and the valve closed, it is isolated by the valve from the remainder of the circuit(s). The proof, raise your 3pth with a load on it and shut off your tractor, does the implement stay up? It should unless the hyd. fluid is escaping somewhere past a seal. I agree that most small units have some sort of priority flow control system, but this only affects the "live" portions of the circuits, ie the parts of the circuit with flow, such as the power steering, or hydro. drive, NOT static portions. It is sometimes a difficult thing to get your head around I realize, but a priority valve CANNOT cause this problem, only a fluid leak from a suspossedly closed system could. Best of luck. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| Roger L.
Join Date: Jun 1999 Posts: 0
|
2001-07-20 30253
Go Murph! I agree. The 3pt is an isolated system. It is isolated by the 3pt control lever. We've been through this in earlier responses. If the level of the 3pt lift arms changes once you take your hand off of that lever, then either the lift cylinder is leaking past its rings (or safety valve), or the control valve itself is leaking. In my experience it is usually leakage past an O ring or check valve. Taking the system apart, cleaning everything - don't forget the check valves - and replacing all O rings usually fixes it - even though you may not be able to find an exact cause. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
Pics
|
2001-07-20 30254
Thanks for the endorsement Roger, as you alluded, I too have found that in most cases a nick in an "o" ring or seal almost invisible to the naked eye is enough to cause real headaches. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| kay
Join Date: Posts: 1
|
2001-07-20 30258
Well said Murf. This thread has continued with the original underlying thought that "it started when the power steering was added" or something close to that. I keep thinking that when the power steering was added, some debris may have been introduced into the system that found its way to the seals and/or O rings in the 3pt system, resulting in the leaking problem as Murf simply describes so well. ....
Reply to |
Quote Reply |
Add PhotoThree Point Hitch Problem
| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
|
2001-07-21 30277
I think everybody is saying about the same thing. Rebuilding the 3ph mostly likely will fix everything. The rest of the discussion can be viewed a learning exercise. I'm not sure how well that's going at the moment. I know I create my own problems by long posts. However, incomplete learning often is accompanied by too many words. My original point was that PS might be eliminated from the problem by ensuring the 3ph is in neutral mode and then seeing if it leaks down. I think that's what's being said. I said it too and sometime ago. It was a piece of learning for me. The 3ph is an isolated system when it's in neutral, but not when it's in lift. It seems like a simple diagnostic to me. If there's any doubt, put a heavy load on the 3ph, put it in lift mode at low engine rpm, activate the PS by turning and see if the 3ph drops. Probably not, but it does seem like a simple test for an improbable condition. For learning purposes, I think I've got it figured that in lift mode, the priority valve sees the pressure developed in the lift. Conceivably at low rpm's the additional flow required by an activated PS would result in decreased pressure in the input side of priority valve. What happens to the higher pressure on the output side of the priority valve? Could it produce a 3ph drop; a leak-down? I don't know, but it seems like a decent enough question to be taken up here for the purposes of learning, and it probably has a fairly simple answer. I wish I could do these things in fewer words and perhaps be better understood. Or, maybe there's actually no interest in such things here. Anyway, I’ll go with the flow, but I think that probably everybody should move on past this one. ....
Reply to |
Quote Reply |
Add Photo
Go Top
Share This