I am working on a JD 120c. this unit has a Hitachi pump system. This piece of equipment has been working just fine until the other day when it quit any and all hydraulic functions. I found that the piggyback or charge pump had sheared the pump input shaft. I replaced the pilot filter housing, that seems to have a sort of relief valve in it? I replaced all the hydraulic filters and checked the return to tank line from this pilot filter housing, it was clear. I replaced the pump, purged it ,fired the unit up and snap goes the small, charge pump shaft. The local JD dealer doesn't have a clue, they came out, checked it, put a pump in it, and the same results, broken shaft. Does that pilot filter housing really have a relief in it or should I be looking further up the system? Any ideas? or does anyone know how this system works? Getting expensive. Thanks for any help. Bill
Yes the pilot fiter head as a relief in it.May be setto high .Check out page 444 inthe manual downloa this http://www.4shared.com/document/pGf2_kQL/JOHN_DEERE_120C_2002-__2899.html check out part 51
I'm not a Deere tech, but I'd wager that valve in the pilot system filter isn't actually a relief valve as much as it is a by-pass valve for when filter gets clogged. When your first pilot system pump went down, did you check the filter for metal fragments? If it had a lot of metal in it, chances are it popped open the by-pass valve and sent junk into the pilot system control manifold. The pilot system on most excavators is a pressure regulated system, the pressure on the pilot controls is only a few hundred pounds, and that gear pump is capable of putting out thousands of pounds of pressure. The pilot system manifold has various components to regulate the pressure and flow of oil from the pilot pump. It's a good possibility the manifold components and spools are fragged with debris from failed pump.
Willy that is what Deere is call it in their manual.But would thing it is more of bypass also.I have workshop and tech manuals will have to look at them closer.They show adjusting the pressure on the top of filter head with shims.Then checking the relief pressure.Her are the proformace test tech manuals for JD120 that I have. http://www.4shared.com/document/uwKRRnNq/PROFORMANCE_TEST_CONTENTS_155T.html http://www.4shared.com/document/0tX71qld/PROFORMANCE_TEST_CONTENTS_155T.html These are two different books.Check them out.Hopefully they help.
After installing new pilot pump did you measure the pilot pump pressure? Can you post pictures of the broken pump shaft?
Yep, that's what they call it TK, seems the guys who write and produce parts books/pages forget that words mean things. LoL
Thanks Tool King. That link to the service manual is a life saver. Come Monday morning I'll get back to the job site, out in the woods where it chose to break down, (could have been in a worst place though) I'am going to check that new filter housing and see just how many shims they put in the relief valve, the old one had only one. Thanks again, I'll keep you posted, revbill. "I don't care that others charge less for their work, they know what their work is worth"
willie thanks for the help, I'll be inspecting all items up line to be sure that there is no junk in them. I'll keep you posted, revbill "I don't care that others charge less for their work, they know what their work is worth."
Thanks again Tool King for the new links I'll keep you posted. revbill
rgl726 Thanks for your post, yes tried to check the pressure but pump only lasted 5 to 10 seconds, I didn't get a good read. I don't know if JD tech tried to check pressure or not, I was not invited to that party. I'll keep you posted. revbill
revbill let me know if you need the any other part of the workshop or tech manuals for this machine.I have it for general ,engine,undercarriage,front attachement ,toubleshooting and wiring diagrams .Let me know.
Tool King I'll let you know about the other manuals, thanks. Looking at what I've already down loaded from you, it sure looks like the relief valve on the pilot filter housing is not opening, or like you said the pressure is too high. Well, I'll find out in the next couple of days. Thanks again revbill.
revbill, I wish I knew more about your machines system than I do, but I really think you're looking at this completely wrong and are therefore unable to see you're problem. You have to keep from thinking of that valve as a relief, which is an acceptable generic term, but most filters incorporate a by-pass valve, which more properly describes its function. All that means is if/when the filter gets clogged and restrictive, the by-pass valve opens and allows the flow of oil to carry on by "going around the filter", effectively sending unfiltered oil to system components, which I have a suspicion is the case with your machine. Hence the reason I asked previously if you checked the filter element for debris when the first charge pump went down. If I'm right, when that pump grenaded inside and sent fragments to the filter, the filter clogged, by-pass valve opened, fragments went to pilot manifold valve body, and now the valve body has all these fragments messing up the operation of the internal pressure regulating spool. If that's the case, you'll have to completely disassemble the pilot manifold valve and get the junk out of it.
One way that I use to check for any problems downstream before installing a new pump. 1. If you don't have one, purchase a hand pump like an Enerpack. A cheap HF one will work but make sure to flush out whichever you have. 2. Check with the dealer for the normal pressure in the system that you are checking. 3. Install a good known pressure gauge in the line and connect your hand pump, bleed the line of air. 4. Pump up the pressure and see if the pressure is controlled within specs, watch your pump reservoir level. Obviously this will only work with a system that is closed center or a pilot pressure regulating system. Or suspected of being blocked ahead of any reliefs. I use a small variable displacement motor driven pump with a variable pressure control, it saves some expense and time.
Willie59 feel free to download them yourself . http://www.4shared.com/document/uwKRRnNq/PROFORMANCE_TEST_CONTENTS_155T.html Check out page 27 and after it shows how to adjust pump. Not saying this the told fix but at lease lining up his ducks in a row. I am interested in see what he finds with machine.I figured I woud give the manual to have at leased something to work with .
willie59 sorry I didn't mention about the pilot filter. There was a small amount of aluminium in the filter. Here is what I believe happened to the first 2 pumps, after tear down of the pumps I found that pressure had built to a point that the rotors were forced apart slightly, causing them to dig into the outer wall and lock the pump, snapping the shaft. The debris is aluminium, and a very small amount. You are right, the pilot filter housing contains a by-pass valve, as well as a relief valve in another location in the housing, taking no,so I thought ,chances of a malfunction within the pilot filter housing, I replaced the housing with a new one. Also the manual on this machine from tool king, shows this filter housing as having the only adjustable relief valve in the pilot system. Like I said in a previous post, I'am taking your well taken advice and I'll be checking everything up stream. Again thank you for your help, sometimes I need all I can get. I'll keep you posted. revbill
Make sure everything is clear up stream in the system.Glad to heard yu are making positive headway with machine.Hope the manual were help with this machine.
BillG Thanks for the tip, I believe I still have a Enerpack back at the shop, haven't used it for awhile. Thanks again. revbill
Ok, that's interesting. But keep in mind, in typical hydraulic circuits, relief valves are for just that, to relieve excessive pressure. But it's typically not desirable for a relief to be popped open, especially under continuous circumstances, because relief valves are restrictive in a circuit and will heat the oil excessively. The fact that the pump has wear against one side indicates it was working under excessive load. In that pilot circuit, this would be less the fault of the pressure relief valve and more likely the circuit pressure regulator not working properly.
willie59 Boy that's a point well taken. I went back out to my service truck and looked at the old filter housing and the (relief valve?) It's not like a standard relief valve, its in the shape of a small spool valve, It is spring loaded and adjustable by shims of various thickness. Perhaps this really is a pressure regulator and not a relief valve as you suggested. I'am not really this hardheaded. Just the forest for the trees kinda thing Thanks again I'am out for the nite revbill
Well, it sounds like you're beginning to cut down some of the trees. Most excavator pilot systems are a low pressure system, only a couple of hundred pounds of pressure. The oil for the pilot system is typically delivered by a gear pump, and somewhere in the pump output circuit will be some form of pressure regulator that maintains a low pressure on the pilot circuit. Any oil delivery that is over and above what is needed in the pilot circuit is dumped back to tank by the pressure regulator. I'm thinking that's where your problem is, whatever regulates the pressure on the pilot system.
Hay Ya'll Typical Monday, spent all day chasing equipment from Ft.Benning Ga.to Alburn Al. Was unable to get back to the JD120 with pilot pump problem. Maybe tomorrow. Tool King Do you have a line drawing hydraulic schematic, it sure would be helpful. Thanks revbill I will keep ya a'll posted
revbill look at page 28 hope this helps you out and also look at the rest of this manual. http://www.shared.com/document/EyVQYLus/COMPONNT_OPERATION__CONTENTS_1.html
Tool King Thanks a bunch, I think that info will do the job. I'll keep you posted revbill
Tool King Couldn't get that link to do anything -- maybe its me?
try this one http://www.4shared.com/document/EyVQYLus/COMPONNT_OPERATION__CONTENTS_1.html The 4 was missing for some reason
revbill what company do you work for or are a private mechanic .Just wonder that is all . I work a road mechanic here in New Jersey so I know what you are going through with this machine.
Tool King Glad you asked, I work for a small equipment rental co. We have 2 locations, and are giving RSC, United and Sunbelt a run for the money, and are doing pretty good. Thanks for checking that link-- works fine now Got to get some sleep, morning comes early. revbill
tool_king, do you have an actual hydraulic shematic of the pilot circuit? revbill, The info last posted by tool_king does verify that it has a pilot gear pump which means somewhere there should be a relief valve. It could possibly be in the housing you have replaced, if that is the case you will have a (3rd) return line that goes back the the hyd tank or a return manifold. If the filter housing only has 2 lines, one in, one out, then there is not a system relief in it, only a bypass. It sounds like the pump is deadheaded somehwere down the line, and the pump may be only be designed for low pressure. Your description of the internals of the grenaded pump seems to confrim this. As long as the tank is clean, and your suction hose is clean, you should not have debris entering your pump. I would assume that your system uses hyd return filters, as any good hydraulic system should. Some systems even use a suction screen on each suction lines inside the tank. Since you have inspected the system, I would venture to guess, it is not debris causing the issue. If you are confident there is not debris entering your pump, you can run a hose from the outlet- pressure side of the pump direct to the tank, plug the hose you removed to prevent backpressure leakage and start the machine. All should be good. If you have access to a flow meter with a pressure gauge and restrictor installed, you can restrict the pressure to the JD pilot spec just for the sake of checking the pump. While not necessary, either of these procedures will verify your issue is on the pressure side of the circuit. Next, you need to determine, without doubt, where your system relief is. Have a pressure gauge "T"ed in the line out of the pump. Normally, system reliefs are either adjustable or non adjustable cartridges in a block, but I suppose it could very well be a piloted spool valve using a shimmed spring. Regardless, before starting the machine, make sure either the relief is backed all the way out, or all of the shims are removed, and if it is a piloted spool valve, make sure the spool moves FREELY and is not stuck. If you have a cartirdge style relief, pull the cartridge and check for debris in the end of it and make sure the spool moves (you could just replace it if there is any doubt), all it takes is a small piece of rubber from a hose or oring to block it. Also make sure the return line from the relief to tank or return manifold is clear. Remove the pilot pressure line (out) and install a hose directly back to the tank AFTER the relief valve, then start the machine. If everything is working properly, you can now set the relief to the JD specs, which should only be around 200-400 psi as others have mentioned here. At this point you can reattach the pilot pressure hose and should be fine as the relief will be doing its job. Just a couple notes, it is unlikely, but possible that the inner lining of a hose can seperate and block off flow, I have seen this happen with a hose that was pinched, but looked ok on the outside. If in doubt, replace the hose, and make sure you blow out all hoses before installing them. Rubber particles will wreak havoc in a hydraulic system. It is particularly critical to make sure the spool in the relief valve, whichever type you have will move freely. If you cant tell, then replace the valve. Always back off any adjustable type relief before starting the machine, then slowly adjust it up to spec with a reliable gauge in the system. I tried to find hyd shematic online but was unable. If tk can provide that, we can better determine exactly what type relief it has. Also a parts illustration will show what it looks like.
MTI Mark This the part manual I posted in my first post on this. Check out page 444 inthe manual downloa this http://www.4shared.com/document/pGf2...02-__2899.html check out part 51
rebill How did you ever make out with you machine ? With the pilot pump problem . thanks ED
be sure to pull ur oil cooler and have it cleaned iwould hate to hear that the system is not getting cleaned correctly........just sayin..