Hello all. First of all just wanted to say this is a great forum with a great deal of information and very knowledgeable members! I spent alot of time reading and searching but haven't quite been able to quite find the info I am looking for for this particular issue. Hopefully we can get this solved and help others in the future. I am currently working on a friend's backhoe in exchange for free use of it - but I am beginning to regret this deal lol. The machine has been fighting me every step of the way. Anyways it is a Case 580 SK - phase 3 (shifter on side panel) w/ extendahoe. Among other issues, I have been resealing/packing hydraulic cylinders that are leaking. Latest one I did was the boom cylinder - was an absolute bear to do. Now it doesn't leak (externally) anymore, but sags quite badly; it lowers on its own about 1"/sec (pretty much unusable). It did NOT do this before I resealed the cylinder. So based on my knowledge and research on these forums I think I have narrowed it down to 3 culprits: 1. Oil bypassing piston seals inside the cylinder (really hope not, maybe I damaged them during reinstall? I have done 10+ cylinders just in the last ~month without issues...) 2. Piston relief valve (inside the cylinder, see #13A in the picture) has failed and is letting oil through? Can someone explain to me how it is supposed to work/how to test it (preferably without disassembling cylinder again). I did need to heat the rod/piston quite a bit to get the bolt out, maybe I damaged the relief in the process?? 3. Issue in the boom control valve, bad seals and/or crud in the valve, allowing oil to pass through? (strange coincidence?) I plan to run into the city today to pick up some JIC caps/plugs and cap one end of the cylinder at a time, see what affect it has on the drift, this should narrow things down for me correct? (valve vs cylinder) Anything else I should pickup to help with troubleshooting? I'm sure alot of you would suspect the internal relief and/or seals as that's the only thing i've touched, HOWEVER here's an added detail that may throw a wrench in it all: So alot of you pro mechanics may look down on this, but here's my procedure; when resealing the boom cylinder I left the barrel installed on the machine, and just removed the rod assembly. After removing the rod pin, I fully extend the cylinder and then shut down the machine. Bleed the pressure by moving the lever back and forth and begin to loosen/remove the gland. Once its free I crack the bottom hydraulic line (to allow air in) and pull out the rod assembly out. What i've done in the past for tricky/heavy rods that won't come out (like this one), is get a second guy to start the machine, and slowly extend the cylinder with the controls while I support/pull out the rod, pushing it out with the machine hydraulics. When we did this this time, as soon as the machine started, it started to push oil and extend the cylinder on its own, without touching the controls! Luckily I was right there holding the rod and my assistant was able to shut off the machine before too much oil was lost. Is this normal behaviour? Does it need some backpressure from the other side of the circuit to work properly? Is this an open center vs closed center situation?? I am no hydraulics expert, however in my years of using and fixing equipment I have never seen such a situation. I am imagining a busted hose in this situation, hydraulic oil would just continue to be pumped out until the machine is shut off. This is the one reason why I'm kind of leaning towards an issue with the control valve. Any help/insight/guidance would be much appreciated!
To minimize oil waste I always remove both hoses from the barrel, and if I can't pull the rod out by hand I put a strap in the rod eye and pull it out with my truck trailer hitch. From what you describe ---" the problem didn't exist until you put it back together" - then the relief valve in the gland is probably the problem. Or part of the problem. Did it take much effort to insert the rod with new piston seals ? Only the 580K's had a series 3 in their production line up. I'm not aware of a 580SK series 3.
Thanks for the quick reply Tinkerer. Yes it was quite tough to get back in as well as out, although I was thinking the cold during install (2-3 °C) and the oil being pretty thick would not help. I ended up using a ratchet strap through the rod eye and wrapped around the bottom of the cylinder to "pull it in", along with me helping it in. Lines were cracked to allow air/oil out. It is a 580 super K, I just assumed thats what people reffered to by "SK"? I really do not know much about these machines. Please enlighten me. This is first time i've worked on a backhoe. Just through my research I found that there was a series 1 and series 3 (what happened to #2 lol?) The owner said this one is a mid 90s. Like I said the shifter is on side console (series 3) not on the floor (series 1). Any ideas on testing the internal relief, or the fact this machine pushes oil without operator input? This time I think if I have to dissassemble I will pull out the whole cylinder so I can work in heated shop...
Part of the reason it shot out as you turn it on is probably when you had it off and we’re relieving pressure, the spool stuck in the extend a little bit as the spring center is a little weak. This could be the same reason it is dropping. I don’t think you damaged that relief but you know how much heat you put on it, we don’t. I have done that cylinder on my 580SE and I heated that bolt up dull red to get it off but putting it on off a quick set up staging, I dragged the seals across the threads quite a bit and ended up with the same issue. Thankfully I didn’t have to take off the piston, just replaced the dragged seals and I did touch up the metal cause I scraped that pretty well. Tha angle was a real pain to get in right.
Yes that could be a possibility. You are absolutely correct very much a pain to get lined up properly when that cylinder is angled upwards, and that rod is pretty hefty. I had to heat it up till the surface starts to turn blue. I used straight propane not oxy-fuel. Roughly 450 °f surface temp to get that lock tite loose. I have done this lots in the past with no ill effect but never had to deal with a piston with a relief in it before. Even with that and a 12' cheater bar it was a bear to come off. Anyone know how that relief works? A ball with a spring? Does it work in both directions? I'm starting to think if I heated it that much, and it has a spring inside I may have annealed or broken the spring in both cases rendering it useless... Thinking after I do the cap test, if the cylinder fails i'm just gonna bite the bullet and pull the whole thing into the shop. You're right the one upside is I dont have to remove that bolt to change the relief and/or seals again...
UPDATE: So spent an hour or so today doing some troubleshooting. Didn't wanna overthink too hard so I just tried a bunch of different combinations and am now looking over the results, please follow along as I unpack and feel free to point out something I may have missed: 1. Capped bottom (extend port), removed support; cylinder retracted under weight of boom. 2. Capped top (retract port), removed support; cylinder retracted under weight of boom. 3. Capped both ports, removed support; cylinder retracted under weight of boom. 4. Hooked lines back up, used boom to lift up back of the machine in the air. Cylinder holds, no sag. So looking at this, especially #3 smoking gun, tells me 100% issue is in cylinder. The only one that really gives me pause is #4. If the piston seals were bad there's no way it would NOT sag in this case correct? Surely the forces/load involved here are greater than that of lifting the boom in the air? This leads me to the conclusion the internal relief must be bad correct? It has failed in such a way that it holds pressure on the piston side (extend) but not on the rod side (retract). Priced out another relief valve, aftermarket wants about 300$ CAD, and 2-3 weeks away, assuming seals are still good, not a cheap chance to take, would hate to get it wrong. Plus waiting 3 weeks for part, only to be in the same boat but with worse weather. Does this all sound kosher? My brain sorta hurts after thinking about this too long, would love a second opinion on all this. Thanks
How was the internal bearing sleeve and did you replace it. This is the black thin sleeve that fits inside gland with an angle cut. Second question, how hard did the gland go on the rod? Third, when you said it holds machine in air fine, was it running the whole time or did you shut it down at all?
Yes, It sounds kosher. Like Tinkerer said " the problem didn't exist until you put it back together". It has to be the relief valve. "#4. Hooked lines back up, used boom to lift up back of the machine in the air. Cylinder holds, no sag". If the piston seals were damaged the boom would never hold the machine up. Cut the sidewall out of a plastic milk jug. Lay just enough of it to cover the lower half barrel threads. You will never damage piston seals by doing that.
Everything was replaced when I had it apart. The bearing or bushing was in good shape; really all was in good shape aside from the fact the wiper was gone (dry rotted away) and the two gland seals (u cup seal and the "grooved one") were also just very old and on the "crispier" side. Piston seals and bushing were also in good shape, but again everything was replaced. Rod itself is also in really good shape, no knicks or scratches. I would say gland went back on the rod well, not too hard not too easy. Lube everything up, get the wiper seal started. A few taps with a rubber dead blow and once its half/three quarter on I pushed it on. Then could slide it on the rod with a fair amount of force. I held it in the air with the machine running; I never even thought of shutting it off! (d'oh). Will definitely be trying that and report back.
UPDATE+SOLVED: Thanks to all who contributed their information and knowledge! SHORT ANSWER: it did indeed end up being the internal relief valve, likely due to me heating up the piston to get the bolt off. FOR THOSE LOOKING FOR MORE INFORMATION/HELP IN THE FUTURE: Hopefully this can help someone at some point. I attached pictures of the brand new relief (first 3) as well as the piston and where the relief is located (4 pictures on next post). It works very simply; in an over-pressure situation, oil will push against a spring loaded cone through the end orifice (picture 3) and allow the oil to pass through to the side orifices (pictures 1+2). This effectively bypasses the piston seals, oil passes from the rod side to the piston side, again SHOULD ONLY occur in an over-pressure situation (i.e. more than the spring can handle). In the other direction, (piston side to rod side), oil should not be able to ever pass through; the oil pressure should push the cone into the seat, the higher the pressure the "tighter" should be the seal. Having said all that, and thinking about the situation I was having, this makes perfect sense. In the retracted position (pressure on rod side, boom in the air) the oil was passing through the relief to the piston side, causing the boom to drift down. In the extended position (pressure on piston side, boom pushing down, even lifting the back wheels off the ground) the oil was pressing the cone into the seat, absolutely ZERO drift, the piston could easily hold the back wheels off the ground, even with the engine off. This test here essentially rules out the piston seals.
CONTINUED: Here are more pictures, of the piston itself, as well as where the relief is installed. 2nd picture shows where relief screws in (FYI takes an 11/16" socket with a thin wall to fit). 1st picture shows hole (larger hole, RH side) on rod side where oil has access to the relief valve end orifice. Last two pictures show another oil passage through piston, from the rod side to just behind the first piston seal. Anyone know the purpose of this? To the best of my memory, I can't remember ever seeing this sort of setup before (definitely not on any of the dozen or so Case cylinders I recently worked on). I didn't wanna think too hard about how this may affect pressure dynamic and sealing etc. and am just gonna chock it up to lubrication for the buffer ring lol. I would be interested in hearing if there's anything else to it though. Next post will be of the dissection of the old relief valve and why it failed.
I did not see a relief valve. Is that only on the boom cylinder only?
Look closer at the photos. It is in the piston. #19. Backhoe Boom Cylinder | CASE Construction | MyCNH US Store Find schematics, manuals, specifications and diagrams for BACKHOE BOOM CYLINDER. Find genuine OEM parts for your needs. www.mycnhstore.com
Does the relief valve just pull off or attached
It is screwed in. There is also a circuit relief valve in the boom section of the main control valve. Quite common for them to fail in older machines. It is not sold separately. Buying an entire section is the only way that I know to get one. I recently bought an entire control valve because the RH stabilizer relief valve was leaking. This link is for reference only. Your particular backhoe may be different. Backhoe Control Valve, Boom Section | CASE Construction | MyCNH US Store Find schematics, manuals, specifications and diagrams for BACKHOE CONTROL VALVE, BOOM SECTION. Find genuine OEM parts for your needs. www.mycnhstore.com
After doing extensive research on the internet several months ago I learned that a simple standalone, double pilot operated check valve can be plumbed into a hydraulic circuit and function the same as the one that is built into the control valve that failed. At least I think it will. Someone correct me if I am wrong.