Hello, I've got a 1996 JCB217, generally in good shape, and it recently had a strange hydraulic failure that I'm trying to get my head around. The front end loader bucket curl, is malfunctioning. Specifically, when the control rod is in the valve-neutral position, the bucket readily curls down. When I move the controls to curl-up, it does curl up somewhat, but seems to run into some resistance, presumably pressure related since the amount it will curl up depends on how much I throttle up. Also, the ram hoses "wiggle" on one side when it loads up, though not the other, strangely enough, since the lines to each side are simply tee'd. (The hoses are pretty old and cracked on the outside due to exposure, and I've got new ones on order, fwiw.) I disconnected the rams on each side one at a time and since I didn't have any plugs for the hoses, I simply connected the two ports together, again, each side separately. Same result. The failure was rather sudden. Anyway, this is looking like a blown control valve of sorts, but I don't have any experience with rebuilding any of these valves per se, hence my post. Any ideas? Anything I can trouble-shoot to be more certain before tearing into the valve block? If I do tear into it, anything to be weary of in the process? Thanks in advance!
Here's the troubleshooting page. Could be: - clogged pipe/hose, but unlikely - ram not leaking - ARV? not familiar with its function - valve block section blown (no leaks, check valve? linkages are okay) - check valve, not sure on the function it - HBPV, not sure on the function of it - piston rod isn't bent (i.e. rams are fine I believe, and the valve control rod is fine too I believe, since the control rod seems to move the spool normally)
Here is the circuit. Rams 31 and 32 and the associated valve 3D with 3F,G,J 3D Loader Shovel Ram Spool 3F Shovel Ram Head Side A.R.V. 3G Shovel Ram Rod Side A.R.V. 3J Load Hold Check Valve
When they mention ram leaking it doesn't necessarily mean external leaks that you can see. Bucket creeping down is most often internal cylinder seals leaking. Might also explain why they react to more throttle/flow. If you put the bucket flat on the ground can you lift the front end by dumping the bucket? If so does it hold or does it also creep down? It may not be the cylinder seals but that's the 1st thing to rule out before getting into the valve.
Good point that it may be internal (and about the creep). I'm going to get some plugs and plug the hoses on each side and see if each ram works or not independently. However, since the thing literally/actively slams down in the neutral valve position, it seems like it's the valve. If I put it in "turtle mode" (switch), it doesn't slam as rapidly, which suggests that there is differential pressure in the neutral valve position.
A cylinder will still work with leaking seals. It probably won't have as much power but will still work. Only one needs to leak if they're tee'd together but if seals are required do both cylinders. The bucket cyl. seals went out in my skid steer and the bucket constantly fell down, worse with a load and I had to counteract it with the control valve. Put new seals in and problem solved. Old seals were noticeably bad.
As Melben routinely points out, use the rollback function on your loader to load up cylinders and check to see if one gets hot after being "bottomed out" for a while...
Looking at the hydraulics schematic some more, could it be that one of the check valves or pressure relief valves is stuck open somehow? I'm still not getting my head around what could possibly be off here, which is to say, I haven't deduced from the schematic some scenario that corresponds with the symptoms I'm observing. However, I don't think it's the primary spool. Edit: scratch that. 1) It could be that one of the pistons internally has a major leak. In that case, hydraulic fluid is pumping into one cylinder and flowing through it, whereas the other cylinder is working but it's limited by the hydraulic pressure since the leaking one is in parallel. I think this was suggested, and I just didn't understand it. I should be able to plug the hoses on either side separately and one or the other cylinder ought to work then (if both aren't blown). 2) If the "curl up" check valve or pressure relief valve is blown, the same thing should occur regardless of which cylinder I disconnect (assuming both aren't blown). 3) I could swap hoses between the curl and lift valve, and if I still get the same result then it's definitely the cylinder(s). Sound like a plan?
Yes, that's a solid plan. But as stinky said, the leak will heat up. Park the machine with the bucket against a large tree etc. wait until a cool morning with a heavy dew, start up the engine and immediately try to lift the tree at idle for thirty seconds, then shut off the engine and see if either cylinder is warm where the piston would be, or if the relief valve on that spool is warm or anything else on the valve is warm. If you do it just right, the part will be steaming like it's about to burst into flames. you can do it anytime the machine is cool, a thermal imaging camera makes it even easier, but not needed, you should be able to feel it, if not, run it another minute.
Luckily for you, in this age of covid testing, you or someone you know has a hand held digital infrared thermometer that just may be beneficial for this application
Well, to wrap this up, it seems that the guys that rebuilt the curl rams last (a big pro logging outfit around here, big CAT shop), screwed it up. A buddy of mine discovered the dirt seal on one ram was bulging out, so we pulled that ram and looped the hose. We discovered the primary seal also had a chunk missing, though not clearly all of it, and some of the other seals were a little torn up. Nevertheless, I figured we could still get the other ram to respond the same as I'd been seeing. So we took the load pin out the second ram, fired it up, and it literally shot the piston rod OUT of the other cylinder. In fact, what had happened is the piston had UNSCREWED itself from the rod, and that was definitively THE leak. As it turn out, the threads are all jacked up on the rod, so I need to have a word with this place. There is a pin in these that is supposed to work like a set screw but more definitively to keep this from happening, and that pin is missing from both rams. Fortunately the piston and the cylinder walls look okay, maybe needs the threads chased slightly if anything. The good news is it appears that there's no problem with the valve/spool, excepting that there might be some bits of seals and whatnot that may at some point jam up something. Fingers crossed for now.
Sounds like the place had absolutely no experience with JCB cylinders.
This says it all. DITTO!
Or any kind of cylinders. Leaving the set screws out is idiotic.
Would you say there is anything particular about JCB cylinders that one should be aware of? Likely I'm going to fix this one myself.
I'm not familiar with JCB cylinders but it is very apparent the place that worked on them knows less about them than I do.
Don’t match up seals. A genuine kit from JCB will last much longer. I had trouble trying to match up due to their oddball sizes.
LOL!
I’ve done some JCB backhoe cylinders... I think they are some of the easier ones to do. Like others said, you just need to pay attention to the dowel that is under one of the wear rings. The dowel takes a small metric bolt to just pull it out. Then on installation, I just thread the piston On until the dowel holes in the piston and the cylinder line up. Sometimes takes a little time to line them up since they are pretty tight tolerances. I have had good luck with seal kits off eBay, but if you had a dealer close I would probably try for OEM.