Hi i have a JD 892ex. The issue im having is the bottom pilot control cap is cracking at the function for the thumb. The thumb control is from the toggle switch on the joy stick. For what ever reason if you do 2 functions l, like boom up and move the thumb at the same time the pilot line to the thumb function spikes to 2500 to 3500 psi briefly and then cracks the cap. I checked the plumbing for the thumb pilot pressure and its pluned correctly. When you operate just the thumb the pilot pressure remains around 400 psi or so. Could the main valve body be cracked and feeding back or something. These caps are becoming rare and expensive and my problem and I need to fix this Thanks
How about a machine serial number? The pilot systems are laid out differently depending on the serial. Is your thumb pilot plumbing a foot pedal or a switch on the lever?
Please see attached serial number. Thanks
Has any other spool pilot been checked top see if it rises also?
Yes other functions dont spike. The opposite end of the thumb function (top cover of the spool) spikes but hasn't broken amd doesnt spike as high
Is this a new issue on an old installation, or was the thumb recently installed?
The thumb was a new addition to the machine about 4 years ago. This issue has been happening since installed. It lasts about 3 months before it cracks the cover
Seeing as the cap has cracked multiple times since the thumb install and you state the pressure increases with multiple signals, I am guessing that there is a internal crack in that valve body. Do you have a hydraulic schematic of the valve body? You shouldn’t see those kind of pressures, unless there is back feeding, beyond any check valves or pressure relief valves.
It makes me wonder about the installation?
This should be what you've got. If you haven't already, it would be a good idea to try separating the pilot lines from your attachment spool with your gauges plumbed in to confirm that the high pressure is actually coming from the control valve and not the pilot system. System pressure can enter the pilot system from the flow combiner valve. The symptoms don't really match what you're describing but it's somewhere to look. Also, not having orifaced ports in your DO1 valve that actuates your attachment spool will cause spool caps to break from the spools shifting too fast/hard. Again, doesn't fit with the high pressure your reading at your pilot lines but its something to consider if you're not 100% on your troubleshooting
So to separate and test, if I take the pilot line going to the spool cap that cracks and put a gauge on it, dead heading it? And work the two functions and look for the spike in line pressure. ? If it spikes it would eliminate the issue being at the spool end and could be coming from elsewhere ? Does that make sense?
Hi its on a switch on the joystick
Yes I have checked others and they do not spike
So behind the cab theres a electric over hydraulic valve that is controlled by the thumb switch on the joystick which works the thumb pilot signal. I followed those hoses to the main valve body. It all looks like a factory install
I'd put my -6 run t with the gauge on it on the spool cap where you saw the 2,500 psi and re confirm that reading. Then id leave the run t on the same spool cap and cap off the pilot line and see if you can get the same pressure reading or not. Lastly id plumb the gauge back into the pilot line, without the spool cap attached and see what pressure you get. If you cant get the pressure up to your 2,500 psi you saw in step one, it may be that the spool itself needs to be shifted to allow the high pressure oil into the spool cap, so id use caution and try to figure out another way to confirm where the oil is coming from. Id also spend some time playing around with step one, and reconfirm that both attachment and boom 2 only need to be stroked to get the high pressure. And also, once the pressure spikes, does it drop off Once you let off boom, or let go of thumb, or do you need to let off both? Also, does it act up with the thumb in both directions, boom in both directions?
Thats your D01. There should be oriface fittings in the A+B fittings, in the sub plate, or in the 2 fittings in the spool caps. But thst being said, no oriface fittings wont cause a pressure spike like your seeing. I would trace the hose out off the P port and make sure its coming off a pilot source and not from the control valve or a pump though
Thats kinda what I was thinking. So I will re do it all tomorrow and see whats going on again. I can confirm that it spikes in both directions but the pilot line on the top side of the spool valve only hits around 1500ish. The bottom one gets the higher numbers. I Will confirm all tomorrow. Thanks for the help
I will re check where the lines come from tomorrow. If I recall they were t into the pilot lines in the cab. But I could be mistaken
No sweat, and good luck. Im really curious where the pilot supply for the D01 is coming from.....
Usually it gets T'd off a pilot supply hose under the cab.
This is the kit that should have been installed. Fitting #27 should be an orifice fitting. You only need one on one side. It will cushion the spool movement in both directions. Otherwise, follow what @Johhnycanuck is directing you to do. He is leading you down the correct path.
Im curious if you found anything with this?
Hi. Sorry for the late reply. Thankyou for the help! Ive been very busy. Yes I figured it out. Someone Td the pilot line into the test port on the right pump. The line with the red cable tie, goes under the cab to a mess of lines and ts. Everthing makes sense now. I will use the diagram in this thread to plumb it correctly.
Good deal, im glad you found it and thanks for the update
I know where the hose bulkhead under the cab is. Which one is the pressure in that i t from?
Tee into the pressure supply line to the foot pedals at the pilot shutoff valve under the cab.