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aschubert
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I recently spent considerable time spelunking through these forums trying to find out how to fix the problem with my JD 3-point hitch not lifting any weight. Or only lifting slowly at full rpm. While my only tractor is a JD 4400 perhaps this will apply to others as well. I was not satisfied with the end solution in the troubleshooting guide being to replace the rock shaft control valve at $500 or more.
Bottom line: The valve can be disassembled and fixed if has not been damaged by something harder than the steel. And no springs are broken or seals destroyed.
The first time the hitch would not lift weight was about a year ago. I read here and learned after disassembly that the in-line filter screen (inside of part AM123226) is prone to breaking loose and going downstream into the valve. And so it did.
In the first picture I have named what I THINK are the valve ports based on studying the hydraulic diagram for the internals of it. I will refer to them that way here. If the names are incorrect someone can correct me.
In any case, once the cover was removed it was easy to see a bit of screen sticking out of the dump valve port (see second photo). That valve is spring-loaded from the inside. All I had to do was to hang onto the bit of screen with the needle-nose pliers and then press the valve pin inward with a dowel to dislodge it. I then replaced the inlet part, AM123226, with a new one with a screen in it.
I was quite pleased with myself, thinking the problem solved until the same symptoms reappeared this winter. I once again pulled off the rock shaft control valve. No bits of screen were visible sticking out. After pulling almost all of the valve apart and reassembling the problem persisted. In some desperation I decided to fire up the tractor with the rock shaft cylinder cover off. When I actuated the 3-point lift lever I got a feeble spray through the port that feeds into the rock shaft cylinder. After verifying the port was clear between the valve and the cylinder I started the tractor with the rock shaft valve cover off and again operated the lift lever.
I am now intimately acquainted with hydraulic fluid as is a good part of my garage. But I did discover that fluid was being pumped out the port on the side of the valve, the relief valve (I think) when it should not have been.
I had missed this valve on the first clean out. It is located under a plug that is overlapped by the large valve cap where a hex wrench goes. I thought it was a press fit but it can be removed with a little prying. First remove the large valve cap with the hex wrench fitting first. And there's the little gremlin (3rd photo). Again, this is a spring loaded valve so you just need to release the screen by depressing it inward a little.
Well, my first and probably over-long post. I leave it here as a trail of pebbles for someone else who might have the same or similar problem.
Good Luck.
Art
Bottom line: The valve can be disassembled and fixed if has not been damaged by something harder than the steel. And no springs are broken or seals destroyed.
The first time the hitch would not lift weight was about a year ago. I read here and learned after disassembly that the in-line filter screen (inside of part AM123226) is prone to breaking loose and going downstream into the valve. And so it did.
In the first picture I have named what I THINK are the valve ports based on studying the hydraulic diagram for the internals of it. I will refer to them that way here. If the names are incorrect someone can correct me.
In any case, once the cover was removed it was easy to see a bit of screen sticking out of the dump valve port (see second photo). That valve is spring-loaded from the inside. All I had to do was to hang onto the bit of screen with the needle-nose pliers and then press the valve pin inward with a dowel to dislodge it. I then replaced the inlet part, AM123226, with a new one with a screen in it.
I was quite pleased with myself, thinking the problem solved until the same symptoms reappeared this winter. I once again pulled off the rock shaft control valve. No bits of screen were visible sticking out. After pulling almost all of the valve apart and reassembling the problem persisted. In some desperation I decided to fire up the tractor with the rock shaft cylinder cover off. When I actuated the 3-point lift lever I got a feeble spray through the port that feeds into the rock shaft cylinder. After verifying the port was clear between the valve and the cylinder I started the tractor with the rock shaft valve cover off and again operated the lift lever.
I am now intimately acquainted with hydraulic fluid as is a good part of my garage. But I did discover that fluid was being pumped out the port on the side of the valve, the relief valve (I think) when it should not have been.
I had missed this valve on the first clean out. It is located under a plug that is overlapped by the large valve cap where a hex wrench goes. I thought it was a press fit but it can be removed with a little prying. First remove the large valve cap with the hex wrench fitting first. And there's the little gremlin (3rd photo). Again, this is a spring loaded valve so you just need to release the screen by depressing it inward a little.
Well, my first and probably over-long post. I leave it here as a trail of pebbles for someone else who might have the same or similar problem.
Good Luck.
Art
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