3-Point Hitch Farm Pro (Jinma) 2425 hitch will not stay up

[robmc5]

Hello again, I have a Farm Pro (Jinma) 2425 that the hitch will not stay up. There is a adjustment knob under the seat that controls the rate of drop ( I think) and if I tighten it all the way the hitch will stay up, but then it will not drop. I just had it serviced and it did not seem to stay up after the service job. I have talked to the shop that serviced it and they just want me to bring it back, but that is no easy task. Does anyone have any ideas that I could try to resolve this?

Thanks again guys, this is a great forum!!

Rob

 

[RonMar]

If it stays up with the speed reg valve closed all the way, the problem is not the rings in the piston, it is the control valve. The fluid from the pump goes into the control valve and then on into the reservoir. When you command the valve to lift the 3PH, it diverts the flow from the reservoir to the cylinder. It flows by a relief valve and thru that speed reg valve along the way. When you command the valve to lower the 3PH, the fluid flows back thru the speed reg, past the relief and back thru the control valve and into the reservoir. If the relief is leaking past, this would cause the 3PH to fall on it's own, or if the control valve is leaking past, it would also cause this.

Here is a link to a valve diagram on johns jinma website.
http://www.johnsjinma.com/files/HydValve.jpg
The relief is located on the top of the control valve body toward the front. It is under a square headed screw-in plug(part 1 in this pic) that holds a spring and stacked washers down on top of the valve body. The combination of washers and spring sets the relief pressure. It is easy enough to pull all the parts out and make sure that there isn't a piece of crap holding that valve(part #5) open a smidge.

Or the main valve bore could be worn allowing fluid to leak back past the spool allowing the 3PH to creep down. My bet would be on the relief being stuck, if not Affordable probably has the valve on the shelf...

 

[robmc5]

Ron, thanks for the reply. I definitely will check the relief value, I found some other posts from you that talk about getting a rebuild kit for the 3PH. I did find a manual online at

http://www.jinma-tractor.com/download/JINMA20-30A.pdf

My first inclination is to make sure the stop block is in the correct position, does it have anything to do the 3PH dropping? Its way far back on the rod and I am not sure if they moved it when servicing the tractor. As far as the relief valve, is that the same valve I use to adjust the lowering speed?

The funny thing is that it worked fine before I took it to get serviced. When I got it back I raised the 3PH and then it would not lower. I turned the lowering valve and it lowered, but never would stay raised after that. I have only put about 10 hours on it since I got it, 785 hours total. This is my first tractor and I really appreciate the help.

 

[RonMar]

The stop rod dosn't have anything to do with lowering, it simply kicks the control lever back to neutral. On older tractors, if it was misadjusted the 3PH could lift too far and damage the seals on the piston, but you have already proven the seals on your piston are OK. I don't think this is an issue on later models as they(Jinma) fit an internal stop block to the inside of the rear cover plate that physically prevents the piston from extending too far out of the cylinder when lifting. My 2005 model has this stop inside the reservoir.

The relief valve assembly is ON/a part of the 3PH control valve located under the right side of the seat. the control lever connects to the valve. If the shop that serviced it checked the relief pressure of that safety valve, a piece of debris may have found it's way into the valve at that time.

I should have suggested that you flush the valve yesterday which may fix the issue right there. This is easy to do without disassembly of the valve. Screw the speed regulating valve knob all the way in till it is tight, then start the engine and try and raise the 3PH. The hitch should not go up as you are blocking flow to the cylinder. This forces the relief valve on the control valve to open and forces fluid thru it. This may clear any debris in the relief and restore normal function...

 

[robmc5]

Ron, thank a lot for the help, especially the diagram. I finally got out to work on it yesterday and tried to flush it like you suggested, but that did not help. I did pull what I think is the relief valve (the front plug) and found a few things.

Here is the cap I took out.



I noticed that there were some washers in the cap on top of the spring, it got me thinking that maybe the spring is worn and not allowing the valve to close all the way. There were three washers, I had some of the same and I added two more this did not help, also I removed them all, this also did not help. Here are a few more photos.



I don't know that much about tractors (nothing actually) so I really appreciate your help. I would like to fix this myself if possible, the tractor was working fine until I had it serviced. Am I on the right track? any other suggestions?

I am going to pull the rear plug out this afternoon and see what it looks like.

Thanks again
Rob

 

[RonMar]

Yep, that is the relief valve. The relief pressure is set by the combination of spring and stacked washers, so at the very least, it you should re-assemble it with the original washers in place. You need a pressure gauge in the system to properly set the relief pressure. In your second picture you can see the valve plunger on the end of thepart you indicated as the spring. That plunger rests down on the valve seat and the spring pressure causes it to seal against the seat. This seal should be maintained untill the pressure under the plunger exeeds the spring pressure and the fluid pushes up and past the plunger to escape back to the reservoir.

The hole was probably full of oil, you need to get the oil out so you an see down into the hole and make sure the seat is smooth and clear of debris so the plunger will seal on it.

There are only really 3 ways fluid can leak out of the system. like I mentioned earlier, 1. is past the sealing rings on the piston in the hydraulic cylinder. You eliminated these when you closed that speed reg valve in front of the seat with the lift in the up position and the cylinder didn't leak down. 2. Is past that safety relief which you inspected. 3. Is back past the control valve. The control lever has 3 positions, Up, Down and a detent position that holds the valve in the middle. In the middle position fluid should not be able to flow back past the spool(the sliding plunger/rod in a hydraulic valve) in the control valve. Are you certain the control lever is staying in that center detent position? That rear cap has another spring that pushes down on a ball bearing that rides in the notches that hold the valve in one of the 3 positions I mentioned above... Here is a hydraulic drawing that might help you get your brain around the flow. The fluid enters the control valve and passes right thru to the reservoir untill you divert it to lift the 3PH. It passes the relief(REL) and the speed reg valve on it's way to the cylinder.

 

[robmc5]

Ron,

Thanks again for all the help on this problem. I will pull the back valve this week (maybe today) and see what it looks like, I will post more pics if I see a problem.

 

[robmc5]

Ron I pulled the rear valve out yesterday and here is what I found.


I dont know if this is the correct valve, its the one behind the first pics I send and above the lever. I removed the bolt and there was a large washer and the spring, there were no small washers above the spring like the other one. I pulled the spring out and cleaned it and tried to removed the cap, but I could not get it out. basically I got out parts 24/25/26 in the diagram. I could not get 22 or 23 out. it looked clean from what I could see. Do I need to disassemble it further? I did put it back together and still the 3PH would slowly drop when it was raised and in the center position. Here are the parts I removed -



I have one other question, I purchased a new fuel gauge. There is a green ground wire and a red and yellow hot, I connected them with red to the center post and yellow to the side post on the gauge. The ground connected to a wiring harness under the dash (same place as the missing gauge bracket). The new guage did not work, I test volts on it and there was nothing, Either there is another problem or the ground is wrong. Do you have any experience with this? I know... I really need a manual.

Ron, thanks again for all the help. I would love to send you a 12 pack!!

 

[robmc5]

Ron, I took it to a local John Deere shop here and they took the relief manifold apart, and pulled the piston. They also replaced the oil and a couple of O rings. They reassembled it and its still doing the same thing. They really had no explanation (except that they had never seen that type tractor before, lol) I found some drawings of the hydraulic system but there were way different than my tractor.

Any suggestions would be appreciated!!

 

[RonMar]

Well if it still stays up with a load on it when the speed reg valve is screwed closed, the piston/cylinder and seals are not at fault. The control valve is obviously leaking by either past the spool or past the relief in the valve body. It may have an internal crack, casting flaw or machining error. I would replace the control valve. Affordable should have them at a reasonable cost...