3-Point Hitch JM-304 TPH Problems/Questions

Rich Waugh · May 28, 2011

I have an issue with my TPH that I'd like some guidance on. My 2007 304 Jinma has the single-lever control for the lifter; top half of the movement is position control and lower half is draft control. That's all well and fine, I understand the difference and applications thereof, but the position control is a bit too arbitrary to suit me.

If I have the bush hog on and want to raise the hitch up I have to pull the lever nearly to the top of the travel just to get it to initiate movement, then it goes right up. When I want to lower it to cut, I have to drop the lever nearly to the bottom (of the position control portion) before it even starts to drop, at which time it goes down pretty much all the way. I can finesse it into the position I want by going back and forth until I get lucky, but that isn't really too handy, you know? I'd like it to be more "linear" in action (more determinate, so to speak), so that when I move the handle a little bit I get a little bit of TPH movement - in a predictable way. Not this random chance routine I have to use at present.

So, what's the answer? Do I simply need to adjust something, or what? I'm thinking the lift cylinder itself is okay, since it stays up when it's supposed to, even when I'm bouncing all over on rough trails. Is there something that needs to be done to the control valve for the TPH?

I'd like some advice before I just blunder into this, since I'm not a wizard with hydraulics - I understand the general theory of hydraulics, it's the actual practice I'm weak on. In theory, there's no difference between theory and practice - in practice however, there usually is. :mur:

I await your wisdom!

Rich

greg_g · May 28, 2011

Yeah, sounds like a control valve issue. My KM454 started to exhibit that very same problem, but it was so close to trade-in time that I didn't mess with it. If I still owned it however, I'd have started by removing and disassembling the control valve for a good cleaning.

//greg//

g0rd0 · May 28, 2011

I have a 07 284, on the deck in front of the hydrolic fluid resivoir in the middle is a thumb wheel by turning it left or right you can adjust the flow to the lift and that should solve your issues with the raiseing and lowering, it did for me. I hope this helps you

RonMar · May 28, 2011

Gordo, he has a different type control valve on his 304. AFAIK, the 284s don't come with position control, just a basic control valve with a height stop linkage, and the speed reg valve you mentioned.

Rich
Your description of position control sounds right. If you want the impliment to come up 20%, moving the lever 20% up should accomplish this. To do this, the valve uses some sort of feedback from the piston movement, usually to maintain some sort of balance. IE: the actual valve is connected to a sliding mechanism that is moved by the piston. When you move the lever, you push on a spring that pushes on the valve lever, pushing the system out of balance. This moves fluid and the piston, which moves the valve back to a balanced position where it no longer moves fluid...

How this is done exactly in your case, I have no idea

But it sounds to me like some part of the internal mechanism has shifted, broken or otherwise developed slop, which has opened up the area where it thinks it is in balance/aligned with the handle. So you have to move the handle a long way to even get it to start to move.

If you have an exploded view of the control valve/lift mechanism, we may be able to point you to a likely area to investigate for problems...

Rich Waugh · May 28, 2011

Unfortunately Ron, my manuals show the old-style lift control with the two levers, not the single-lever system that I have.

I did some extensive fiddling with the flow control valve in front of the seat this afternoon and got it to where the implement drops a bit more appropriately and I can now finesse it to the desired position more easily and reliably. There's still a fairly wide range of lever travel between lift and drop, but the range has narrowed noticeably.

I can live with it this way, I suppose. I'd rather have the sort of accurate feedback loop control that you describe, however. Sadly, my knowledge of hydraulics is simply not up to the task of diagnosing and correcting that feedback system. I can fiddle with a knob okay, but the other stuff is above my pay grade.