Is anyone saying that changing hydraulic fluid might help leak down ? I can see this helping if the tractor has the wrong type fluid in it. Not so sure if you replace the fluid with the same type.
Hi 600Rider, my Kubota 7510 is the same, the 3pt hitch drifts down, in my case it will drift down faster when the rpm's are at or just above idle and very slowly at 2000 or higher. It is a pain. I am considering the repair this summer, I think that Sd455dan in post #10 hit the nail on the head, the seals on the Hydraulic piston/lift arm are bad and need to be replaced. I am attaching an image from the parts manual I found showing the piston (#010) and the O ring (020) with Ring back up (030) are the parts I am going to need.
The knob under the seat will not lock the 3pt in position if the seal is bad, the hydraulic fluid will bypass the control mechanism. Hope this helps.Attachment 313938
While you have it apart make sure you check the 2 o rings under the control valve.
If it is designed to where a small cover can be removed, like the pictured unit- that has a direct feed to the rockshaft cylinder it may be possible to test the cylinders leak down directly- without tear down...
By accessing the direct port and then doing a leakdown test...if the cylinder is not leaking it could be o rings- but the test might nail it down without a full tear down hope this is helpful
I agree with this post^^^^ most likely the rockshaft seals are shot. The next possibility is the rockshaft valve is leaking and would need new orings too.
While it is a good idea to make sure you have clean fluid I don't see where this would be related to the problem at hand.
To this point, the OP has NOT told us he has checked the fluid levels.
Hydrualic fluid may be at 40% of "full" level, causing the problem.
This would not be the first time someone has 600 hours on a tractor and has never checked the hydraulic fluid level, much less changed the hydraulic fluid and filter, and wondered why the equipment is not operating normally.
Yes I do check the tractor over on a regular basis. I check all fluids and belts tires and such. I think that if there wasn't enough fluid it would not raise at all or intermittently. I think my problem is the o-ring on the lift cylinder and have ordered the parts. I also will be changing the hydraulic filters and cleaning the screen. I will check the fluid but doubt I will change it as super udt is priced like gold! Thanks all for the help, Ken.
One other thing 600rider , and you may already Know this, but I did not think it would hurt to include it.
The main piston seal is a v type seal it will always be installed with the outer sealing lip facing the pressure side of the oil circuit.
That way as the hydraulic pressure increases the lip of the seal will be pressed outward and in contact with the cylinder proportionally to the pressure of the fluid, so the higher the fluid pressure, the the tighter the lip presses outward.
The tractor I replaced the seal on only employed one seal, and as you stated- your application requires a second seal... not sure if the back up seal is of the same type so can't advise on that ... Looks like your well on your way to getting the 3 point back to fully functional :thumbsup: