3 ph drifts down

[jeff9366]

Jeff9366, The tractor is stored in a heated garage, has about 600hrs. on it, hasn't had the filter or fluid changed since what was recommended after the initial break-in period.

You do not actually say you have checked the hydraulic fluid level. Have you? It is time to change the hydraulic fluid and filter after 600 hours and 8+ years, that is for sure.

 

[3v0]

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.

 

[ScottyChip]

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.

 

[Leejohn]

While you have it apart make sure you check the 2 o rings under the control valve.

 

[sd455dan]

Ok I have lived with this for a couple years so now is the time to fix it! I have a 2004 Kubota B7510 HST and the the 3ph drifts down all the time! It doesn't matter if I am driving the tractor or if it is sitting running while I am doing something else. doesn't matter if it is at idle or full throttle. I have even been going down the road and tried to lock it in the up position with the knob in front of the seat. I am thinking it might be a seal on the lift cylinder. Any thoughts?? Thanks, Ken.

I had another thought after posting the information on the rockshaft seal.
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

 

[jenkinsph]

if it is like most tractors, the rockshaft seal if bad- results in your description, but the hydraulic control linkage would cause it to lift back up to the original position if the tractor had position control and the tractor was running..

When not running the quick lowering is the most common result with a failed rockshaft seal...one more thing a rockshaft seal failure will not affect fluid level, it will just end up in the sump..View attachment 313934 View attachment 313935as can be seen in this picture the cylinder that the rockshaft piston slides in is open to the sump, this ones seal had completely disintegrated.
Replacing the seal and honing the cylinder restored the 3 point lift, to as new operation.
You can also check your work by using an air compressor and an inexpensive leak down tester as I did, this assures you that the seal is sealing correctly and that it didn't get damaged during installation View attachment 313940 besides those rockshaft covers aren't exactly light, and it's no fun taking it apart twice...

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.

 

[jeff9366]

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.

 

[jenkinsph]

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.

No.
If there was not enough fluid the hitch might not raise fully or properly. The leaking down is a separate issue. I do agree that everyone needs to perform proper maintenance if they want good long term reliability and performance.

 

[600rider]

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.

 

[sd455dan]

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: