Help with 3-point hitch repair

[Roll]

1997 Kubota B7300 HSD, 4 wheel drive, 3 cyl diesel (16 HP); SS: 12477 with Front End Loader Model: Kubota LA272 SS#: 12260; and Kubota Rotary Mower Model: RCK54-24B SS#: 32831 (New) Installed 4-18-17

Hi Folks, been a while since I dropped by.

I'm looking for some help with a refresh of the 3-point hydraulic cylinder. With nothing connected to the hitch it will drop to the floor overnight by weight of the two arms alone. I suspect the O-Ring and maybe the backup ring as well.

I looked through the Workshop Manual and find the Hydraulic Cylinder addressed on pages 8-58 and 8-59. Seems like a fair amount of work for a handful of instructions.

I planned to service the piston only and then reassemble without tearing down the entire assembly. FYI I serviced the hydraulic system last winter with a new filter, new screen, and complete hydraulic oil change.

Can anyone offer tips, suggestions, warnings? Should I expect to hone out the cylinder wall? (Would need to get a honing tool.)

Thanks for any help offered.

Roll

 

[Kubota Newbie]

If I had $10 for every tractor that the 3 point arms leak down on over night I could pay back everybody that lost $ in the stock market the last two weekdays.
Is it really that big of a problem? It might not be the cylinder, could be control valve, the safety/bypass valve, or (less likely) something just out of adjustment.
If I had one that was leaking bad enough that it had to keep hiking itself back up because of leak-down while in use I'd probably fix it. But if it is only an overnight thing then I don't know I'd bother.

 

[North Idaho Wolfman]

Most of the time they just need new rings, but you won't know for sure till you open it up and see what it's condition is.

 

[Roll]

hydraulic piston-coat O-ring with trans fluid

Dealer suggesting I coat the new O- ring with trans fluid to soften it up and assist with installation to avoid nicking or damaging it.

Made sense to me but I got the impression he was suggesting automotive transmission fluid, not the Kubota's HST fluid in my B7300.

Is that usual, to use ATF for a car to soften the hydraulic piston ring a little?

Roll and thanks in advance.

 

[North Idaho Wolfman]

Re: hydraulic piston-coat O-ring with trans fluid

I think this is a preference thing.
I heat up the O ring and stretch it a little and use hydraulic fluid not the ATF.

That will make it slide into place instead of grabbing and micro tearing and nicking the surface.

 

[Yooper]

Re: hydraulic piston-coat O-ring with trans fluid

I like to use the same oil that the O ring is going to be sealing. A little deburing with Scotchbrite around the end of the cylinder is a good idea also.

 

[Roll]

Re: hydraulic piston-coat O-ring with trans fluid

I think this is a preference thing.
I heat up the O ring and stretch it a little and use hydraulic fluid not the ATF.

That will make it slide into place instead of grabbing and micro tearing and nicking the surface.

Thank you both; very helpful.

Roll

 

[Roll]

Interim report on 3-point hydraulic refresh

If anyone is considering doing this on a B7300 or similar Kubota, a couple of things to note.

After twenty years the bolts that hold the hydraulic controller assembly to the base became corroded, I was lucky they didn't snap off. I am using new replacement bolts when I reassemble.

The linkage is a pain to get loose and out of the way. Same with the delivery pipe, I used a 1X2 length of board to hold it back out of the way.

I needed a two foot breaker bar to loosen the top link bracket bolts.

The most difficult connection was the Fulcrum shaft and its controls. I ended up pulling the controller assembly off so that I could slide the control lever off the shaft. Awkward but it worked.

I was told the casting weighed 60 pounds, not true, I weighed it on the bathroom scale, it weighs 42.8 pounds. That’s still heavy. I used a piece of nylon rope tied to all four corners to lift it off the housing and carry it over to the work table.

Planned to remove one arm to slide the shaft out of the housing with the other arm but realized quickly I was not going to be able to pull the arm off the spline. I gently knocked out the retaining pin on the (interior) hydraulic arm and then lifted the rod out. Finally, the piston came right out with a brief pop of air in the controller forward hole. Watch out, it comes fast, be ready to catch it with something soft. Mine nearly fell to the concrete floor.

Pictures attached if you are interested.

Question for the knowledgeable techs... looking at the piston pic, you can see marks (grooves) at the top of the pistons side wall and near the bottom. I see the same type of marks in the cylinder, no pic. I also see in the pic some nicks in the o ring. With the o-ring and retainer located near the middle of the piston I wonder if it rocks/pivots in the center and so, the top and bottom edges of the piston brush against the cylinder walls as it goes up and down?

Is a new o-ring and retainer ring going to make a difference? I don't see myself replacing the entire casting and I'm not too anxious to attempt to hone the cylinder. Thoughts/suggestions?

Thanks all, Roll

 

[wdlanning]

Re: Interim report on 3-point hydraulic refresh

What were your symptoms before you started and are
You opening up the control valve?
Excellent pics and narrative

 

[Mark15]

Re: Interim report on 3-point hydraulic refresh

Thanks for the pics, its nice to see how those are assembled. No experience with a 3-point cylinder, but I would assume the same principles apply as with an engine cylinder.

Often scratches are hard to gauge visually. When you drag a fingernail over the surfaces (both piston and cylinder) can you feel the scratches? If so, is it barely discernible, or a very noticeable catch of nail?

One advantage is these only stroke up and down when you tell them to, so the wear on the piston / cylinder should be WAY less than on a typical engine that strokes 1,000+ times a minute.

Did the 3 point hold position when raised with an implement and then have engine shut off? If so, I think that would indicate a leak down in the piston. the feedback position control would probably auto-correct and hide this when the engine is running.

EDIT: If there was a leak down when shut off in raised position, it could also be due to leaky spool in the control valve, or anywhere else on the pressure side of that hydraulic circuit as well. Piston is just one possible cause.

 

[Roll]

Re: Interim report on 3-point hydraulic refresh

What were your symptoms before you started and are
You opening up the control valve?
Excellent pics and narrative

Bought this 1997 B7300 (1500 hours) in Nov 2016. With the tiller (350 pounds?) on the 3-point, the hitch would drop a couple of inches over the period of 2-3 hours. At the end of the summer 2017 (now about 1535 hours) the hitch drops from its highest point to the floor over night and that was without any attachment, just the weight of the 3-point lower arms.

I have not decided if I will disassemble the control valve. I had to remove it to get the piston out and will replace the two small O-rings when I reassemble. Not sure I want to open it up.

 

[Roll]

Re: Interim report on 3-point hydraulic refresh

Thanks for the pics, its nice to see how those are assembled. No experience with a 3-point cylinder, but I would assume the same principles apply as with an engine cylinder.

Often scratches are hard to gauge visually. When you drag a fingernail over the surfaces (both piston and cylinder) can you feel the scratches? If so, is it barely discernible, or a very noticeable catch of nail?

One advantage is these only stroke up and down when you tell them to, so the wear on the piston / cylinder should be WAY less than on a typical engine that strokes 1,000+ times a minute.

Did the 3 point hold position when raised with an implement and then have engine shut off? If so, I think that would indicate a leak down in the piston. the feedback position control would probably auto-correct and hide this when the engine is running.

EDIT: If there was a leak down when shut off in raised position, it could also be due to leaky spool in the control valve, or anywhere else on the pressure side of that hydraulic circuit as well. Piston is just one possible cause.

Most or the marks I can see but not feel. There are a couple that I can detect with my nail but they do not seem to be deep.

I had some drop while using the tractor (I think) but my concern was that the tiller and later, the two lower arms, dropped when the tractor was parked and turned off.

Yes, I'm aware it could be one of several things, but I gather more times than not, it's the piston rings. Still considering pulling the control valve apart but concerned I might not reset it properly.

 

[North Idaho Wolfman]

Re: Interim report on 3-point hydraulic refresh

I have not decided if I will disassemble the control valve. I had to remove it to get the piston out and will replace the two small O-rings when I reassemble. Not sure I want to open it up.

Taking it apart really won't do you any good, there is nothing that is replaceable /repairable inside the valve.

 

[Roll]

Re: Interim report on 3-point hydraulic refresh

Taking it apart really won't do you any good, there is nothing that is replaceable /repairable inside the valve.

Thanks Wolfman, I have checked and to replace the valve is expensive. About $400 as I recall. I'll just reinstall as is.

... except for one puzzling thing. The diagram shows a snap clip on the parts drawing. It is missing on my valve. I have ordered a replacement clip. The local dealer seemed to think it might be at the bottom of the differential case. I have considered fishing around down there with a magnet.

Is that a thing? The snap lock pops off and drops into the oil below? If it had been caught up in the ring or pinion gears you would think I would have heard it.

Roll

 

[Dave_eng]

Re: Interim report on 3-point hydraulic refresh

A short time ago I posted some details from Kubota about the correct orientation of snap rings.

It might be of interest to you. Post #9

http://www.orangetractortalks.com/forums/showthread.php?t=34633&highlight=snap+ring

Dave

 

[Yooper]

Re: Interim report on 3-point hydraulic refresh

Maybe an engine rebuild shop would hone that cylinder for not that much money. As long as you're this far it would be worth it in the long run to give you decent life on the O ring.

 

[Roll]

Re: Interim report on 3-point hydraulic refresh

A short time ago I posted some details from Kubota about the correct orientation of snap rings.

It might be of interest to you. Post #9

http://www.orangetractortalks.com/forums/showthread.php?t=34633&highlight=snap+ring

Dave

Huh! Never occurred to me. At first I thought that had to be wrong then it gelled. With the rounded edge facing away from the direction of force, force could actually cause the snap ring to spread and ultimately fall off. That's really interesting.

Thanks,
Roll

 

[mikkeeh]

Re: Interim report on 3-point hydraulic refresh

Just curious....If the 3 pt drops completely overnight....what problems does this cause? I guess I don’t see an issue.

 

[Dave_eng]

Re: Interim report on 3-point hydraulic refresh

Huh! Never occurred to me. At first I thought that had to be wrong then it gelled. With the rounded edge facing away from the direction of force, force could actually cause the snap ring to spread and ultimately fall off. That's really interesting.

Thanks,
Roll

Glad it enlightened you.

It is always the little details that make the most difference

Dave

 

[Dave_eng]

Re: Interim report on 3-point hydraulic refresh

Replacing the O ring and backup ring with new Kubota parts is likely all you need to do.

Note there is a proper relationship between the two rings.

Don't go using any O ring just because it fits. There are many materials O rings are made from and this greatly affects their performance. Those who launched the Space Shuttle Challenger below design temps for the solid rocket booster O rings suddenly realized this as it exploded because of a leaking O ring.

Dave