Help with 3-point hitch repair

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

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.

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

North Idaho Wolfman said:

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.

Click to expand...

Thank you both; very helpful.

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

Re: Interim report on 3-point hydraulic refresh

wdlanning said:

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

Click to expand...

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.

Re: Interim report on 3-point hydraulic refresh

Mark15 said:

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.

Click to expand...

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.

Re: Interim report on 3-point hydraulic refresh

North Idaho Wolfman said:

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

Click to expand...

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

Re: Interim report on 3-point hydraulic refresh

Dave_eng said:

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

Click to expand...

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