B2710 3 PH not raising

[jasonf]

Guys:
I am having a problem with my B2710:
Sunday I connected my KK bush hog to my 3 PH and lifted it off it's storage pallet. I moved it to the driveway and move the 3 PH position control valve from full up to full down, like a knucklehead. /forums/images/graemlins/shocked.gif The hog came crashing down onto the driveway, and then would not raise up after that. /forums/images/graemlins/frown.gif

I checked the loader and it works fine, and can lift the front wheels off the ground. It curls and dumps at the normal rate, but the 3PH won't lift up. When I try to lift the 3PH I can hear the hydraulics hissing as it tries to lift the brush hog. I removed the pins that connect the upper arms to the lower links, and am able to lift the arms from full down to the full up position using the position control. In fact I can hear the feedback control arm closing off the hydraulic flow as the arms approach the full up position. I lower the arms to the half way position, and then close the control knob in front of the seat to lock the arms in place. When they are locked in place I can put all my weight down on the arms and they will stay locked in place. With the position control lever still at the halfway mark, I return the control knob back to its normal unlocked position, then I can push the arms from the halfway position down to the down position. When I release my grip the arms return back to the halfway mark. I can feel the hydraulics fighting me as I press down on the arms, but it is like they don't have enough force to stop me. /forums/images/graemlins/confused.gif

Since I can lock them in place with the control knob, the piston seal must be OK in the 3PH. I suspect that the position control valve was damaged and is allowing some fluid to pass through to the sump, and only a portion of the flow is going to the 3 PH cylinder (feels like maybe 10% up force). I have removed and inspected the relief valve that is in the top of the 3PH case, and it appears to be fine.

I have power washed the top of the 3PH case and have removed the bolts holding it in place. I was about to remove the cover, but was being attacked by the mosquitoes, at dusk. /forums/images/graemlins/mad.gif My plan is to inspect the position control valve as the shop manual indicates, but was hoping that someone else had run into this problem, and could offer some advice.
Anything would be helpful at this point..... /forums/images/graemlins/confused.gif I posted this in the Kubota Owning, but did not get any help. Hope someone has a clue....

 

[Bird]

I think you have an unusual problem the rest of us have not had. Sorry I can't help with that one.

 

[Henro]

<font color="blue"> I suspect that the position control valve was damaged </font>

I doubt I can help find the solution, but I can tell you that on my B2910 I let the 3PH drop at full speed probably a hundred time or more, when carrying dirt in the dirt scoop. Maybe 200 hundred times even. And it never affected the position control or the lift capability of the 3PH.

Grabbing at straws, I would check all the external linkages and try to see if anything is slipping...something bent or loose, that sort of thing.

Hope you find the solution easily.

Another thing I would try is cycling the 3PH top to bottom a number of times...perhaps somehow you sucked some air into the system...

Just WAGS...worth nothing perhaps, but they don't cost much either... /forums/images/graemlins/grin.gif

 

[aloha]

This is from the Kubota operator's manual for B2710, B7800, B2910: "If the 3-point hitch can not be raised by setting the hydraulic control lever to the UP position after long term storage or when changing the transmission oil, turn steering wheel to the right and left several times to bleed air from the system."

It sounds unlikely to be the cure, but easy enough to be worth a shot.

 

[jasonf]

Well, I have taken the 3PH cover off, after removing the seat, and all the levers. I took it into the basement and flipped it up on its back to look at the position control valve. After removing the positioning valve I have 2 holes that the valve bolts over. One of them goes to the pipe that delivers fluid from the hydro pump, the second hole goes directly to the 3PH piston. When I apply compressed air to the piston hole the arms immediatly move to the full up position and stay there as long as I apply air, when I remove the air the arms go back down. So I know the piston and seal are OK, which is what I suspected. I have completly disassembled the valve and have not found any broken parts.

I have injected air into the ports on the position valve but it is not letting the air through into the port that feeds the 3PH lift cyl. According to the book when the valve is in the neutral position, the oil entering the valve passes right through and is dumped back into the sump through a weep hole that has a poppet valve at a right angle to the weep hole. When the spool is moved to the lift position, a small amount of the hydro pressure is fed to the back of the poppet valve, closing it. So instead of letting the hydro fluid pass back to the sump through the weep hole the fluid is now blocked by the poppet valve that has closed because of pressure behind it. The fluid is now forced to go out the position valve onto the 3PH lift Cyl. When I use air to test, the poppet valve, it is still letting the input air pass back to the sump, not toward the cyl. I have checked the poppet valve and it is clean and not stuck. I think using air is not going to work, I need to figure someway to pressurize hydro fluid and use it instead for testing since some of th hydro fluid is needed to open/close the poppet valves....

Any ideas on how to test using fluid? I think that I am going to have to reassemble the valve, bolt it back in place. Then take the top and set it over the sump with 2 2X4's spacing it off the top of the trans case so I can see what is passing back into the sump below, and also how the spool of the position valve is behaving. In this position, I should be able to hook the pipe from the hydro pump back up to the 3PH case top.

Any other ideas are sure welcome....

 

[jasonf]

Well I have reassembled the case cover with the control valve and the 3PH lifts from down to up, as long as the upper arms are not connected to the lower lift links. I tested it without a load on it, and thinking that it was working I reassembled the whole tractor. /forums/images/graemlins/blush.gif Of couse after it was completely assembled I attached the lower links and tried to lift the brush hog. It lifts all right however it then bounces up and down as soon as the brush hog is lifted completely off the ground. If I lift it VERY slowly I can get it to go up and stay at a certain position. However if I raise it normally, it bounces up and down about once a second, and it is so bad that the front wheels almost come off the ground /forums/images/graemlins/blush.gif If the 3PH is lifted all the way up it will hold the hog steady, but as soon as it comes down at all it starts to bounce. /forums/images/graemlins/mad.gif

Yes I have bled the loader, 3 PH and the steering, and have check the oil level. I think that there is a piece of crud in the valving that is causing this jerking motion. I tried to be careful when I scraped the gasket surfaces, but it is possible that something slipped by. The 2710 has a 'shockless' system that reduces jerks when you adjust the 3PH, and it has 2 TINY holes drilled into the hollow center of the spool. These holes are very small and may be blocked.

Any advice from the hydraulic mechanics out there would be appreciated (and any non mechanics also /forums/images/graemlins/grin.gif). I am going to be disassembling it this Friday, and will check on the condition of the poppets as well as the unloading valve. This time I will not reassemble the whole thing until I connect the 3 PH upper links to the lower and test it under the load of the brush hog. /forums/images/graemlins/crazy.gif

 

[jasonf]

OK, I have fixed it, and here is the story:
I took the control valve COMPLETELY apart and found a TINY piece of crud when I cleaned out all of the internal passages. I washed every part carefully, including the steel valve body itself. It seems that it only takes a very SMALL piece of crud to ruin you day /forums/images/graemlins/confused.gif However after assembling it carefully, it is now working properly, and all is well..... /forums/images/graemlins/grin.gif

 

[slowrev]

Jason,
Glad to hear it is working again. Thanks for the update. How do you think the crud got in there ? Quick connect hose end or something ?

Ben

 

[Mgray]

Jason,

I was glad to see this post. I am having what appears to be the exact same problem. I have a b2710 also. The symptoms you described match exactly what I am seeing. I called a local dealer and they said that it could be any number of things but it could be as much as $1100 (with pick-up and delivery) if a cylinder seal needed to be replaced. From what I could tell from the posts, it seems like removing the control valve and giving it a good cleaning is the fix for this problem. I am going to wait for the weather to warm up a little before I attempt to repair.

Based on this post I have the steps as, power wash the top of the tractor, remove the part, clean thouroughly, and replace.

I did have a few questions. Did you buy gaskets or did you cut your own? Did you use any sort of cleaning solution? I have an extensive mechanical background but none in hydraulics so this is a new area for me. Did I miss anything?

Thanks
Mark

 

[slowrev]

Hmm, I guess this is why my old IH has a high pressure side filter in the line before the fluid gets to the lift box.