B2710 with LA 401 FEL won't go up!

[Girtski]

Posted this in the Kubota Owning/Operating forum and thought I might get more help here.

I have a B2710HST with an LA401 loader with 4 position valve. Never has my loader bucket raised consistently to the prescribed height. Occasionally it would, but mostly it only went up about 3 feet until recently. It now only raises about 10". I changed the transmission fluid from Super UDT to Super UDT2, changed the spin-on hydraulic filter, cleaned both screens (which were not at all dirty). I had both of the lift cylinders independently tested by a hydraulic shop and they tested good. None of this made any difference in the height. It sounds and feels like it's reached it's limit when I raise the bucket.

If I take the hoses off and put them on the curl/dump side, the bucket raises full travel and lowers fine. I replaced both detents with new kits a couple years ago because they were sticky and rusted. That made no difference at the time.

I've read where the quick-couplers could cause problems so I swapped them from side to side to see if that would make any difference. It did not.

What I did discover when taking out the quick couplers was that the top port in which the coupler screws on the lift side has no holes in it. It's a dead port. I'm wondering if this is normal? If so that would only leave one port for raising and lowering. Since there is no hole for oil travel I suspect this to be normal or the bucket wouldn't work at all. I would love to see a hydraulic schematic showing the fluid flow during lift and drop activity.

Can anybody give me some tips on things to try next? Although not a hydraulic specialist by any means, I am a mechanic by trade and do not understand why I have intermittent operation and now am only limited to 10" of lift.:confused2:

 

[J_J]

It sounds like you may have a restriction in a hose or fitting.

Remove the hoses at the tee to the lift cyl, and place in a clean bucket.

Activate the lever in fwd and rev, You should get fluid flow in both lever movements.

If you can't get fluid to the cyl's, they are not going to lift. That little bit of lift may be some leakage past the blockage.

A hyd gage in the lift hose fitting should give you pressure and you should hear the relief going off.

 

[Girtski]

It sounds like you may hav arestriction in a hose or fitting.

Remove the hoses at the tee to the lift cyl, and place in a clean bucket.

Activate the lever in fwd and rev, You should get fluid flow in both lever movements.

If you can't get fluid to the cyl's, they are not going to lift. That little bit of lift may be some leakage past the blockage.

A hyd gage in the lift hose fitting should give you pressure and you should hear the relief going off.

Thank you JJ for your reply.

I will try that verbatim but I have to get the detent put back together first...Fighting with the 4 small balls, spring and one large one. Diagram is not crystal clear on sequence and since it came apart in rusty dirty pieces and it's been a few years since I last did this repair, I can't remember how I reassembled.

Since I am getting a full stroke when I switch the quick couplers to the curl/dump side, wouldn't I be better off taking the pressure reading at the valve?

Should the valve body be drilled on the top port or is both up and down controlled by the one port?

 

[J_J]

You can install the hyd gage at the IN port with a tee and it will indicate pressure, or if there are QD's, just plug the gage into the QD and engage the lever for a moment.

If the fluid was being blocked, you should have heard the relief going off.

 

[Girtski]

Still plan on putting gauges on this when I get it back together however Kubota technical assistance finally got back with my local dealer on the question about the port not being drilled. Apparently there were some valve bodies which missed a machining operation. I still can't understand why it would work from time to time or why it would consistently raise about 3 feet since I owned it. Dealer is supposed to drill the port today. I will make every effort to ensure metal shavings are cleaned out and reassemble this weekend...stay tuned!

 

[J_J]

I just can't believe the valve does not having two work ports for lift, and two more for the curl. . They must have tested it when installed.

If any one of the work ports were blocked, the relief would be screaming.

Which work port has no fluid coming out of it?

What pressure did you read on each work port?

You should ask the service manager to show you the service bulletin on the drilling out thingy.

Do you have any pictures of the plugged work port?

 

[hayden]

Can you curl a decent weight? And can the 3PH lift something heavy? If so, then you are developing pressure and your relief valves aren't releasing prematurely. That would eliminate the reliefs as the problem.

It sounds to me like a bad spool in the loader valve, and this un-drilled port sure sounds odd.

The circuit is very simple. Two hoses, one to power up, the other to power down. The two cylinders are coupled via piping on loader frame. When you move the lever to lift the loader, the lift side gets pressurized and the other side goes to the tank. Lowered or applying down pressure does the same thing, but the ports are reversed. In float, both lines go to the tank.

JJ's suggestion of disconnecting the hoses and running them into a container will let you see if you have equal fluid flow from both ports.

 

[Girtski]

JJ. There is no technical service bulletin on this issue. According to my dealer support guy, Jim from Kubota told them to drill a hole..apparently anywhere in the port. I suspected this might be an issue since inside the valve body are several "dividers" I got the valve body back from the dealer today. They drilled a hole in the port and as I suspected, left a burr in the bore where the spool goes. Also it turns out the hole was drilled right in the middle of one of the "dividers". After removing the burr, I inserted the spool and had to "tap" it in where before it would slide in with little effort. I expected to have problems and I do. Right now the spool is too tight and will not return to "neutral" position with the spring pressure. I have to manually center it. The lift seems to work really slow but it does go all the way up. I am going to fashion a note to kubota asking for an explanation and advice for resolution....
Here are a few pics...

 

[J_J]

Nice pictures. They should have cleaned it out more and smoothed the edges. You might also run a small magnet in the bore and see if you pick up any more bits of metal.

Is that hole too deep for a Dremal tool and a small ball grinder, or a curved file?

 

[Girtski]

Nice pictures. They should have cleaned it out more and smoothed the edges. You might also run a small magnet in the bore and see if you pick up any more bits of metal.

Is that hole too deep for a Dremal tool and a small ball grinder, or a curved file?

I did run a magnet through it and did not pickup anything until after I filed off the burr. The hole is a bit on the small side but likely not too small for a dremel stone. However I've already reassembled the unit which brought me to the conclusion of the bore being distorted enough to restrict the smooth operation and return of the spool to neutral when I let go of the lever. Ironically I finally received a response from Kubota technical assistance on the issue of whether or not there were any TSB's on the valve. They didn't answer my question, only suggested that I take it to my dealer. After seeing them prick punch the bottom of the bore thinking that it was a stuck check valve rather than the lack of a hole in the port, I don't think much of the dealerships' understanding of how the system works. Not that I understand completely. In my response to Kubota, I further explained the symptoms and the subsequent suggestion of their tech person to "drill a hole" in the port. Also the tech person was quoted as saying "every so often a valve may be missing a hole".

While I do believe the hole was needed, I don't believe it was done in the correct location now that it's reassembled and I have to utilize the lift/curl motion of the control stick to get it to raise with any speed. If I only use the lift motion it goes up all the way but it takes about a minute to go from the ground to 6' height. Stay tuned...this one's not over...