B7800 and a LA402 FEL problem and fix

[rjent]

I though I would pass this on to anyone who is interested. I have owned Kubota's for decades and have never been let down ... until now ... but it wasn't the tractors fault LOL

My FEL quit having down pressure. Everything else worked. Bucket tilted both ways just like normal, the boom would lift, although weak and wouldn't lift any weight.

I have a degree in Ag hydraulics (not just, but you get the idea ) so I took the valve off the machine and disassembled it to no avail. I was really stumped. I called a dealer in Albuquerque (Mesa Tractor) that I have done business with before and talked to a tech. Found out that if the 3 point lever is stuck in the up position, the FEL will have these symptoms. I had lent the tractor to a friend of mine and he was sick that he had "broken" it.

Anyway, long story short, it cured the problem, I am now "educated" so it won't happen again and after scouring the Interwebs for days and not finding anything, I thought I would share.

If your FEL is weak, check your 3 point control...

 

[GeoHorn]

Are you saying that if the position control lever is in the UP position, the FEL is weak? That makes little sense to me because that’s exactly how I operate much of the time and I’ve not had any FEL problems. (When I use my FEL ... my finish mower is usually hanging off the back with the position lever all the way UP.)

 

[chim]

I remember having an issue with something like this. A simple adjustment of the feedback rod solved it. I think that the hydraulics were bypassing fluid when the 3 point lever was all the way up.

 

[lugbolt]

not all kubota's have the same issue.

The B series doesn't have true position control, so when you just jerk the lever back and leave it (lever is supposed to return to neutral when 3ph all the way up), and it doesn't return to neutral like it's supposed to, you are taking all of the hydraulic power from everything else but power steering and applying it to the 3ph cylinder, at which point your FEL ain't gonna work right. If you know how to read a hydraulic diagram you'll see what I mean.

Most tractors place hydraulic precedence in this order: 1=hst. 2=power steering. 3=3 point hitch. 4=FEL.

Tractors that have true position control (L and M series come to mind) have a position control valve with feedback. On the L series there is an external rod on one of the rockshaft arms. That rod's adjustment is critical! If the 3ph is allowed to lift all the way to it's stop and then keep applying pressure, yeah the FEL, backhoe, or whatever else is on the power beyond circuit WILL suffer poor function, guaranteed.

Usually it's easy to tell when you're "out of adjustment". When you grab and pull the 3ph lift lever, when it's all the way up the 3ph will stop going up, but if something ain't right with either the lever or the feedback link, you'll hear the engine labor, as if it's loaded (and it is)...that is the hydraulic pump trying to move the 3ph up higher but it cant because the piston is bottomed out in it's bore. Continuing operation with it "dead headed" will result in fluid heating, loss of operation of one or more hydraulic components, and/or hydraulic pump failure, and occasionally a failed aka busted internal lift cylinder assembly. I have seen all of the above happen, several times. Listen to the engine and your system while operating if you can.

 

[rjent]

My B7800 has a backhoe with the PTO driven separate pump and oil reservoir. It maintains a certain position on the 3 point whether the 3 point lever is moved or not. The tech said that if the 3 point lever is in the full up position, it robs pressure and flow to the FEL, makes no sense to me either, but that is what it was. My friend apparently accidentally "elbowed" the lever back into the up position. Since the 3 point can't go up, the lever stays.

 

[GeoHorn]

not all kubota's have the same issue.

The B series doesn't have true position control, so when you just jerk the lever back and leave it (lever is supposed to return to neutral when 3ph all the way up), and it doesn't return to neutral like it's supposed to, you are taking all of the hydraulic power from everything else but power steering and applying it to the 3ph cylinder, at which point your FEL ain't gonna work right. If you know how to read a hydraulic diagram you'll see what I mean.

Most tractors place hydraulic precedence in this order: 1=hst. 2=power steering. 3=3 point hitch. 4=FEL.

Tractors that have true position control (L and M series come to mind) have a position control valve with feedback. On the L series there is an external rod on one of the rockshaft arms. That rod's adjustment is critical! If the 3ph is allowed to lift all the way to it's stop and then keep applying pressure, yeah the FEL, backhoe, or whatever else is on the power beyond circuit WILL suffer poor function, guaranteed.

Usually it's easy to tell when you're "out of adjustment". When you grab and pull the 3ph lift lever, when it's all the way up the 3ph will stop going up, but if something ain't right with either the lever or the feedback link, you'll hear the engine labor, as if it's loaded (and it is)...that is the hydraulic pump trying to move the 3ph up higher but it cant because the piston is bottomed out in it's bore. Continuing operation with it "dead headed" will result in fluid heating, loss of operation of one or more hydraulic components, and/or hydraulic pump failure, and occasionally a failed aka busted internal lift cylinder assembly. I have seen all of the above happen, several times. Listen to the engine and your system while operating if you can.

Lugbolt, THANK you for that! Makes perfect sense... NOW.

There are times that I’m reminded how a Forum is supposed to work and this is one of those times. Thanks to you Lugbolt and to NIW also for helping the rest of us.

 

[Henro]

My B7800 has a backhoe with the PTO driven separate pump and oil reservoir. It maintains a certain position on the 3 point whether the 3 point lever is moved or not. The tech said that if the 3 point lever is in the full up position, it robs pressure and flow to the FEL, makes no sense to me either, but that is what it was. My friend apparently accidentally "elbowed" the lever back into the up position. Since the 3 point can't go up, the lever stays.

I had a problem in the past with my B2910 (same tractor as the B7800) while my backhoe was on. I think it would not move properly and low power on hills as compared to normal.

Asked what might be wrong on (TBN I think), and someone said check the 3PH position lever.

The lever was in the UP position, as I forgot to put it back down after installing the backhoe and using it to position the lower links. As soon as I lowered the lever, the problem disappeared. I became a happy camper at that point (and a believer).