I’ve got a problem and I’m looking for some help. The issue is very weak backhoe on my Kubota L39 TLB. I know this is a little small for this forum, but I have a Deere 310C as well for credibility. 
I bought the tractor recently second hand from a non-Kubota dealer with 400 hours on it. It was a trade in from a known customer with no reported issues. It did sit on the lot for some time (a year?) so there could be some problems related to that. I’ve put 10 hours on it plowing snow and moving things around with the forks. I haven’t yet performed the 400 hour service and the associated fluid changes, but none of the fluids appear to be in any condition other than you would expect.
The loader and all other functions work flawlessly. The backhoe performs all functions quickly and smoothly, but with no power. It very much seems that it is triggering a relief valve almost immediately upon being loaded. The outriggers will pick up the machine easily, but the hoe won’t even budge it. I can hardly get it to pull through a snow pile with any of the controls including swing.
I understand that there are 3 pumps on the L39; main, swing and steering. I have a full set of manuals and have read up on any of the sections that appear to be related. I’ve searched the web and these forums without any luck so far.
Here’s what I’ve done so far without success:
-Topped up hydraulic fluid (it was over a gallon low)
-Performed pressure test as described in WSM 8-S15.
-Pressure showed it was good at idle and increased with throttle. It did not trip the relief.
-Quadruple checked that the flow diverters that switch from 3PT to backhoe were fully engaged (this is verified by the pressure test).
-I removed the main relief valve. It’s clean and operable.
-Reassembled and tested again. Still no power.
As soon as pressure starts to build, it bypasses or relieves somewhere. Here’s the crazy part. This machine has a separate swing pump and feed circuit to the hoe, and it does the same thing too. If the main pump was the issue, the loader wouldn’t be working properly (right?). The loader easily lifts the machine at idle and picks up whatever it seems it should, although I haven’t pushed it really hard yet as everything around here is still a frozen mess.
Where do I go from here? Replace the relief valve even though it tests and appears fine? Is there something gummed up or plugged? I can’t get my head around what it is other than the main relief valve. Even at that, the swing should still work since it has its own pump and feed line to the hoe. It only shares the return line. Is the problem in the return? Should I/can I do a pressure test on the return side of the circuit?
I have a great dealer that I bought one of my other tractors from, but he’s a 2 ½ hour trip away and I need to beg/borrow/steal a truck and trailer big enough to haul it. Even then, what are they going to be able to do that I haven’t tried yet.
I don’t have flow meter, but could get my hands on one if need be. I have all the speed and smoothness the hoe should have, just no pressure. I was blown away when the pressure test worked and now I’m at a loss. I know there are some sharp and experienced people out there. Any help would be appreciated.
I bought the tractor recently second hand from a non-Kubota dealer with 400 hours on it. It was a trade in from a known customer with no reported issues. It did sit on the lot for some time (a year?) so there could be some problems related to that. I’ve put 10 hours on it plowing snow and moving things around with the forks. I haven’t yet performed the 400 hour service and the associated fluid changes, but none of the fluids appear to be in any condition other than you would expect.
The loader and all other functions work flawlessly. The backhoe performs all functions quickly and smoothly, but with no power. It very much seems that it is triggering a relief valve almost immediately upon being loaded. The outriggers will pick up the machine easily, but the hoe won’t even budge it. I can hardly get it to pull through a snow pile with any of the controls including swing.
I understand that there are 3 pumps on the L39; main, swing and steering. I have a full set of manuals and have read up on any of the sections that appear to be related. I’ve searched the web and these forums without any luck so far.
Here’s what I’ve done so far without success:
-Topped up hydraulic fluid (it was over a gallon low)
-Performed pressure test as described in WSM 8-S15.
-Pressure showed it was good at idle and increased with throttle. It did not trip the relief.
-Quadruple checked that the flow diverters that switch from 3PT to backhoe were fully engaged (this is verified by the pressure test).
-I removed the main relief valve. It’s clean and operable.
-Reassembled and tested again. Still no power.
As soon as pressure starts to build, it bypasses or relieves somewhere. Here’s the crazy part. This machine has a separate swing pump and feed circuit to the hoe, and it does the same thing too. If the main pump was the issue, the loader wouldn’t be working properly (right?). The loader easily lifts the machine at idle and picks up whatever it seems it should, although I haven’t pushed it really hard yet as everything around here is still a frozen mess.
Where do I go from here? Replace the relief valve even though it tests and appears fine? Is there something gummed up or plugged? I can’t get my head around what it is other than the main relief valve. Even at that, the swing should still work since it has its own pump and feed line to the hoe. It only shares the return line. Is the problem in the return? Should I/can I do a pressure test on the return side of the circuit?
I have a great dealer that I bought one of my other tractors from, but he’s a 2 ½ hour trip away and I need to beg/borrow/steal a truck and trailer big enough to haul it. Even then, what are they going to be able to do that I haven’t tried yet.
I don’t have flow meter, but could get my hands on one if need be. I have all the speed and smoothness the hoe should have, just no pressure. I was blown away when the pressure test worked and now I’m at a loss. I know there are some sharp and experienced people out there. Any help would be appreciated.
