L 39 Backhoe problems

korydz

New member

Equipment
BX2660
Feb 17, 2009
17
0
0
Canada
I’ve got a problem and I’m looking for some help. The issue is very weak backhoe on my Kubota L39 TLB. 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.
 

North Idaho Wolfman

Moderator
Staff member
Lifetime Member

Equipment
L3450DT-GST, Woods FEL, B7100 HSD, FEL, 60" SB, 743 Bobcat with V2203, and more
Jun 9, 2013
30,552
6,600
113
Sandpoint, ID
I’ve got a problem and I’m looking for some help. The issue is very weak backhoe on my Kubota L39 TLB. 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.
First thing I would do is pull the 2, yes 2, relief valves and check both of them.
Next check the pump suction line for any damage or possibility of leaking and sucking in air.
Then at last, I think your going to have to get into the valve and check for any issues in it.
 

korydz

New member

Equipment
BX2660
Feb 17, 2009
17
0
0
Canada
Thanks Wolfman. I was digging into the manuals a little more this evening and discovered the second relief valve. I'll get on that next.
 

2grit

New member

Equipment
L35,U45
Apr 24, 2011
51
0
0
northeast
Make 100% sure before you do anything that the hydraulic quick disconnects that feed the backhoe are solidly connected and engaged
 

korydz

New member

Equipment
BX2660
Feb 17, 2009
17
0
0
Canada
Update:
I had some time to play with it tonight. No solutions yet, but checked a few things and I have a better description of the problem:

-I cleaned and reconnected the three fittings on the hoe.
-I pulled the boom and dipper relief valves out. They look clean and are not stuck.
-I did a pressure test on the main backhoe supply line as described in the WSM. 2500psi at idle and it climbed to 2700psi at full tractor RPM (2700RPM) and did not trip the main relief. I didn’t want to over rev the engine, but I think it’s safe to say this isn’t the issue. Diverter from BH to 3PT work properly.

I tried the hoe again and made some better observations:
-Stabilizers are fine.
-Bucket is fine.
-Dipper retract will audibly activate its individual relief valve when over pressured as you’d expect.
-Boom (both directions) and dipper extend fail.

Here’s the detail on what I mean by fail, and I should have been more clear on this before. If I try to lift the tractor with the boom (with the dipper and bucket tucked in), the cylinder will move a couple inches and then fail. It doesn’t just stop as it would if there was an over pressure relief, it actually drops any of the weight it picked up. There’s no sound of a relief, just the change in sound from the tractor from being loaded to unloaded.
More confusion: I was able to get the boom to fully lift the tractor a few times. It seems if I kinda snuck up on it by building pressure slowly, it would “catch” and then give me full power. I wasn’t able to replicate this on the dipper.

Do I just have a bunch of gunk in the spools? Is there any big trick to taking them apart and reassembling? Do I need new seals or o-rings or anything? Can I just flush the backhoe’s hydraulic system somehow? Keep in mind this is a 400 hour tractor in very good condition. It sat for perhaps as long as a year at the dealership. Everything I’ve looked at seems like it hasn’t been touched. No wrench marks or missing fasteners etc., so I’m tending towards issues from sitting rather than abuse or someone monkeying around with it.
 

MagKarl

New member

Equipment
L245DT
Aug 2, 2010
663
0
0
Olympia, WA
I would suspect a valve problem at this point since the weak behavior is definitely isolated to certain functions. I would pull it apart if it were mine.
 

Tarmy

Well-known member
Lifetime Member

Equipment
L2800, BH76A, FEL,box scraper
Nov 17, 2009
482
408
63
Lake Almanor, Ca
You got crap in a valve. I have had the same symptoms ...and issues. When I originally got my BH I had a paint chip from the manufacturing process in a valve. I was able to get it out and bingo.

5 years later I got something in one of the valves...and it has now finally moved down the block to the last valve...I am hoping it will work its way out in the next couple days...right now my side to side valve works...but won't hold its position...which indicates that it is caught in the seat of one side of the block or the other.

Either remove the valve and clean...really look it over and clean it spectacularly well...carefully. Or work it out.

Good luck...I hate these types of problems.
 

korydz

New member

Equipment
BX2660
Feb 17, 2009
17
0
0
Canada
Thanks for all the help guys. I think it's clear that I have some guck (technical term) in the valves or spools. I have a good friend that is a spectacular HD mechanic that works just down the road that has agreed to tear in to it for me. His tools and experience will all but guarantee results.

I know many of you would encourage me to tackle it myself, and if I had more time and less resources (like the above mentioned conveniently located professional) I'd be inclined to. The feeling of dread of losing a tiny spring or clip buried in one of these assemblies and not even having the experience to realize that I had done so is less than appealing.

Thanks again. I'll let you know how it all turns out.