L39 Backhoe problems

[korydz]

I've posted this in "Hydraulics" as well hoping to find some help.

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. Itç—´ 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稚 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 2½ 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.

 

[beckmurph]

Don't know if this will help, but check Stonehallers comments in this thread:
http://www.tractorbynet.com/forums/...backhoe-swing-issues.html?highlight=L45+swing

 

[Stonehaller]

The main relief is shared with the loader and since the loader has power it most likely is not the main relief. It could be the tank line is restricted. Are you sure the quick disconnect is fully seated? If the return line was restricted, then the pumps would be loaded when the diverter valve is switched to the backhoe position. If you switch the diverter valves back and forth, do you notice a difference in load on the engine? There should be no difference.

If not the return line, then the swing cylinders, boom cylinder and dipper cylinder all have port relief valves. These are all set higher than the main relief and swing pump relief. The swing port relief is 2700 to 2770 psi. The boom and dipper are 3410 to 3480 psi. If someone backed off the adjustment on all those, then you would lose power on those circuits. The stabilizers and bucket cylinder do not have port relief valves. That may be a clue since you state the stabilizers can lift the tractor.

 

[dbutler]

I have an L45 with an intermittent problem with the boom cylinder. It fails to pull back once in a while, then it will start working just fine. It also drifts down if it has a load, such as a log in the bucket/thumb. My dealer said each valve has a relief valve attached to it. They are visible on the valve body below the backhoe control levers. He said this very likley to be my problem. Im not going to try and take the relief valve apart myself so it will go to the dealer soon for repair.

The machine has about 500 hrs and all fluid and filters are up to par. All other function of the tractor and backhoe work fine. Keep us posted what you find out.

 

[korydz]

Thanks for the input and responses. There is no change in the engine load when the diverter valves are actuated. I keep thinking it has to be something common to all of these circuits since all function are being effected. The bucket has the same weakness as the boom and dipper. I'll have a look at the individual relief valves, but it seems unlikely that they all would have a common and consistent issue. I did stumble upon a second main relief valve in the WSM, so I'll check that one out too. I'll keep you posted.

 

[mike69440]

There is a lever on the back of the hoe that can get disturbed when removing the hoe. It's down where the 3 pt is. Only time i ever had to mess with it was when dealer took off my hoe after an elecrical fire.

I never take my hoe off, so I don't remember exactly wher the lever is or if it has to be completely in or out. Search the forum (It was described in an M59 thread i think??)

 

[Stonehaller]

Make sure the auto level function on the loader bucket is turned off.

 

[korydz]

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 軋tch 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.

 

[powerstroke444e]

Make sure the thumb valve is not stuck. And that the 3point level is not and dead heading. It really seems like you have a return line that is not hooked up.

 

[Stonehaller]

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.

If you plugged a gauge into the main backhoe supply port as shown in the work shop manual, then you are dead heading the pump and dumping all oil flow over the main relief.

Dipper retract will audibly activate its individual relief valve when over pressured as you'd expect.

Just running the dipper cylinder to the end of travel in either direction or stalling it against the ground should activate the main relief not the work port reliefs on the dipper valve. The work port reliefs should be set higher than the main relief. The work port reliefs protect components from inertia loading and from over powering with external force such as the bucket.

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 軋tch and then give me full power. I wasn't able to replicate this on the dipper.

Either the work port reliefs are set too low or the piston seals are leak in the cylinder. To check the piston, run the cylinder to the end, take the return hose off and try extending the cylinder. If you get oil flowing out of the return port, then the piston seals are leaking.

The work port reliefs also have anti-cavitation checks. It is possible there is debris in them preventing them from fully closing when pressure is applied. You said you took the work port reliefs out, but did you disassemble them for inspection?

Have you checked a sample of oil to see if it is contaminated with water (milky) or aerated (full of bubbles)?