L39 Backhoe problems

[korydz]

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 21/2 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.

 

[J_J]

You said: -Pressure showed it was good at idle and increased with throttle. It did not trip the relief.

You are supposed to trip the relief to check the pressure.

What were you doing to check the pressure?

On a good pump, you should not have much difference in pressure from low engine speed to high engine speed.

Every pump circuit should have a relief valve.

You can check the return pressure , and it should probably be less than 100 psi.

You mentioned main relief, is there a relief valve on the BH, and if so, what pressure did it relieve?

Is the main attachment pump supplying flow to both the FEL and the BH?

So, what you are saying is that when using the bucket or dipper, you get no or very little power even though the relief pressure is being met?

Which relief valve are you hearing?

If the FEL has a relief valve and the BH has a relief valve, install the gauge in the FEL IN port in a tee and use it to troubleshot the hyd system.

Max out one of the FEL cyl and note the pressure.

Then max out the bucket on the BH and note the pressure.

I would guess the BH problem is the BH pressure is set much lower.

Your BH cyl are much larger than the FEL cyl, and should develop much more power.

Let us know the pressure from each relief valve.

Recommend you set the FEL and the BH relief the same.

If you know how, set all the reliefs the same, including the 3pt.

When you check the reliefs, check upstream first, as that relief sets the max pressure. Check the relief is this order. FEL, remote , BH, 3pt.

You also have work port reliefs.

Relief #60 is swing relief

 

[kennyd]

I believe there is a relief valve on the BH valve itself, and it sounds like your testing the main one on the tractor side is that correct? Does your WSM cover the BH valve bank in detail and offer any testing for it specifically?

 

[ddbackhoe]

-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.

Does that procedure have you pressure test at each cylinder? I would check the pressure on the boom and dipper cylinders. There should be some pov's, check valves and pressure reliefs built-in to the spools. A little bit of junk in a spool can cause a lot of heartache too (doubtful if no ones ever pulled the thing apart)

 

[J_J]

korydz ,

We need some answers to our questions before we can help you more.

You have at least two relief valves on the rear of the tractor, and several of the valve stacks have work port reliefs, which are probably set reliefs.

It is doubtful that two pump would be that weak or bad.

You actually have two pumps.

The one pump has two sections.

One section is probably for swing, and the other is probably for attachments.

So if you set the FEL relief, that would probably set the relief for the BH.

So, do this to check this out.

Install the gauge in the pump line going to the FEL.

So in theory, if you maxed out a FEL cyl. you would see attachment relief psi setting.

Then max out a BH cyl, and you should see similar pressure on the attachment relief setting.

If you want to check the swing circuit, install the gauge in the swing pump circuit before any valve.

Then max out a swing cyl and observe the relief psi.

Let us know what you find out.

 

[Egon]

Are all the controls and valves on the tractor in the proper position. ie; fully closed or fully open. Engaged or not engaged?

 

[J_J]

There are also two relief valves on the loader control.

 

[korydz]

Thanks guys for all the responses. Great input. I guess I didn't do a proper pressure test on the main relief valve. When I go 2500 at idle and then it increased when I nudged the throttle, I figured that the problem was likely somewhere else. I'll re do it and see what I get.

When I'm operating the hoe, I can "feel" that it is relieving, but there isn't the whine that I would expect for a relieving valve. Are the relief valves on this machine particularly quiet? I didn't really consider testing all of the individual valves since the issue is common to all the circuits. I just have basic pressure gauge and the fittings to connect it to the backhoe ports on the L39 and the loader ports on my BX2660. If I need to start testing all of these circuits, I'll have to buy or borrow a more complete set up.

I'll try to find some time tomorrow evening to have another look at it and I'll keep you posted.

 

[ddbackhoe]

Thanks guys for all the responses. Great input. I guess I didn't do a proper pressure test on the main relief valve.

I'd say the main is close enough to not worry about. Sounds like you may need some more fittings, but I can't think of any other way around it. Common to all, boom, dipper (stick), bucket and outriggers (stabilizers)? Sounded like the outriggers were ok and you were down to 2 or 3 spools to check.

 

[J_J]

Would you not say that if he can not fully extend the outriggers that something is not right.

Anytime you can not extend a cyl, something is not working right or the design is wrong.