BH77 boom cylinder droops

[sherwood00]

The boom cylinder is drooping on my BH77 which is on a 2008 L3400 HST with 600 hours. There is no fluid leaking anywhere. I put a blue Viagra pill in the hydraulic reserve, but it still droops overnight. Haha... anyways, when digging and the tractor is warmed up it suddenly won't lift the arm and bucket up. I have to wait a couple of seconds and then pull back on both levers to get it up. The dipper and bucket cylinders appear to work fine. When parked the boom droops unless the safety latch is set.
I Took the rig to the Kubota dealer and they recommend replacing the Control Value and Pressure Check Value for $2360!? What the...$$! They're charging me $400 just for doing diagnostics on the boom cylinder line to determine that the pressure was indeed fluctuating. I'm bringing the rig home and plan to take the control value and pressure relief value apart, clean it, reassemble and hope that in the process I find a bad o-ring or some obvious reason for the leakage.
Anyone have advice about this drooping issue beyond buying the backhoe flowers and dinner or has anyone done a control value rebuild? I've seen the job referred to in threads but no details.

 

[Tarmy]

My BH droops overnite too...same year...I have always gotton in the habit of relieving pressure when done for the day. I don't worry about it...no leaks...just leak down. By relieving the pressure by setting down the arm and front bucket...I don't worry about someone touching anything and dropping one of the implements on themselves or a foot or a cat or something...

 

[sherwood00]

It happens, right? But, this issue happens when I'm trying to dig and the boom droops and I have to wait to get 'pressure' back in order to keep digging. Just the Boom cylinder is effected. That's why I need feedback on rebuilding the Control Value block where the Boom lines come in to the unit.

 

[lugbolt]

2" per hour leakdown rate is acceptable by Kubota's standards, or that's what I was told anyway. This with the dipper fully crowded, and measured at the rearmost part of the bucket.

I though 2" per hour was excessive but that's what they told us.

 

[Tarmy]

On occassion I have the same dropping while operating problem. I figured out that a speck of contaminant like a paint chip or metal shaving can work its way through the hydraulic system. They lodge in the valves...and sometimes they work their way through.

I have had it happen three times...this last time, which is still occuring as OP describes, it has not cleared. I got to them same point where I shopped for a new valve block and found out that the part is 2500... I am about an inch away from actually buying a new one and installing it.

I figure that I can have a spare one that I will swap out if it keeps happening...which it does.

OP, if you do get a new valve block set...post the results and time it took to install...my guess was...all damn day for mine...

 

[sherwood00]

We're into the project and I can see why it has an estimated 8-9 hours of labor. Thought we'd do a quick swap of the hydraulics for the swing and the boom and that would allow me to test the boom cylinder while the swing was then problematic. The blocks are next to each other on the Control Valve housing. They are #1 (swing) and #2 (boom) from the right looking forward. But, the swing has a 90* fitting and those wont go in the boom block w/o removing the fittings in the #3 block and you get the picture... Need a straight fitting to do the test swap and it's a Sunday. Gonna end up taking the whole thing apart, I can tell.

 

[sherwood00]

We swapped the hydraulic lines for the boom and swing cylinders and the problem moved to the swing cylinder so I have no doubt that something inside the boom control valve block is allowing pressure to slide by.
We've got two hours into the project and a greater appreciation of what a PITA it is to work on the control valve! See the pic of the mess of lines in the tight space!
The next step is figure out if there are any short cuts to get at the spool and check valve in the block. Hopefully this can be done with out removing anymore hydraulic lines from the other blocks. Probably need to order a Workshop manual for the BH77 unless someone can send me the page that shows how the spool is accessed.
I'm hopeful that we can remove the four bolts that hold the entire control valve to the hoe and then I'll have the space to remove the bottom relief valve [7K502-63710] and access the spool [7K502-63550] and then pull out the check valve and top relief valve and give it all a cleaning.

 

[otter]

Following your post.
My BH77 is having the same issue and getting more pronounced.

 

[Sammy3700]

Mine is also. Gone try what lugbolt posted next time I have it on.

 

[Tarmy]

Any update or progress?

 

[sherwood00]

Success! Or so it seems. I haven't had a chance to a lot of digging to be 100% sure but it seems like we got it figured out cuz the boom doesn't suddenly drop or fail to respond while under load. The best part is that we found a problem that I can point at and say - yup, that was it! Very satisfying. Very unsatisfying that the dealer's mechanic handled the same part and didn't catch it or failed to mention it in his notes. When I snorted at the $2500+ estimate and said stop work the bad part was put back in the unit.
Enuf blah, blah, here's the sequence: We pulled the check valve out of the boom block and inspected that bc I had heard someone found crap in that. Compared it to the check valve for the swing block and it was clean. Pulled the top and bottom pressure relief valves from the boom block [7K502-63710] and compared them. They were actually easy to get to and remove. BINGO! Tears of freak'n joy! The bottom valve had a little button sticking out of the end that goes into the block like the clicker on a pen. The top one didn't! Pulled the top pressure relief valve from the swing block and it also had a button on a spring. More tears of joy! Took the buttonless valve apart on the vice and removed the plunger, cleaned it and reassembled but could not get that button to stick out. Will price a new part - have to buy the whole thing, [7K502-63710]. Put the bad pressure relief valve on the top of the swing block and the one from the swing block on the boom block. Put everything back together and went digging. All worked as advertised. More tears of joy. Even had a man hug with the neighbor cuz I bought it from him and paid top dollar for the unit. Didn't want bad blood cuz of $$$. I'll post some pics next.

 

[sherwood00]

File names sort of tell what you're looking at. The pic of the high pressure relief valves on top of the unit shows that the one on top of the boom block had recently been handled and cleaned off. That must of been pulled by the dealer mechanic when they did the pressure test in the boom block. Too bad he didn't notice the plunger wasn't presenting like a little button on top or that his notes never made it to the invoice for $400 I had to pay for diagnosis.

 

[otter]

Thanks for posting the results!!

 

[Tarmy]

OP...So help me understand what you found...

I read your posts a couple of times...and if I understood your write up...you had a bad pressure relief valve...and just swapped around good for bad to test your theory?

Thanks...

 

[sherwood00]

First we swapped the hydraulic lines where they go into the control unit: boom for swing and that seemed to transfer the problem to the swing. That showed the problem was in the block where the boom cylinder lines connect to the control unit and not a problem with the boom cylinder. Put the lines back where they should be and then swapped the pressure relief valve on top of the boom block for the one on top of the swing block and the boom appears to be working alright. The bad pressure relief valve (the button on the pressure relief valve is stuck) that is now on the top of the swing block may be effecting the operation of the left-right swing cylinder but I'm not noticing it yet. The boom is no longer drooping DURING operation. It still droops overnight. Maybe I haven't found the real source of the problem but so far it looks good. The pressure relief valve costs $315+ online.

 

[Sammy3700]

Thanks for the information.

 

[Tarmy]

Thanks OP...

Welcome to the forum! This place is great for things like you just experienced...lots of help in here...sometimes you get to do the helping!

 

[kennyroy]

Mine was the pressure relief valve! exspensive! (b26)

 

[Henro]

Mine was the pressure relief valve! exspensive! (b26)

Good for you, but I HATE reading 5 year old (or more} threads thinking they are current issues!

I wish there was some notice posted to show an old thread was resurrected. Not saying resurrecting an old thread is a bad thing...plenty of very meaningful old threads...

But just to say "me too" ?

Edit: Yes I know the date of the original thread is shown. My weakness is that I read the thread titles and never check dates, assuming they are current. IF the dates of old threads were highlighted in RED this would help old guys like me to comprehend things...

 

[lynnmor]

Maybe I should start a new thread, but I have the drooping problem as well and the previous information is pertinent to my question. I have the BH70 backhoe, the parts diagram shows the relief valves like the BH77, but with slightly different part numbers, I see no relief valves like that on mine. Maybe there was a change and the parts list is not up to date. I would think that there must be pressure relief, so does anyone know if relief valves are now embedded inside the valve block?