Kubota BH77 Boom drooping

sherwood00 · May 5, 2017

Boom cylinder is drooping on my Kubota BH77 backhoe on a 2008 Kubota L3400 HST with 600 hours. There is no fluid leaking anywhere. I put one of those blue pills in the hydraulic reserve, but it still droops overnight. Haha...
When digging after it warms up it 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. If I turn the unit off and don't latch the backhoe the boom cylinder slowly droops down. The dipper and bucket cylinders appear to work fine and they don't droop when left extended.
I Took the rig to the Kubota dealer and they recommend replacing the Control Value and Pressure Check Value for $2360!? What the...! I'm instead 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?

wdchyd · May 5, 2017

Changing orings /seals in a control valve won't keep it from drifting if the spools and housing is worn. When the cylinder droops is the cylinder rod extending slowly?, if so you may have a piston seal by-passing in that cylinder.

sherwood00 · May 5, 2017

wdchyd said:
Changing orings /seals in a control valve won't keep it from drifting if the spools and housing is worn. When the cylinder droops is the cylinder rod extending slowly?, if so you may have a piston seal by-passing in that cylinder.

When the tractor is shut off the boom drops in about 2-3 minutes. That seems pretty fast? Dealer is charging me for the diagnostics they did before I said no to the quoted work. They hooked up a pressure tester to the boom cylinder lines and they say the lines were getting pressure and then it was fluctuating.

wdchyd · May 5, 2017

wdchyd said:
........... When the boom droops is the cylinder rod extending slowly?.........................

.....

sherwood00 · May 17, 2017

Solved: 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.

mguitas · May 17, 2017

Why don't you just rest the bucket on the ground, the you won't have to worry about the boom dropping. You should also have a boom lock too.

sherwood00 · May 18, 2017

I agree @mguitas. The real issue is when digging after it warmed up it would work for a while and then wouldn't lift the arm and bucket up. I had to wait a couple of seconds and then pull back on both levers to get it up. That problem has been resolved.