Back hoe Boom issue

[otter]

While digging footing holes today my BH77 on a L3800 HST the boom lifting function started working intermittently. 261 hours and UDT and filter replaced last spring.
Fluid levels all good.
Power to dig in down mode.
All other hydrolic functions work well.
Moved the lowering adjustment knob in and out. This seemed to allow the boom to lift if adjusted out. Then the boom would not work so I would screw the adjustment in and the boom would work again for a limited time.
Link arm in the down position.
Sometimes changing the rpm would allow limited and temporary use of the boom.
Hoses were removed and reattached.
Hydrolic relief valve removed, looked over and replaced.
Safety valve removed, looked over and replaced.
When the tractor was new to me, the lowering adjustment knob was 'Frozen' until I was able to get it free.
No issues last year with any hydrolic functions prior to winterizing for 6 months.

Anyone have a suggestion of where to check for the bad link?
No flow meter or pressure gage.

Thankyou

 

[Tarmy]

I have the BH 76... And have had similar problems two times over the years.

Both times I tried what you did to isolate the issue...both times it turned out to be crud...small flecks actually, stuck in the control valve assembly. One time was a paint chip...the other a very small metal chip that got loose somewhere after the filter and lodged in the valve...then eventually moved to another valve...then worked its way out...took a month...pain in the ass.

Choices include trying to clean out control valve...or if it moved to the actual cylinder...there are threads on how to check the cylinders...

 

[otter]

Thank you for the response tarmstrong.
There must have been a bit of grid in the valve as the malfunction did not account during use today. Hope the contaminated in the filter and I am done with it. It is a pain

 

[otter]

Cyceling this thread back with more information regarding the issue.
After have intermittent issues with the back hoe boom lift, but in general its worked well until this spring/early summer, when the lift simply would not respond.
Started by removing the upper relief valve for the boom (#6 on WSM page 1-M2) for disassembly, cleaning and reinstalling. Did not help the lift issue.
I switched #6 and #7 (boom swing) upper relief valves, tested and no soluion to the boom lift.
Next I switched the #6 and #7 relief valves on the bottom of the valve assembly.
Bingo! The boom lift worked well and no noticeable change in the boom swing.
Still do not know what the issue was/is but the solution worked for digging eight post holes.
Switching hydraulic lines between functions (for testing) was a no go for my XXXL sized hands anoungst the lines of the valve hook-ups.