I have a L45 TLB with a hydraulic thumb. The thumb moves end of stroke to end of stroke with the foot pedal. The problem I'm having is the thumb has little pressure for holding a rock or log. I loosened the top nut on the valve & turned the adjustment screw clockwise a 1/2 turn (holding the screw) & re-torqued the 17mm nut to 4-5.7 lb.ft. I tested the pressure by using a fairly large rock (I don't have a gauge) & it did nothing. I ended up doing this procedure until the screw was turned 2 full turns. The thumb seems to be holding the rock better, but not where it should be. I can actually retract the thumb with moderate arm force. Should I keep turning the screw (it's recessed quite a bit into the nut) or possibly remove screw & spring & install a thin shim(s)? I made sure not to damage the cylinder piston for the thumb. Love to have input from the experts. Thanks in advance. Joe
Hydraulic thumb adjustment
- Thread starter Backhoe Joe
- Start date
kubotafreak
Well-known member
Equipment
GRAND l6060, L3560, B6100, gr2100, tg 1860, g1800, g1900, g2160
Really should test the pressure. The cylinder or valve may be defective. The bucket curl should be slightly stronger than the thumb.
Thanks for the reply. I know I should test the pressure with a gauge. I'm sure I would get an extremely low reading. I'm not even in the ball park of around 2000 psi if I can manual lift the thumb. I know about the bucket curl as I stated. I have no leaks which doesn't matter in my situation. What is the best procedure to test the cylinder & valve? Thanks again.
You could have an internal leak in the cylinder. Really need to test pressure and go from there.
That makes a lot of sense about leaking internally. I'll test the dual action cylinder. If defective, I'll order a seal kit. Thank you.
kubotafreak
Well-known member
Equipment
GRAND l6060, L3560, B6100, gr2100, tg 1860, g1800, g1900, g2160
Chances are you have a bad relief valve. But as far as testing pressure I would suggest an inline t, so you can see it while working, not just dead heading.
Thanks, I'll take your advise once I test the cylinder. Do you know a way to test the relief valve? If the cylinder test good & the pressure gauge then drops, I'm assuming it would have to be the relief valve?
I went to a Kubota dealer to pick up a threaded plug for the hydraulic thumb cylinder along with a threaded cap for the hose. They pulled up the diagram & it doesn't show type or size. They had no tractors with hydraulic thumb on the lot. I called another dealer & they said the same thing. Does anyone here know the answer, type & size? If not, both dealers told me to bring in the hose to match it up. I would have thought it would be cut & dry. Oh well.
kubotafreak
Well-known member
Equipment
GRAND l6060, L3560, B6100, gr2100, tg 1860, g1800, g1900, g2160
I would guess it's JIC also. I took it apart & tried 1/2" American, close but it's not American. To the dealer tomorrow to get answers.
Half inch JIC is 3/4-16 UNF thread.
Even with a totally blown piston seal the thumb cylinder should produce something around 1500 pounds of extend force.
Dan
Thanks for the reply Dan. I tested the cylinder/piston today & it tested good. I re-connected the hose & ran the tractor at 1500 rpm. During the clamping of the thumb, I could still stop it anywhere including pulling it up at end of stroke. I'm not that strong. I wish I could get it to 1500 lbs of force, then I would be happy. Do you think if I took it to 2k rpm, it would help? Kubotafreak said it's probably the relief valve. It makes sense especially the way its acting. How do you actually test it besides with a gauge
Both dealers had no tees or gauges. I may have to get it.
Thanks
RPM is not going to help. A gauge is $20 plus whatever fittings but its probably going to tell you what you slready know - no pressure. My question is what relief are we talking about and why is it only the thumb with the issue?
Dan
Good question. Backhoe works great. There's a separate valve with foot pedal just for the thumb which I'm sure you know. My original post mentioned about removing the valve adjustment screw & add a shim (s). Yes, no, I'm at a loss. I don't mine getting a gauge & fittings, but like you said, there's very little pressure. Thanks again.
Actually I dont know but I will have a look at the parts breakdown in an attempt to educate myself. You seem to be indicating there is a relief valve just for the thumb which strikes me as odd. Is this a port relief perhaps?
Dan
Well that was a waste of time. I could find nothing useful in the way of a parts diagram for the hoe or thumb.
Got a picture of the valve? Is it a section in the main control valve?
Dan
I've educate myself to the fullest I can with everything I do. The Kubota OEM thumb kit is BT4598 (no pdf) for the L45TLB. According to the dealer, this kit is out sourced (NOT made by Kubota). They have one shitty picture of this kit that I found which is the same as the dealer pulled up. Dealer said there isn't even a thumb cylinder seal kit available! It's nice I don't need one. I'll figure it out some how.
Sorry for taking up your time.
I have tons of time so no need to worry about that. I found the shitty picture on the Kubota site and yes its worthless. A good picture of that valve might provide some insights....
This aint rocket science - you have a pressure source, a valve, and a cyinder. You can easily isolate the failing component with a pressure gauge.
- Disconnect hose feeding thumb valve and connect it to a 5000 PSI gauge. Start tractor and record pressure. That pressure is the maximum the tractor can supply.
- Reconnect pressure supply and disconnect hose going to base of thumb cylinder. Connect gauge to the hose, stsrt tractor. and operate valve to command extend. Observe pressure. It should be very nearly the same as maximum system pressure. Any difference is being lost in the valve.
- Reconnect base end hose and retract cylinder. Disconnect rod end hose and connect gauge to rod end port on cylinder. Start tractor and operate valve to command extend. Hold that command and observe pressure. It should be significantly higher than the base end pressure. If not the pistin seals are leaking. If it spikes and then drops to base end pressure its a slow leak. If it never gets above base end pressure its a massive leak.
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I was going to follow Dan's steps which makes common sense.
Before proceeding, I took a mirror & a light & found a second valve adjustment screw underneath the valve.
I removed cover, loosened & moved two 90* fitting lines just to get to the nut (still very tight) & screw. I used an extra long screwdriver to reach in from the bottom of the backhoe to get to the screw along with fighting with 2 other lines.
That seem to do the trick. I'll have to put it through a real test.
Thanks everyone.
Before proceeding, I took a mirror & a light & found a second valve adjustment screw underneath the valve.
I removed cover, loosened & moved two 90* fitting lines just to get to the nut (still very tight) & screw. I used an extra long screwdriver to reach in from the bottom of the backhoe to get to the screw along with fighting with 2 other lines.
That seem to do the trick. I'll have to put it through a real test.
Thanks everyone.
