Kubota KX91-3 Hydraulic Issue with Thumb

Was clearing trees the other day when the thumb stopped working.

Here are the symptoms: Trying to extend the thumb would get it to slowly move about an inch. The RPM at ¾ throttle drops about 300 when the extend button is pushed. Holding the button keeps the RPM low. Retraction works as normal.

All other machine hydraulics work fine. No visible leaks at cylinder or valve stack. Hydraulic tank at normal operating level.

Opened the fitting at the base of the cylinder and the thumb dropped with gravity. Let it fall about ½ way then closed the fitting and it still would not extend (close), but retraction worked normally.

The cylinder isn’t binding, nor is the thumb itself. I’m guessing it’s a valve issue but not sure how to verify.

Is there any chance there are shut offs/ quarter turn valves on the lines to the thumb that are on the dipper and one has gotten turned off?

That's a great question. There are valves on the dipper. The handles have long been broken off but I was working inside some saplings so one could have gotten snagged.

How about the valve under the cover at your hydro reserve tank. (4" or so silver lever) If it vibrated out of position the thumb starts acting up and won't properly function. I zipped tied mine in position after I had issues and figured out the valve was getting jarred with use.

Was the valve on the left hand side of the dipper. There was enough left of the broken handle to get snagged on a tree (I removed the remnant last night). Thanks so much for the help. Had visions of a $1400 valve floating around in my head.

Glad it was simple....I may have had that happen to me a time or two in the past....always check the simple things first