Hey everybody I have a cat 318c excavator serial# CAT0318CLMDY00251 and the thumb is closing really slow/ won't hold anything. Also if you have the boom up in the air with the stick extended straight out it will only close half way and then stop. I can get it to extend all the way out if the stick is pointed down but as soon as you straighten out the stick the thumb will bleed off to half way even with the button pressed to close it. All the other hydraulics are fast including the thumb open. Also as a side note it has a foot pedal that is supposed to operate the thumb also. Unfortunately it will only open the thumb and not close it for some reason. Ive looked for a ball valve that would control the single action, double action functions with the thought that it was partial closed/ opened but I have yet to find one. This has really got me stumped and since the work I do requires using the thumb about 80 percent of the time it has almost completely shut down operations. Any help or advise anybody could give me would be greatly appreciated thank you.
Has it always been this way? My C models have electronic relief settings. A thumb, however, may have an additional conventional mechanical relief. Can you pressure test the circuit?
Would this happen to be a gray market machine?
Not gray market... That machine has electronic two pump, two way, tool control. It sounds as if you don't have the proper attachment tool setting selected. So, what tool setting is selected? Do you know how to change tool setting selection? I don't believe thumb is one of the five "default" tool selections. Did your dealer program one of the selections specifically for a thumb? Being in a one way tool program (cvp 80, h110, etc) will disable the second direction on the foot pedal, and explain the drift off the thumb. "Shear" would be the closest "default" setting for a thumb.
Here's the drill down for the monitor
I would eliminate your cylinder bypassing internally to start. It’s easy to check. I don’t know how that cylinder is mounted. But if you extended all the way and then remove your retract line. Then hit your switch and keep trying to extend it. If you are continually getting a lot of oil out of that retract port when your actuating the extended port then your cylinder has a bad piston seal. If that’s fine then install a gauge in both lines and see what pressures your getting and make sure they’re not intermittent.