In have an old Deere 70d machinE Has tons of power in all functions. It has a thumb added by the previous owner operated by a toggle switch. It used to work fast now its very slow to open but closes fast and hard it has no loss of power. Now to close it I either have to rotate the cab while toggling then open function or curl the bucket. When I curl the bucket and operate the thumb to open it will open as far as the bucket will go and drop some when I un curl the bucket. No signifigant bleeding holding a log or a rock or any other load. Could it be the ram? The reason I ask is the thumb ram pins are really sloppy. But it still has full holding power. The relay or whatever that controls the thumb is mounted on the outer pump. The brand eacapes me. Blue writing on a metal tag and what appears to be a small 3 by 5 inch cannister filter connected to it as well.
Since it is a add-on I really can't be specific... other than to say check the filter, another thing about thumbs is they get beat up really easy... is the rod straight or bent?
The thumb is a home brew adapted off of a larger machine. It is straight and we put new bushings in The rod does have the tiniest crown in it but doesnt leak and works fine in one direction. Gues switching hoses is the next step.
Might be a bad piston seal in one direction, or lots of other things. If it's easy, try swapping the hoses to the thumb ram so the function reverses, see if the issue also changes directions, or not. If the problem stays the same it's the cylinder, if it swaps directions along with the hoses, then it's a valve or plumbing issue. Cheers
The nut or bolt that holds piston on the rod could be backing off.