Been using my R290LC-9 for some stump pulling lately. Had the thumb hydraulic actuator rebuilt about 2 months ago and it was working flawlessly until today. Yesterday -used thumb all day with no issues. Today, moved excavator to a new location in the yard and went to work only to find the thumb fully extended and will not retract - if I force it to retract with the bucket, it immediately returns to fully extended. I can tell when actuating the breaker foot valve that pressure is moving through the hoses (see them vibrate) but it still wont retract. It appears to me something is only applying pressure on the extend side of the actuator (and not switching to retract when called for.) Unfortunately, the schematic I have doesnt clearly delineate the sequencing of the actuator. Hoping one of you fine folks have some ideas as to where to start. Thanks for any ideas!
Their are 2 hydraulic options shown for the breaker/nibble circuit, one uses a foot pedal for double acting control and the other shows a solenoid valve for single acting on/off operation of the breaker valve. If by chance you have both types installed on the breaker valve circuit then the solenoid could be jammed on or powered on all the time, other possibility is a jammed spool.
Piston came off the rod.