Problem we are experiencing is the thumb will push the bucket back. The thumb is a CF with a mechanic coupler from Woods Equipment. It has done this from day 1. Relief cartridges are installed, so we tested the bucket cylinder and it leaked fluid back when it should not. We had the cylinder tested by a rebuilder, they found nothing wrong but still rebuilt the cylinder to be sure. Reinstalled the cylinder and lowered the thumb pressure down to 700 psi. Now the thumb will not push the bucket back but now loosing thumb strength. According to Doosan and the thumb manufacture we should not have to do this. Any thoughts ........................................
Be Careful I work for a US Manufacturer of Excavator Thumbs and Buckets. (Not any company you have listed.) The Standard practice within the industry with Hydraulic Thumbs is pressures are to be set where the Bucket will always over ride and push the thumb back. So if the thumb and the bucket are pushing against each other the bucket will over pressure the thumb and the thumb circuit will allow the thumb to be pushed back by the bucket. Failure to have this set up correctly leads to you guys all buying expensive repair parts from my parts guy! Consult your thumb installation manual for the suggested pressure. Good luck. Mr.Mel
Another quick point. To test your thumb cylinder retract the thumb and shut the machine off and let it sit. If the thumb drifts down your cylinder is leaking externally, internally or your Thumb circuit is leaking. You can disconnect the lines to the cylinder and plug the ports and perform the same test and if it then drifts down you know it is the cylinder. Be safe please. Mr.Mel
Thumb hydraulic relief pressures in general are set at approximately 2,100 PSI on the piston side and 2,400 on the rod side. I think the bucket circuit should be somewhere well over 4,000 PSI. If you blowing over the bucket circuit with the thumb and the cylinder is OK, then you have a circuit relief issue on the bucket circuits.