I have a 2007 Komatsu pc78mr - 6 that I recently bought that has a hydraulic thumb. The excavator has a changeover valve, which as I understand, selects between breaker and two way flow on the aux circuit. On this valve there is an adjustable pressure relief but it doesn't seem to adjust cylinder relief for my thumb as I suspected it would (this is in the direct circuit I'd the hose going to the base of the thumb cylinder). On the main valve block I don't see anything adjustable on the section with my aux lines although there are a couple of covers that have springs under them and on another post on this forum a gentleman eluded to adjusting pressure by shimming. Does anyone know how to adjust the relief pressure for my thumb cylinder? As far as I know, all plumbing is factory on this machine. I've attached some diagrams from komatsu relative to what if found on my machine. Thanks!!!
Did you ever get this figured out? I have the same excavator and want to put a thumb on it as well.