I have a Case 580 SM and a BIC (Burlington Installations) auxilliary hydraulic kit was already installed when I bought it. It is double acting and controlled by a toggle switch on the backhoe boom control lever. I just built a hydraulic thumb attachment and installed on the backhoe - It worked great just moving the thumb back and forth but the first time I closed the backhoe bucket against the thumb it bent the thumb cylinder rod (a 1.75" rod). The relief valve setting on the BIC control valve must be set too high and it doesnt allow the thumb to open if the bucket pushes against it too hard. I dont have a manual for the BI auxiliary valve and not sure how to adjust the pressure relief setting. Appreciate if anyone has the info could give me some info on how to adjust the pressure relief so I dont bend another cylinder rod. thanks Gary
Part of your problem is that the thump cylinder should match the bucket cylinder. IMHO. The bucket has a 2.5 inch rod. The 1.75 rod in the thumb cylinder is kinda wimpy to interact with the bucket. The relief valve will need to be pretty low so it will allow the bucket to push it closed when the need arises. Sorry, I didn't answer your question. On my backhoe I matched the cylinders rod size and the thumb pushes the bucket open effortlessly. The bucket cannot push the thumb cylinder towards closed. Not even a fraction of an inch.