I have a 2001 PC78US-5 excavator. Gray market machine with 6500 hours. The arm-in function is slow, all other functions are normal. Should I start by checking spool valve on the main valve block? Or could it be a pilot control issue? Does anyone have a repair manual for this machine or any diagrams of the hydraulic valves? Thanks, Jake
Update: problem solved! Checked pilot pressure by switching bucket and arm pilot lines. Problem stayed with the arm-in function. Removed caps and springs from main valve body and found that the arm spool was stuck. Removed the spool, cleaned it and put it back in. Arm function returned to normal!