I have a PC300LC-6. I had trouble with the arm cylinder and had it rebuilt. ( the snubber came loose from the piston and beat things up pretty bad. some small peices went down stream.) The arm still drifts both out and in. Any I deas what to look at next?
Port relief valves for the arm spool, and then the spool itself. Could have some debris lodged in there somewhere.
Does it have a lock valve / quick return?
I am not sure what a lock valve / quick return is. This is the first Komatsu I have owned
OK so I am still fighting this problem. I have tested the rebuilt cylinder and believe it is ok. I have swapped the suction safety valves for the arm spool and nothing changed. The spool looks good and floats freely. It does have a quick return valve. Note: When I shut the unit off with the arm extended, I can hear fluid leaking by in the arm spool valve area.