I have a Komatsu PC300LC-7 Serial 50161. What I do know is when you stretch the arm all the way out it does have a very very slow drift. My problem is when you stretch the arm all the way out and full stroke the joy stick all the way back, it goes about 1/4 of the way and the hydraulics seem to load up like its fighting something, you can even hear it in the engine a little. I did a little research, Im not very Komatsu familiar. I know I do not have the hose burst valve thats by the gland of the cylinder. On the base of the tube there is a block but that seems to be just a block for the two hoses to connect to. I do have a drift prevention device that's mounted on the control valve in mind. Ive looked at the schematics and its the only thing I could see that would possibly cause my issue. If any one can chime in on some more knowledgeable experience. I would appreciate it
I haven't worked on a Dash 7 model 300 but if the main control valve is like the Dash 6 machines there is a regeneration valve that is supposed to dump some of the oil from the rod side of the cylinder back into the piston side of the cylinder. We had some problems with those valves on the PC200-6 series machines back in the day. As I recall the valve was in the main control block and access was gained from the side between the valve and the firewall to the engine compartment. You will need a book to be sure of that. Too many old and tired brain cells to remember much of that time.
It happened suddenly or gradually?
I believe it was a gradually getting worse thing. Its my brothers machine. Ive been working on mainly cat and case equipment the last 12 years but just hardly any experience with komatsu let alone a problem like this. I also think its a faulty relief valve but i dont think it is cause theres no load on the hydraulics when bringing the arm in.
Check main pressure of arm in and also other function
I have the manual on PDF if you want. Send me your email