hi we have a komatsu pc 400 lc-8 with very bad stick/arm cyl drift also seems to have low power in the stick function as well, I have checked the main pressure at the pump and it is 5500 psi , anything easy to check swap something with other side of circuit ? I have no manuals for komatsu equipment . Any help would be great thanks .
Sounds like internal leak in cylinder
Over load relief valve for arm/stick circuit, then again you wouldn't be seeing 5500psi at pump while stalling arm/stick if it was leaking.
Depending on the amount of leakage in the cylinder you might be able to hear a hiss in the barrel when hold the function over relief. The circuit relief can also be a problem at times. Do you know if your machine has load lock valves on the stick and boom? Those machines are closed center load sensing so the pressure you see at the pump will not be affected by a little leakage in the cylinder.
Cheking for cylinder internal leakage is the fastest and cheapest to start with, before you check the rest of the circuit
No lock valves on this one, I'll try to listen in the cylinder , and check the return filter for any sighn of seals. Machine has 14,500 hrs .
Are any of your cylinders leaking at the packing? Do you know the last time any of the cylinders were repacked? That stick cylinder is way up in the air so you might want to try checking it a different way. You can stretch out the stick and set the bucket on the ground. Relieve all the pressure on the stick cylinder and then relieve all the pressure in the hydraulic tank. Disconnect the rod end hose at the control valve for the stick cylinder and cap it and the outlet port on the control valve. Next disconnect the piston end hose at the valve and set it into something that will hold a lot of oil. Cap the outlet of the control valve. Now you can start the machine and very slowly pick up the boom without touching the control for the stick cylinder. If the cylinder is bad the stick will drive down and you will get a bunch of oil out the piston side of the cylinder into your receptacle. How ever you do it go slow and careful. That is a lot of machine and getting hurt is real easy to do.
One of our 345s was doing the same thing. Had both boom cylinders rebuilt. That fixed the issue
We got the hoe last year so no info or service history we run mostly cat equipment , think I'll go with johns idea. No external leaks anywhere on the cylinder.