I have a Komatsu wa400-5L. After running for 30 minutes the bucket dump slows way down, to the point where I almost have to have the throttle pinned to dump. sometimes at idle the bucket won't even move to dump. Lift and lower seem fine, curl up seems fine as well unless its a real heavy load. I have noticed that they don't seem as strong as before. The fluid is new (blew a 1.5" line) and new filter in top of the tank. Problem started before I blew the line. A plugged screen, valve , solenoid? I do have the service manual but looking for a starting point. Thank for any help or input.
sound like the seals in one or the other cylinders is bypassing internally
wouldn't make it slow all the time and not after it warms up good?
Hot oil thinner, bypasses easier.
Something my dad taught me about hydraulics is speed is to flow and power is to pressure. If you suspect bypassing cylinder you can stroke out the cylinder to the end of its stroke. Then take the line off the end that is not getting oil from stroking it out and if you have oil spraying out then your piston seal is blown. But if that was the case then you should have drift in the cylinder and trouble with both directions. Sounds like a flow issue. Find the valve controlling the bucket and take pressure readings on both sides. If you’re not mechanically inclined and can’t do this without hurting yourself and creating damage to the equipment then call a professional.