Hi folks I have a hitachi ex120-2 that I just bought and after ten minutes of running starts playing up. If I slew around it will stop and start with vibration. If I dead head any service like fully close the bucket it will start vibrating pipes. It’s symptoms are like a machine low on hydraulic fluid. It does not stall the engine. I have replaced the exhaust and throttle cable,all new filters and oils. The fault was on it before any work was done. I was told to do a conversion on the sensors but I’d like to investigate a bit more. Any information would be appreciated
Is the machine performance fast and with no vibration if tracking at full speed or stroking the boom or arm cylinders in the air at full speed ? The vibration at slew (swing) stop and start sounds like the swing brake is slow to release and quick to apply. Eliminate the swing brake function completely ( as a test only ) by unplugging the solenoid in screenshot below. See if it resolves the swing vibration at stop and start issue.
If tracking at full speed yes this will happen and it happens while in the motion of swinging and other functions. I’m going to double check the boom and arm but I think it’s the same. I taught it might be a main relief valve myself? Thanks for your quick reply
If the vibration exists when using any functions including when not dead headed leads me to think it is not a main releif valve issue. Sounds like the pump is starving for oil. The hydraulic tank normally becomes pressurized after a few cycles of raising the boom to full height and back to ground. After cycling the boom a few times , turn the engine off , remove the hydraulic fill cap and listen for a “whoosh” sound as the air pressure is released. If tank pressurization proves ok, check for a restricted suction screen located in the hydraulic tank.
I just went back to the machine to double check. If I try to slew normally it starts vibrating but if I ease it into it,it doesn’t. Same with boom ,bucket dipper. I should have said I changed the suction,return and pilot filters and new oil as I originally taught it was a restriction. There seems to be a bit of air/bubbles in the hydraulic tank. If I stop and leave the machine running,it will work ok again for a couple of minutes.
Sounds like air is getting sucked into the system somewhere. I'd start by checking the suction hose for any cracks, loose clamps, or fittings that aren't sealing tight. Even a tiny gap on the suction side will pull air in under load. That would explain why easing into movements helps and why it settles down after a rest. Also, worth checking the pump shaft seal. If it's leaking air past the seal, that could do it too.