I recently purchased a komatsu pc300lc-2 and shortly after buying it, it abruptly stopped swinging either direction. All other functions seem fine, fast and powerful, but it won't swing at all or make any different noise at all when commanding it to swing. I swapped the stick lines and swing lines on the left p.o.c. valve and have the same result stick works no swing. I then moved the lines on the check valve that is farther back between the poc and the control valve because I thought there seemed to be less fluid moving past that, (I didn't have any guages with me so I was just cracking a line), same results. I then started thinking I never really had more than oozing pressure anywhere so I went back to the gear pumps and cracked the lines and basically don't seem to get more than gravity pressure, minimal leakage engine off and ooze running. But,if there is no pilot pressure, it's strange to me the other pilot controls work fine and I'm getting nothing on the swing. I quit there to read the book and regroup. That being said I'm a retired Air Force electrician and hydraulic diagrams/ theory don't make as much sense to me as wiring does. I'm not sure if the lack of pressure I'm seeing is lack of pumping or a bypass somewhere. I don't think I'd want to dead head that little pump on that big motor seems like something might give in a bad way.
You will need to check the control valve spool that feeds the swing motor. First , is there pilot pressure going there, is there any pressure going to the swing motor. Some gauges hooked up will cost some money, but better than firing a parts cannon with no troublshooting. I have PC200LC-6 schematics and Hydraulic prints , but not a dash-2 machine. Maybe someone else will chime in with some info. Simon C
Good diagnostics so far! Here's what's happening: The "ooze" you're seeing at the gear pump is normal because pilot pumps run low pressure (30–50 bar), so cracking a line won't give you a dramatic spray. Don't dead-head it; you're right that it could damage things. Why swing is dead but other functions work: 1. Swing-specific pilot valve issue: The PC300LC-2 has individual pilot spools for each function. Your swing spool could be mechanically stuck or contaminated - even with good pilot pressure feeding the valve bank, that one spool won't move. 2. Swing lock valve: Many Komatsu excavators have a swing lock solenoid/valve that must release before swing activates (anti-swing safety). Check if it's: - Getting electrical signal (solenoid energized?) - Mechanically stuck closed - Plumbed correctly after any previous repairs 3. Swing motor brake: If the brake isn't releasing (mechanical or hydraulic release failure), the motor physically can't turn even with good oil flow. Next steps : Check for 12V at swing lock solenoid (if equipped) Test pilot pressure with a gauge at the swing valve pilot ports specifically Manually try to release swing brake if accessible The pilot pump is likely fine - focus on swing-specific components.
Thanks for your input. I totally agree with not loading up the parts cannon. A neighbor was adamant that it had to be the poc valve. But instead of just ordering a valve I switched the lines. I have some guages and fittings so I will try and figure out some test points asap. At least the swing spool is near the side of the machine. I will check pressure there. Thanks again
Thank you. I have hours staring at this book and I never noticed or read about that solenoid valve. Mainly because i got stuck on it being a pilot pressure problem and never traced that to the solenoid valve. I'll check that out ASAP. Thanks
Embarrassing but there is a swing lock button....
So it is swinging now , or you found button and it doesn't work. Operators Manuals are worth buying as NO ONE can know what all the buttons on a dash do exactly on every machine. Simon C
In my defense I never even got to run it. Bought it from a friend had it hauled to another friends farm that i have land attached to and he "broke" it.
Don't feel bad. I've had that happen a few times in my life.