Cat 320N 1997? 9wg serial series, i think maybe 0962 serial number Short summary: The left track is very weak. I was working with it and started losing power, worked just a bit more and it was terrible. Had the tech out and he found the relief valve had trash in it. Cleaned it out, now the power is good on the boom and right side, decent swing and very little power on the left track. Long version: I'm a farmer in central iowa, I have decent mechanical ability, but I am no pro, I bought this used machine last year, my first excavator with 8500 hours and was rode hard and put up wet. It tracked slow and the undercarriage was wore out. I put a new undercarriage on it and rebuilt the swing motor. That fixed the issues it had tracking. All went well this fall ripping trees out of fencelines and trenching in mainlines for tiling projects. I started it up one day and went to ripping trees. after about 30 minutes it slowed down a bit on the swing, nothing real bad, just barely noticeable. About 30 minutes more and it was real weak. I checked the oil level and bled the air out of the pump and all was fine, so i limped it back to my house and called Altorfer out of Cedar Rapids, about an hour away, He just happened to be going by so he swung in and found the screen on top of the suction in the tank was broken and appeared to let some metal into the pump which made its way to the relief valve and gommed it up. he cleaned that out and improved the situation, he cycled it and cleaned it three times, and checked a few other things. He didn't want to run it much without a screen, but did determine the pressures on what he called the regulators on the pump. the right was 4500 and the left 2200. He ordered parts and won't be back to work til after the new year. I got the parts.... a new screen and installed it, and also some orings for the left regulator. i took it off and rebuilt what I could, it wasn't fouled up, but i put new seals in it anyways and put it together. still weak left track. we tried a different relief valve and that didn't help either. I am assuming the screen housing that busted off allowed that metal into the system and plugged the relief valve but also plugged something somewhere else. I don't know where to look. Right now I plan on having the tech back out next year, probably will wait til spring or summer at the point so he has decent conditions to work it, but if i knew where to look to find an issue I would be thrilled to run down a problem myself, i am just not sure if its really doable for me or not. i was hoping you guys might give me a hint about the easy to check places before i start racking up an even bigger tech bill. I'm not opposed to paying altorfer their fair share, but i hate for it to be somethng easy we are overlooking, and it's currently driving me crazy that it's not like it should be.
A 9WG00962 s/n would make it a 1993 year build. Your machine is basically a pre-letter-designated Cat 320. Was available as a 320 (standard), 320 L (long undercarriage?) and 320 N (no idea!). To do that I think you're going to need some pressure gauges. The good thing is the right hand side is working properly, so you have something to compare it to. If out there fixing it I'd be asking myself is the left travel motor low on power or is the left track brake sticking? I'd be looking to see if there was I way I could swap the left and right track brake lines at a minimum. As for pressures... He may have been talking about the main hydraulic pump regulators? There's two pumps on your machine, upper pump and lower pump. Both are identical, both have regulators controlling pump output. Lower pump also has a pilot pump piggybacked onto it. Upper pump controls the right track and lower pump controls the left track. If the lower pump was only putting out 2200 psi, and you have changed some o-rings, you really need to see what it's putting out now. If the pump is failing that will put all sorts of things into the hydraulic oil you don't want. I'd be cutting open filters to check. But here's the thing. The lower pump will also be controling other machine functions independently. The online schematic in SIS is disgusting so I can't tell at a glance exactly which functions, and I don't have intimate hands-on experience with this model (if anyone does please chime in). Are there any other functions on this machine running slow?
its a 320 N which means narrow i do have some gauges, and it's humbling to say i didn't knew realize there was a brake, but i am just a farmer, can i pull hoses right at the final drive and compare right and left? yes the regulators right on the main hydraulic pump the oil is not glittery, but i can check filters, of course all this will be after Christmas, maybe even later than that because we are getting cold and wet, and i don't have a nice shop, so it's easier for me to do a thorough job with good weather and plenty of time The swing might be a little slower, but really everything else works fine, can you give me any hints about the brake, i will search the forums, but if you have more thoughts on what to check let me know, so right now it's just a completely useless left track
and thank you for you reply and effort to respond
Excavators have a hydraulic swivel, which transmits hyd. oil to the track motors.This allows 360 deg. rotation. The swivel has internal seals which keep the oil going where its supposed to. This is usually what happens to these machines.When the internal seals get blown out, the oil sent to the left track, for example ,short-cuts back to the hyd. tank via the case drain line. You can field test this by taking the lower end of the case drain off, and hold it in a 5 gallon bucket,and activate the left track.Oil will probably shoot out that hose.You may have to stall the track, by blocking the sproket with a large steel pin.If you get a lot of oil out the case drain hose, you will know either the swivel seals are leaking or the track motor is leaking/damaged. Its usually the seals,At least you will know what direction spend your money. Good luck.
The fact it's faulting on two functions that pass through the swivel (left track reverse & left track forward) would lead me to thinking swivel is not the cause. I mean it's possible, but wouldn't think it's that likely. Adam by all means do the field test DD57 described. Case drain is a good place to start, so is checking track brake pressure at the track brakes (you might need some adapters). You have a good side and a bad side to compare. You realy need a service book with this machine, for the hydaulic test/adjust procedures and the hydraulic schematic alone. I think I can hear Nige typing and looking it up now.
I think that's your biggest clue. After reading through the System Operations, it seems boom, stick and bucket functions use oil from both uppler & lower pumps, which is mostly dependant on your selected "power mode" and "work mode" settings on your monitor panel in the cab. From what I can see the Swing function only oil uses the lower pump, regardless of switch settings. And we already know the lower pump supplies the left travel motor, while upper pump supplies the right travel motor. Based on that it sounds like you have a lower pump issue, nothing else. Hopefully someone with more experience playing with these pumps can comment.
See where this lot gets you. Sorry the hydraulic schematic is a POS but it's all there is.
Isn't this a "each pump runs its own track" until an upstairs function (such as bucket curl) is used in conjuction, whereupon, one pump runs both tracks and the other pump runs the upstairs function? If so, tram straight ahead while operating the bucket in curl. If it's a travel motor issue, the left will still be lazy. If its a pump issue, both tracks will operate same while upstairs function is in use.
I couldn't find anything in the SysOps to support that, unless I'm blind, which is possible.
Never had tech time on an A model. My 322B and everything 320 or higher in B,C,D,E,F all do that.
Sorry I was blind. It's explained perfectly on pages 166 & 167 of the Hyd SysOps under "Straight Travel Control". Adam, what Heymccall said in post #9 above. Let us know how you go with that test.
You can get a flow meter with build in relief/load cell and pressure gauge from hydracheck.com and loop the two travel motor input lines together to see if your getting adequate flow at max specified pressure to the motor each direction. That's the safest and easiest way to tell if its something in the motor/brake valve or not. Best way to diagnose a hyd motor is actually by not testing it.