CAT 320N weak tracks, won't turn

[Ace]

I have been searching through the posts on here trying to find someone that is having the same problem as I am but nothing yet and I am stumped so hopefully someone can shed some light on what's going on. About 6 months ago I bought a 93' or 94' CAT 320N serial number 1XM00141, I have owned several backhoes and a dozer but this is my first excavator. When I bought the machine the tracks were a little weak. A friend of mine who was a former CAT mechanic told me it was most likely swivel seals so I took a chance on it. I have replaced those and it did not change any. It will go ok when you run both tracks the same direction at the same time (straight line), when you run only one track at a time it will not hardly turn the track. When you run both tracks in opposite directions it will spin but very slowly. It does seem stronger when the oil is cold and gets weaker as it warms up. All other hydraulic functions seem to be ok, the machine digs fine. It is mainly a farm machine but I do some for hire work on the side. I have put maybe 70 or 80 hours on it in the last 6 months so I have just been using the boom and bucket to help turn and working with it until I can figure this out.

Here is where it gets complicated, around 3-4 weeks ago I was running in a fencerow and had been working the machine all day long. As I was working on the last couple trees I lost all digging power, it would stall the engine when you put the bucket in the dirt, ....but the tracks came to life! It would spin in circles and throw mud running just one track but it would not dig at all. Even raising the boom or curling the bucket would stall the engine but the tracks were running better than a brand new one. I parked the machine and found out the next morning the batteries were drained, 9-10 volts on each battery. They were brand new so I tracked down that the alternator was the culprit. I replaced the alternator and charged the batteries and it started digging fine but the tracks were back to being weak again. In case you were wondering the fuel shut off and throttle are manual now, so I had no idea the batteries were weak until I started it the next day. The shut off was bypassed before I got the machine and the auto throttle stuck on me one time in the middle of a job so I unhooked it and rigged up a throttle assembly from an old ford tractor and got working again manually. I called my local CAT dealer and had a service guy come out to see what he could find out. He was there for 3 hours and tested pressures on the pump and voltage to some solenoids but said he could find no problems. When he left he was leaning toward a wiring harness but could not say for sure. He said with the fuel shut off and auto throttle bypassed he could not accurately test the harness. They were getting me a price on a whole new wiring harness but I have not heard back yet. It is a 20+ year old machine so I don't doubt there are some rough spots in a few wires but how could it switch when voltage got low then go back when it was charged up? It may very well be the harness and I am not a Cat mechanic but it just seems like a solenoid or valve would be more likely to cause those symptoms of it coming and going under low voltage? I just don't know where to check or what wires to look for that would control those functions. Any input is greatly appreciated. Thanks

 

[Bob/Ont]

At first I thought you didn`t do a good job of the reseal of swivel but the more you said it sounds like a wiring problem. The machine has a computer controlling pump flows and bad wiring could tell the pump to reduce flow at the wrong time.
Later Bob

 

[overworked]

Sounds like a prv issue, when voltage was low the pumps were staying up stroked, causing the stall? More flow of oil to travel motors. Without knowing what engine rpm your running, computer wise you have no control of pumps or digging modes. When you rebuilt swivel were there any seals in it when you took it apart? Most likely have more than one problem now they are starting to pile up on top of each other. I would suggest to start with throttle control.

 

[Ace]

When I redid the swivel there were old seals still in there, they we're hard and cracked up but mostly intact. I would like the throttle control to work but I'm stumped there too, it has a new $1100 throttle motor on it, the dial in the cab seems to be working cause the numbers on the display go from 1-10 as you turn the dial. When it quit the machine was at about half throttle and it just stuck there. I checked the ohms on the speed sensor and it checked within spec. Also the manual switch behind the armrest did not do anything.

 

[Bob/Ont]

The manual switch still needs to feed it's signal down the wires to the control.
Later Bob

 

[Mobiltech]

The mechanic should have done a PRV calibration or a sweep test to see what the pump controls are doing.

 

[Ace]

I don't know what all tests he ran? He hooked gauges up to test ports around the pump but I was not there for the whole process so I don't know what exactly he did. I have heard a little about PRV solenoid issues through reading some other posts on here, are those the two blocks on the left side of the pump? What exactly do those do?

 

[Huntoon]

Just a stupid guess: maybe the travel motors are stuck in low displacement (high speed) mode? This could limit the torque available for turning.

 

[Mobiltech]

The prv is on the pilot manifold down to the right of the pump .It will have a round black ball shaped accumulator next to it. The prv is the solenoid valve that the electronic control uses to adjust pump flow . It sends a modified pilot pressure to the pump. This valve requires calibration sometimes and if calibrated the right way ( lower than spec ) it will really affect the speed of the machine.

 

[humboldt deere]

I had a 94 312 until recently and went through all this. My PRV was bad it was only around $250 to replace. If you decide to replace the PRV then do a stepper motor calibrate, and sweep like mobiltech mentioned. My machine ran very poorly, but after new PRV, stepper motor, and some pilot pressure sensors, I calibrated everything and it ran great. I wish I still had the calibration sequence, but it went with the machine. I do still have a code book for your machine, so if you do a code scan I could help you with what codes come up. Also on just answer theres a guy Catmastertech that helped me out a lot, he's very good with that series of excavator.

 

[newguy2k3]

Just a stupid guess: maybe the travel motors are stuck in low displacement (high speed) mode? This could limit the torque available for turning.

This is my hunch also. A PRV problem would affect every function. Every Cat excavator I've seen requires pressure to move the travel motors to low displacement/rabbit mode. The smallest line running through the swivel will be the one to the travel motor speed actuators. You could try to plug it and see if anything changes.

 

[lantraxco]

If the battery voltage dropped low enough, the solenoid valve for the two speed might drop out. Maybe it's an electrical problem.....

 

[catman13]

It may be a prv problem but it may be a wire problem, a friend of mine has a corn picker that is all electric /hydraulic like an excavator, and he found it had a low voltage problem to cab and it was messing up the control of the machine fixed the wiring problem and replaced some relays and it fixed the problem , and you have a problem with throttle & shut off already ......just my 2 cents

 

[Ace]

It still switches from high to low range now, it is definitely weaker trying to turn in higher range. But you can feel it change as you are going. Another thing I will throw in is that when it had the low voltage problem and the tracks were working right it was stuck in high range and would not switch back to low. When the batteries were charged and the new alternator put on it would switch back and forth from low to high again like it's supposed to.

Also the track issues were going on before the throttle and shut off quit working. So I now those are a problem but the tracks were messed up when those were still functioning properly. I talked to the previous owner and he told me the tracks were still messed up before the fuel shut off quit on him and the throttle messed up on me after putting 30 or 40 hours on the machine with the tracks weak.

 

[newguy2k3]

Is the straight travel function working right? Can you travel straight and then use another hydraulic function and it still tracks straight?

 

[nathanbradley23]

Hi I'm have a 1995 cat 320n that have the same problems. Wondering if you found out your problem yet? Getting ready to tear into ours and try to fix it. Been running it in manual pump mode for a while.now but its starting to bog down in it too? Any help would be great.Thanks nathan

 

[Ishq]

Travel Motors normally passes through swivel joint. And if the rest of the excavator is relieving at 330Bar or more and the motors are not producing more than 200 to 240 bars, normally seals are gone.

 

[nathanbradley23]

Hey thanks for the reply. We did some troubleshooting wi th the service manual. Turned out to be a bad controller. Replaced controller and done the calibrations. Runs like a new one except for the rabit function on the tram. Dosnt want to switch into high. Low trams good now better than ever. Not sure may be the selnoid. Will change it and see.