Komatsu PC120-2 travel motor issues

[125IIIA]

Hey Guys,
I have a Komatsu PC120-2 SN 16129 It's a late 1984 or early 1985. The right side track motor has been getting slower and slower since I purchased this unit about a year ago. When the hydraulic oil is cold it isn't to bad but as the oil heats up it gets a lot worse. It is just as bad if not worse in reverse. I pulled the return line off the travel motor and ran it at full throttle for one minute with hot oil and the track stalled and got 23 ounces from the right and only 4 ounces from the left side with the same test. I believe it's the pistons, shoes and cylinder inside the pump that are worn. I have the shop manual but there are no specs for such a test. I preformed the leak test in the book and the motor passed. That test is basiclly the same but you let the track rotate freely in the air for one minute. Does anyone have something else I should look at before I order a $3000.00 used final? There are no parts or rebuilt finals for this machine out there that I can find. The motor is a Teijin Seikco GM15G-A-78 The excavator has 6000 hours on it and I have rebuilt the swivel joint and did a few other checks before finding the leakage in the travel motor. Thanks for the help,
Matt

 

[lantraxco]

Have you checked pressures, could be weak relief valves.

 

[mikebramel]

I don't unerstand why you would buy a used final drive when you have demonstrated there is a lack of flow from the pump? You did mean return line off the motor and not the case drain?

 

[John C.]

I am assuming you are checking motor leakage at the case drain line and not one of the supply lines. To check them properly you have to put a pin in the sprocket and rotate the pin into the track frame. Then check the case drain with the engine at high idle and the pump in maximum mode. If the motor is bad you will get a gusher.

The center swivel is a much more likely place for oil to leak by than the travel motor. Also as I recall on those models the travel motor is separate from the final drive.

How do the rest of the functions work? Have you run any cycle times, boom up usually tells you the most. A Dash 2 machine uses all manual linkages to actuate the valves. Are you sure you are getting full stroke on the slow side? Look for worn pins and bad holes in the links that connect from the levers all the way back to the valve spools. The pumps could even be out of adjustment.

The Komatsu manuals are usually pretty comprehensive in describing the machines once you learn how to read them. I believe they were written by an engineer for an engineer.

Good Luck!

 

[125IIIA]

Thanks for the responses guys,
I havent checked pressures but did swap the relief valves around and it didn't make any difference. John, I am checking motor leakage at the case drain and not the supply lines the same as you described above. The swivel joint has been rebuilt and the linkages are all working correctly. The Komatsu manual for the PC120-2 is photocopies of photocopies and also missing all of the hydraulic testing and troubleshooting sections, it was so bad the my dealer said it was useless and let me return it for a full refund and let me keep the PDF version.
I don't know what cycle times are or how to test them but all my other functions seem to work fine, it is a older machine so I don't expect it to be as fast as todays machines.
I guess my question is this, the slow side final drive motor has a leakage rate of 23 oz a minute and the good side is only 4 oz a minute (hot oil, stalled track, full throttle) can this be anything besides a bad axial piston pump in the final drive? Thanks again, Matt

 

[sultan]

I initially suspected your centre swivel, and it could still be that. Even though it has been rebuilt, try swapping the lines at the swivel just to rule it out with certainty.

Seeing that the bad side's case drain dumps 6 times the volume put out by the good side, it's likely that the track motor is at least partly responsible. However, for a failing track motor, I would have expected even more than 23 oz/minute in the case drain for a noticeable slowdown.

I'm not familiar with your machine. Does it have high/low speed ranges for the track motors? (most modern machines do) Is the problem noticeable when tracking at low speeds, or is it at high speeds only? If the problem only occurs at high speeds, it could it be that the bad side is remaining in the low range while the other side switches to high range.

P.S. By cycle times, John is talking about the time it takes for the machine to perform an operation such as fully curl the bucket or move the stick from all the way out to all the way in. There should be specifications available for the time these operations take. These timings can be used to check if the pump is putting out the correct flow.

 

[finaldrive]

23oz compared to 4oz on case drain test, and your low performance when oil is warm, is classic case of rotating group being worn out as you suspected in your first post.

Click my links below and go to Service section

 

[John C.]

When I have had hydraulic motors leak by, the case drain flow was in the gallons and not ounces. I have seen lots of damage to rotating groups from foreign material but not seen one worn out. Leakage is usually a result of wear between the end of the barrel and the output plate. Lapping the two parts together and putting the motor or pump back together is usually all that is required. That isn't that hard to do but rebuilders will want to sell you new rotating groups.

I asked about the cycle times because there is also a possibility the pump feeding that track needs to be adjusted to balance with the other. That may or may not be possible to do as the control valves will be worn and it will be hard to find parts for this particular machine. Last time I checked Komatsu quit making parts for these and all you will have access to are those items still on someone's shelf. As old as this machine is you could spend thousands trying to fix a problem that isn't worth or possible to fix.

 

[125IIIA]

Well I swapped the lines at the center swivel joint and the slow track switched sides. After that I swapped around the lines that leave the hydraulic pumps on the back of the motor and the slow track switched sides again. Worn out hydraulic pump right? It's worth noting that my pumps that are driven off the back of the engine are all gear pumps. Thanks guys.

 

[125IIIA]

Got some hydraulic pressure gauges this week and hooked them up at the test ports on the pressure lines leaving the gear pumps on the back of the engine today. They were both set high so I got the two main relief valves set at the 2500psi per the shop manual. In reverse the right side tracks fairly straight now but forward is still bad. When I switch the lines leaving the gear pumps the slow track switches sides. Can I have correct pressure and incorrect flow on a gear pump? I have no way to test flow but the manual says 32.5 gpm if I remember correctly. Cycle times are all within spec with the exception of bucket dump and it is 0.5 sec slow, bucket curl and dump are on the same gear pump as the right hand travel (slow side) Thanks again

 

[mikebramel]

Your cycle times are measured unloaded with very little pressure. The track test is loaded. You have already determined the problem most likely to be the pump. The only 100% sure absolute way is to flow test it. Which around your area will cost???? Around here $200

 

[125IIIA]

Mike,
Yea I'm checking cycle times with no load and tracks stalled out all at full throttle. I have to be 100% sure as the bank of three pumps is $4200.00 The closest dealer is over a hundred miles away and it sounds like all drive time is billed. Buying a flow rater and having metric hyd lines made won't be much cheaper but at least I would have a flow rater. So I should have the pumps flow rated for sure before I order a new pump set...? Thanks