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I have a Kobelco sk75sr, the machine tracking is sluggish…

Hi, I have a...

Hi, I have a Kobelco sk75sr, the machine tracking is sluggish also boom up is sluggish, and stick/dipper arm will not go out/away from cab, the machine is about 5500 hours old, is it likely that I need a new hydraulic pump or could there be other causes of these symptoms?

Mechanic's Assistant: What is the complete model and serial number of your machine?

Sk75sr, serial number YT07-25247

Mechanic's Assistant: Anything else you want the Construction Mechanic to know before I connect you?

That is all to start with, thank you

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Answered in 1 hour by:
2/13/2021
Mechanic: Dan, Technician replied 1 year ago
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 15,092
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
Verified

Hi, My name is***** will be glad to help. We can follow up as needed on here. Professionals are not employees of the site but users of the site and help on here as time allows depending on their daily schedule.Sorry to hear you're having these problems with your machine. I can understand how frustrating this can be when these problems arise unexpectedly. Since the problems are affecting both travel functions and your work equipment functions, it leans towards hydraulic pump problems. Remove the intake return hydraulic filter to inspect it internally for what looks like fine glitter in the oil and filter that would flag or confirm a pump failure or component failure existing. If this is found, you would need to start disconnecting hydraulic hoses to your components in order to look for contamination within your control valves, cylinders, hydraulic motors, and other components in order to determine the extent of the damage from cross-contamination. Any components that are contaminated need to be thoroughly cleaned out and in some cases resealed. This fine metal will embed itself into your piston seals in your cylinders and other O-rings and your hoses. The complete system would need to be flushed before running a new pump or component to prevent cross contamination and premature failure to your rebuilt or replacement pump as well as further damage to your hydraulic system components.If this is clean and no contamination is found, you will want to have your flows and pressures tested to confirm whether or not they are within OEM specifications and if not this could also lead to a pump that is in need of replacement based on these test results in comparison to the specifications for your machines model and serial number service book. In some cases there could be a problem within the main control valve or relief valve cartridges bypassing pressure. Thoroughly inspect your control valve spools and your relief valve cartridges for any type of scoring or damage, as well as damaged O-rings that would cause a bypass of pressure and the valves to malfunction. Your functions are split between two hydraulic pumps coupled back to back. One section of the pump runs one track while the other section runs the other. The rest of your functions between your boom, bucket, and stick circuit, are all split between the two pumps.I hope you find this information helpful. Reply back with the results of these checks if any further help is needed. It is a pleasure to help anyway I can.

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Customer reply replied 1 year ago
Hi Dan, Nick here, I have inspected the return filter and there is no sign of metallic particles thankfully, any suggestions as to where I investigate from here?Thanks for your assistance!Hi Dan, sorry, I only just read the full answer you sent, the sms was only half of your answer, I will begin inspecting the valve bank spools and the relief valve cartridges tomorrow, thanks again and will report my findings.
Best regards Nick
Customer reply replied 1 year ago
Adding to my first list of symptoms, the functions controlled by the gear pump are all working as they should, and I did notice that when tracking in a straight line there seemed to be a slight bias to one side like one track motor was slightly out performing the other one.
Do these symptoms provide any evidence for a more certain diagnosis?
Best regards Nick
Mechanic: Dan, Technician replied 1 year ago

Hi Nick. If you are having these travel problems that were just isolated to the tracks alone and all of your upper bucket functions were working normally, this would lean more towards swivel or Rotary manifold seals bypassing internally causing a loss of flow or pressure to your drive motors and ultimately causing your problems. This would be your most common cause of travel problems that is commonly misdiagnosed for a faulty drive motor. Normally a faulty drive motor would produce metal within your hydraulic system in most cases indicated by fine metal or debris that looks like glitter in the oil or filter just as a pump would. But since you are having troubles with your bucket functions as well, this flags a lot more potential to having pump problems or problems within the main control valve as I mentioned. Evidence of certain diagnosis exists after pressure and flow testing in comparison to the OEM specifications covered in the service manual. Certain diagnosis also exists, after checking for fine metal or debris in determining whether or not that exists in your return hydraulic filter and throughout the rest of the hydraulic system. Certain diagnosis begins to exist after process and elimination by analyzing data and test results.

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Customer reply replied 1 year ago
Unfortunately I can't get the diagnostic equipment to perform pressure and flow testing, I can also mention that the machine only tracked about 250 meters from being started cold and the boom and stick were operating (Just operating, certainly not performing as one would expect) after moving the machine the pump was way too hot for a machine thats only walked a short distance, and not done any digging, when started the boom would go up and down and after moving the machine it would barely lift up, I could hear the machine trying to load the circuit but there was no movement of the boom, and no noise like it was going over it's relief valve although it would still track but very slowly, once the heat got into the pump is it possible that the internals expanded and internal leakage was drastically increased to the point of severe inefficiency, possibly so worn it could barely do it's job? I do have some experience with hydraulics in earthmoving/forestry equipment and have encountered strange behavior due to valving issues, this sudden drop in performance seems to point to the pump, and from what I understand people like to get rid of midi/mini excavator machines at around 5000 hours because this is when the pumps start to under perform, I think I may have received one of these machines :-(
I don't have a service manual for the machine either unfortunately..
I have rebuilt/refurbished hydraulic pumps and motors before, so my next inclination is to remove the pump and inspect the internals and maybe even start pricing a replacement...This all happened shortly after the machine was delivered to me, the truck driver had just left and I had to move the machine off the road and into my property, it just seems the drop in performance correlated with the pump heating up to the point of barely being able to hold your hand on the casing without burning ones hand so it was over 60 degrees Celsius (I'm in Australia)
Mechanic: Dan, Technician replied 1 year ago
Thank you for the update and I agree that it leans strongly towards a pump failure.If it's creating that much heat you will likely see what looks like glitter in the oil and filter. Sounds like you're on the right track now.
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Customer reply replied 1 year ago
I do understand that you can't commit to an answer that says, "its certainly the pumps!" Without satisfying the need for the proper diagnosis, but your advice is very helpful and I appreciate it very much, thanks!!
Best regards NickThe filter pleats were dark in colour but no metallic particles at all, I even stuck my telescopic magnet in and all around the bottom of the filter housing but still could not find any metal particles stuck to it, I'm hoping I'll get out of this with a new pump, oil and oil filter (yes I'm a hopeful guy ha ha)It's raining now, so I'll be waiting for better weather until I resume my investigation...
Customer reply replied 1 year ago
The other symptom leading me to the pump, is the fact that the machine engine shows no signs of labouring and is far from loading up to the point of stalling when I fully load boom or track functions it just keeps idling/revving like it's hardly doing any work at all..
Mechanic: Dan, Technician replied 1 year ago
Thank you for the update. If there is any contamination whatsoever you will definitely want to make sure that all components are free and clear of contamination. Cross-contamination can cause any new replacement components to fail prematurely. I would also check your control valve spools and your relief valve cartridges for any trash or debris and any damaged o-rings or other problems that would cause them to malfunction. If this checks out okay I suspect that you are on the right track with a pump output problem.
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 15,092
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
Verified
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