Sumitomo 120-3 problems

Hi all my Sumitomo 120-3 is giving intermittent problems dealers cant find the fault, we thought it was the pump but that seems to be testing fine. it get slow when it warms up, I have to move the levers 5 or 6 times to get it to rev up on auto idle, it loses power when walking the longer I use it. all the temperatures are well with in the working range it some times makes a grinding type of feeling when slewing but the slew seems good I am wondering if it could be a problem with my pilot side of the system but am really quite lost. dose anyone have any ideas

Good day Erin
Suggest you test the pilot (Servo) pressure at low revs when the fluid is hot enough for the problem to show up.
Kind regards
Uffex

uffex said:

Good day Erin
Suggest you test the pilot (Servo) pressure at low revs when the fluid is hot enough for the problem to show up.
Kind regards
Uffex

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Thank you for the reply we have done this and it all seems to be where it should be. that's the hard part testing isn't showing anything wrong I am wondering whether I should start replacing stuff but don't know which thing first

Good day Erin
From your impression is that all circuits are on a go slow when the fluid heats up the servo pressure is good up to specifications, as long as there is no reduction in engine speed we would suggest that this is most likely due to main pump regulation, do you know if there is any temperature shut down system on the machine ?
Kind regards
Uffex

Erin Stables said:

Hi all my Sumitomo 120-3 is giving intermittent problems dealers cant find the fault, we thought it was the pump but that seems to be testing fine. it get slow when it warms up, I have to move the levers 5 or 6 times to get it to rev up on auto idle, it loses power when walking the longer I use it. all the temperatures are well with in the working range it some times makes a grinding type of feeling when slewing but the slew seems good I am wondering if it could be a problem with my pilot side of the system but am really quite lost. dose anyone have any ideas

Click to expand...

I would check in your Hydraulic tank for foamy, aerated Hydraulic oil .
If you have an air leak on the suction side of the pump, this will aerate the oil . This is the same as having air in your brake fluid in your car, spongy brake pedal with extra effort needed to apply the brakes .
If you are running a case drain from a motor type implement back to the tank, it MUST enter the tank BELOW the oil level or the same thing will happen .

I would also check the large rubber hose that comes from the Hydraulic tank and joins up with the bottom of the pump . They can get soft and suck flat when they warm up . They can also delaminate inside and a flap or bubble in the wall of the hose can form and restrict the flow .

The "grinding sound" you hear when slewing is either the slew brake dragging because of low oil pressure not releasing it fully, OR it could be air in the system growling, but I think it is the brake dragging .

If the oil is not getting hot, it is either aerated oil or the large suction hose as I mentioned .

For some strange reason, Sumitomo used screened fittings on all the inlet lines to their pilot controls. The last one I worked on that had hydraulic issues, all the fitting screens were plugged up.

Have you check you alternator output voltage? The slew brake is affected by one of the wires coming off of the alternator on the older Case and Link-Belt lines.

Thank you all for your replies am still going on this one now when it is warmed up it will not turn. Walks ok when both tracks are going but stop one and the other has no grunt any ideas. Found the strainer washers one was broken

Good day Erin
Here is some trouble shooting information while it refers to crab crawling the same method may be used for your situation it may help.
Kind regards
Uffex