Tractor Repair: hydraulic problems, kubota l3400, oil starvation

Question
I have a 2006 Kubota L3400 HST 4x4 with 175 hrs. I started it up and the implements Backhoe and front-end loader were moving real slow and jerky. The machine would actually shake when the movement was not smooth. I looked through the sight glass and it appeared that the fluid was all foam. I drained all the hydraulic fluid and changed the hydraulic filters. I found nothing wrong with the old fluid. I used all Kubota oil and filters. Started the tractor back up to manufactures specs. I am still having the same problem. The fluid in the sight glass seems to disappear and foam covers the sight glass so you cant even see in there. Any info would be greatly appreciated. Very mechanically inclined. Just not good at all with hydraulic problems.

Thanks Bob

Answer
Hello,

  If the fluid level is full up to the sight glass with the engine not running, then it's filled to the proper oil level.  If it's still foaming and jerking with the oil full and new filters, then you've eliminated the possibility of oil starvation, and the pump is sucking air into the hydraulic system through an air leak on the suction tube to the pump.  Possibly a bad o-ring or seal??  Don't keep running it that way, as cavitation can damage the pump over time.  It is normal to see the oil level drop slightly and see SLIGHT foaming of the oil with the engine running, but if it is excessive as you describe, the oil is being aerated from the suction leak and is causing the jerky hydraulics.  If you can't determine the cause of the suction leak, I would suggest getting it to a dealer for service soon, because running it this way could damage the pump.

                  Good luck,

                       Arnie