Changing the hydraulic oil on a Kubota B7510 HST
June 15, 2014
I just finished changing the hydraulic oil in the Kubota B7510. It’s quite a job. I’m told HST machines live or die on the condition of their oil, so it needs doing every 300 hours. The previous owner told me he had changed it just before I bought the tractor at 210 hours, but he apparently went by the manual and only changed the single filter mentioned there. That filter handles the lifting hydraulics. The other one (which the manual seems to have forgotten) handles the hydrostatic drive (HSD) It’s the one which gets all of the use on my machine, and it still had a factory black filter at 370 hours.
To judge from a lack of particulates in the oil and no evidence of metal filings anywhere, everything turned out to be in top condition, but to determine that I had to drain 11 litres of oil from the transmission case (from 6 different orfices: 6 potential leaks) and then pour new oil back in until it was full. The parts guy said its capacity is 13.4 litres, so he sold me 15. The manual said 13.4 litres for a B7510DT, but this one (HST or HSD, depending upon context) needs 15.3. It took 11.
The tough part was the strainer everyone warned me about. It’s a 26mm nut, factory-tightened very tight. Very few garage socket sets contain a 26mm socket, and none of the wrench sets do. I almost rounded the nut with a 27 mm socket when I removed it. Out the long, skinny cylindrical screen came, attached to the nut. I washed it, but it wasn’t dirty. I couldn’t find any metal fragments in the strainer, but the learning curve was a bit steep when I set out to replace the strainer. Eventually it went in easily if I lay directly beneath the assembly at the bottom of the transmission. This was not a bolt I could put in by feel alone.
I plan to check this strainer regularly from now on — about every 1000 hours.
The new, higher-quality oil from the Kubota dealer seemed to make the tractor quieter, and likely smoother. I’ll know better after a few hours of work. Update, 15 June: It’s certainly no quieter with the lighter premium oil, though everything seems to work well.
In retrospect, changing the HST oil was a messy job made tedious by the risk of a leak, but things went together quite well once I’d figured out how to do it.
A commenter on the Kubota page on Tractorbynet just told me that I missed one drain. That would account for the 11 litre drain and refill.
Next up is the front axle lube change. The same guy said that his machine weeped oil at the seals with the lighter oil, though it’s fine since he went to 90W gear oil, so I’ll try that.
Update: 19 December, 2016 When last fall I eventually drained the front axle lube, it was dark and burned-looking. I felt quite contrite about the oversight. The axle’s fine now, and properly filled.