John Deere 855 Hydraulic Problem

jimsing · May 3, 2023

Hi all, I have a JD 1998 855 25 Hp hydrostatic drive and when the tractor gets hot, the transmission slips but the front end loader works fine. I changed fluid, filter and cleaned the screen, which looked good, and that didn't help. I then put new O-rings in the pump and that didn't help. I then changed out the hydraulic pump with another used pump and it helped some but it still slips once you work it hard for half an hour or so. Any other thoughts outside of taking it to the dealer and letting them have their way with it?

Would changing over from HyGard LowVis to HyGard HighVis help?

Thanks in advance

Dave M7040 · May 9, 2023

In a hydrostatic transmission the main tractor hydraulic pump has next to no involvement in the HST operation.
Suggest you post in a JD section of this forum as your problem is really not hydraulic
Dave M7040

Leejohn · May 9, 2023

Hydrostatic transmission might have a charge pump.

jimsing · May 10, 2023

Dave M7040 said:
In a hydrostatic transmission the main tractor hydraulic pump has next to no involvement in the HST operation.
Suggest you post in a JD section of this forum as your problem is really not hydraulic
Dave M7040

Thanks Dave. I think we've figured it out. I replaced the HyGard LowVis with 15w40w oil, suggested by the local JD dealer, and it seems to be working a lot better. At least for now.