DrBT
New member
Equipment
ZD25 zero turn, M5700 Kubota tractor, Brush Bull Rotary Mower, 72" grapple
2005 ZD Hydro problem
- Thread starter DrBT
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whitetiger
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Staff member
Equipment
Kubota tech..BX2370, RCK60, B7100HST, RTV900 w plow, Ford 1100 FWA
The latest version from Kubota for a ZD25 is all that will fit. What is wrong with the Hydrostat?
DrBT
New member
Equipment
ZD25 zero turn, M5700 Kubota tractor, Brush Bull Rotary Mower, 72" grapple
My ZD only has 500 hours on it and has been meticulously maintained. The Hydro started to chatter and grab and reverse on the left side only works if the right side helps it to move. I tried purging air out of the system, with no avail. I can hear what sounds like a rush of fluid under full forward or backward that I never heard before. I took it to the Kubota dealer and they didn't find anything wrong but charge me $200 to tell me that. The other Zero Turn companies in the area won't touch Kubota.
you need to know what's going on with it before replacing parts
first, remove the screen from the bottom of the transmission and see what's on it. If you find brass shavings on it, you will be replacing one of the hst's, or perhaps both. If aluminum, charge pump is likely--replace it first then see how it acts.
if u find brass, pull both hst's off and disassemble them to find the problem. If you have to rebuild them, or replace them, go ahead and replace the charge pump too. Get a workshop manual! It is required for a repair like this and yes, I use it often even after doing a few dozen of them.
that's about the best I can tell you without putting any pressure gauges on it
I've done all sorts of different repairs to the hst's pumps, motors, axles, brakes, hubs, seals, bearings, etc on ZD25 and ZD28. The Newer version (ZD3xx series) is completely different, much better design by far
Kubota used to have a kit for the ZD25/28 that increased the fluid capacity, and that seemed to help but was only prolonging the inevitable. The books don't tell you this but whatever the HST fluid/filter service interval is, should be cut in half for the older ZD series with the exception of the ZD18, never had a minutes' trouble out of the little ones for some reason. Always the 21/25/28 and mostly the latter two. Nobody knew there was gonna be any issue with them until they were out for a few years then problems started popping up, mostly in the Southern USA, with the heat of summer (normally). Heats the fluid, not much of an oil cooler, not a lot of oil capacity, small (ish) charge pump, only one filter, they were fine in Japan where they were designed & tested, but apparently not here.
first, remove the screen from the bottom of the transmission and see what's on it. If you find brass shavings on it, you will be replacing one of the hst's, or perhaps both. If aluminum, charge pump is likely--replace it first then see how it acts.
if u find brass, pull both hst's off and disassemble them to find the problem. If you have to rebuild them, or replace them, go ahead and replace the charge pump too. Get a workshop manual! It is required for a repair like this and yes, I use it often even after doing a few dozen of them.
that's about the best I can tell you without putting any pressure gauges on it
I've done all sorts of different repairs to the hst's pumps, motors, axles, brakes, hubs, seals, bearings, etc on ZD25 and ZD28. The Newer version (ZD3xx series) is completely different, much better design by far
Kubota used to have a kit for the ZD25/28 that increased the fluid capacity, and that seemed to help but was only prolonging the inevitable. The books don't tell you this but whatever the HST fluid/filter service interval is, should be cut in half for the older ZD series with the exception of the ZD18, never had a minutes' trouble out of the little ones for some reason. Always the 21/25/28 and mostly the latter two. Nobody knew there was gonna be any issue with them until they were out for a few years then problems started popping up, mostly in the Southern USA, with the heat of summer (normally). Heats the fluid, not much of an oil cooler, not a lot of oil capacity, small (ish) charge pump, only one filter, they were fine in Japan where they were designed & tested, but apparently not here.
DrBT
New member
Equipment
ZD25 zero turn, M5700 Kubota tractor, Brush Bull Rotary Mower, 72" grapple
Thank You Lugbolt. You gave me something to try. Sounds like I don't want to replace the hydro with another one like it. Too bad, the machine is built like a bulldozer and the diesel runs like a clock.
one thing worth mentioning is that if you don't find any metal shavings on the screen, there's a possibility that you have a suction leak somewhere OR a possibility of a sticking relief valve or broken relief valve spring. Those would be easy fixes in comparison to replacing an HST (or both hst's)