RTV900 '06 - No Power to Wheels

Hi All,
New to the forum..and looking for help

We have a '06 RTV900.
One morning, started it up and no power to the wheels.

* We measure 0psi at the Check and High Pressure Relief
Valve (machine started in neutral)
* So no drive to the Assist or Stationary Motors.
* Hence we focus on the control of the Variable Swashplate (HST Pump)
* No problem with Regulator Valve Assembly
(Feedback Level, Control Level, Regulator Spool)
* Pressure by Charge Pump at the Charge Relief Valve is good
- reading 87psi
* Suspect the servo piston position is not changing, regardless of
Feedback Lever position, so the pump's variable swashplate remains
neutral - hence 0psi
* To verify this, we adjusted the Piston Adjusting Screw to force the
piston to move. Sure enough, we get power

Why would this need to be adjusted?
Could it indicate issues e.g. piston seals

Just not sure how to interpret the results of our "debugging"!
Any advice is greatly appreciated.

Hi and welcome to Net Tractor Talk.
Interesting issue. So after adjusting the piston you had power to the wheels and all ran as usual? Any idea when fluids were last changed and what fluids were used?

Thanks for welcome Doc.

It is a strange problem.
I've done a lot of googling over the past few days and haven't come across anything like it.

Fluids were checked by local mechanic when the machine was bought ..so there should be no problem there.
And yes, it runs fine in Low, High & Reverse once the Piston Adjusting Screw is adjusted to offset the Servo Piston.
I didn't want to test it too much, as I'm a little bit concerned of doing damage ...given that I don't fully understand why it works!

From what I've read on Kubota's product like over the years, one thing I have not experimented with is the hydro fluids. Kubota fluids only. So if it was a Kubota dealership that changed and checked the fluids lsst, I presume you would be A-OK. However, if there is any doubt about what hydraulic fluid is in your RTV I would suggest doing a fluid change and go with the Super UDT from Kubota. I would also recommend Kubota filters be used.

I have no affiliation with Kubota of any kind. This is from stories I have read by other users that have had issues when using something other than Kubota. And these issues were much like yours.

Hope this helps.

I fully agree ...I am quiet particular when it comes to the quality of fluids or consumables in any of our machinery, so I'm sure that only Kubota oil was used, from the dealer where the machine was purchased.
The local mechanic only verified the levels.

I'll continue to research it, and if I do find a solution, I'll be sure to post so as to maybe help someone else in the same situation.
I appreciate your input Doc!