[Tyler Leachman]

Hello,
I recently picked up a well used f935 front mower, did a filter and fresh fluid on transmission unit and it seems to function ok but having an issue with ground speed, it seems rather slow until I lift the deck and hold it in the lift position and stall the lift rams, it speeds up to what I suspect is normal full speed. I have not yet had a chance to get a hydraulic schematic. Anyone have similar issue and an ideas?

 

[HarveyW]

Howdy Tyler,
We have had this issue with an f935 mower before. Turned out to be loose linkage. Click on the attached link:

https://www.tractorforum.com/threads/please-help-deere-f935-very-slow-ground-speed-problem.30087/

 

[Tyler Leachman]

Thanks for the reply HarveyW,
The linkage is in poor shape for sure and defiantly an issue I will have to address, I’ll check out that link you provided, thanks, but it did seem odd that with pedal full foreward that ground speed would increase once I lifted deck and stalled out the rams and decrease again once I let the deck lift go back to neutral position, as if I’m loosing flow through the deck lift valve that should be going to the hydrostatic drive if that’s possible.

 

[HarveyW]

Tyler, when you raise the deck, does it stay up or drift down? Maybe you have leakage through the lift cylinders, or maybe your lift control valve is bypassing fluid?? This would take away from your hydrostat performance.

 

[Groo]

That would take a monstrous amount of valve leakage to impact drive motor speed.
Is it possible a previous owner.put an open center spool when it should have been a closed center spool?

A more likely possibility would be something off with the load sense system and it requiring more pressure to shift the pumps swash plate than it should?

I really don't have much knowledge on these types of systems, so just guessing.