John Deere 955 rolls freely when foot removed from hydro pedal

[kimodc]

Hello,
I am slowly going through and rebuilding a john deere 955... I got it running and driving good, but occasionally, when I remove my foot from the hydro pedal, it freely rolls for a bit instead of the hydrostatic system automatically "braking".
This is happening whenever I am reversing and I say occasionally because it is not consistent and varies as to how much it will free travel. The higher rpm seem to make it worse. When I am travelling forward and release the pedal, the system automatically brakes as it should to the point of sliding the rear wheels. Any ideas what might be causing this? The eccentric adjusting bolt it adjusted correctly, the neutral return rollers and spring are all working correctly. It seems like it might be something inside the hydrostatic pump that may be causing this. Any one else experienced this?

 

[pmsmechanic]

Is the pump sucking air? Is there enough transmission oil? Is the free wheeling worse after the tractor is warmed up? Or just the opposite?

 

[Sysop]

+1 ^^^

Air is compressible and any foaming in the hydrofluid will cause similar to what you describe. Heat generally brings out the worst in HSTs, as suggested above (after checking fluid levels) heat it up and see if there are any differences in the operation.

 

[kimodc]

Thanks for the responses....The fluid level is fine. I have not run it long enough to heat the oil up, hopefully this weekend I will get a chance. If it was something with the hydro fluid, I would think it would act up equally in forward and reverse, but it only happens in reverse, making me think it might be something more with the transmission pump itself. I will give it a good run this weekend and see how it reacts.

 

[pmsmechanic]

The forward/reverse pedals are connected to a rod that operates a lever on the side of the transmission. On my 955 the forward/reverse shaft that goes into the transmission had a bushing that was worn out causing leakage and some slop. That is another area that might be worth looking into.

 

[kimodc]

The shaft that goes into the transmission had a little slop in the bushing, but jd recommends replacing when the yellow coating of that bushing wears down to the point of the brass showing through...mine was just starting to show a little brass, but at over $300, I figured I could wait a little.

BUT..... I did find the cause of the problem, my neutral return spring was not tight enough to spring the pedal back as fast as it should, so tightening that up has the tractor coming to an abrupt stop in forward and reverse. I guess the way my hydro pedal shafts are worn, they need a little more pressure to return from reverse. So that is all good and I thank you for your suggestions.