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Valmet 860.3 brake issue

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Valmet 860.3 brake issue

emanuelmelodesousa  
#653994 Hello friends,

I have a Valmet 860.3 with a brake problem, i would like to know if everyone ever experienced this situation:

When the machine goes downhill loaded, if we release gas the pedal the machine dont stop (even lights at maxi stays off), only if i active work revs or press brake pedal the machine actives the work brake. If we go uphill we dont have the issue.

What we have done: Speed sensor is checked and good, gas pedal was calibrated, vbu was loaded again, transmission pressures checked (forward and reverse).

Looks like that the speed sensor is still detecting movement (when going downhill) and might be the reason for not stoping.

Thankx in advance.

Regards 💪



   TS
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Re: Valmet 860.3 brake issue

AKKAMAAN  
#654069 Sounds like the hydrostatic system is over-running ie the machine body pushes the hydrostatic motor to act like a pump and that way it starts turning the hydrostatic pump like it is a motor that then starts revving up the engine rpm. And that makes it an evil circle and thee machine goes faster and faster without control except for the "emergency" travel foot brake system. Usually, there is a knob (variable potentiometer/resistor)that sets a cap on max speed. It is a common trick to turn that potentiometer down and that way limits the max speed.
The hydrostatic system has a variable reversible pump and a variable hydraulic motor. The speed increase starts with a pilot prséssure that makes the pump increasing the swashplate angle to its max position. When we demand even higher speed the hydrostatic motor starts decreasing its "swashplate" angle by further increasing the pilot pressure. The potentiometer sets a cap on max pilot pressure so the hydrostatic motor can't decrease its displacement. If this doesn't help turn down the potentiometer even more to limit the pump displacement.
Under normal conditions, the electronic control system should be able to control the speed governed by the engine rpm sensor, but when heavily loaded I steep terrain it's often needed to do the potentiometer trick...

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Re: Valmet 860.3 brake issue

emanuelmelodesousa  
#663208 Hello AKKAMAAN.

Thank you for your reply. The solution was a new hidrostatic pump, fixe the problem :)

Thank you.

   TS
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