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New holland 785 has hydraulic issue, when boom is raised to…

New holland 785 has hydraulic...
New holland 785 has hydraulic issue, when boom is raised to top of stroke it stalls the engine. You have to play with the pedals while trying to restart the engine and the boom drops slightly and then the motor will start. I have had the relief valve replaced and control valve by your left foot rebuilt and the problem still is there. It functions normally until you
Reach the top of the stroke. I am wondering if this could be electrical or hydraulic.
Thank you for reading this, I will look forward to any suggestions.
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Answered in 1 hour by:
3/10/2013
Mechanic: Curtis B., Technician replied 9 years ago
Curtis B.
Curtis B., Technician
Category: Construction and Road Equipment
Satisfied Customers: 43,988
Experience: Technican turned service manager with multiple lines of equipment and rental units.
Verified

koboma :

Does it only act up with boom, and not the bucket function??

koboma :

How did problem develop? Has it always done it or have you recently bought unit?m

koboma :

It has to be a hydraulic problem. Have cylinders been of or removed/replaced? Wondering if boom cylinder goes too far and binds, and has to be lowered before it will release pressure. The load check valve in the control valve should let cylinder hold position and not have back pressure on the engine hydraulics.

koboma :

Just affecting boom and the engine stalling when raised to top, seems to indicate the relief valve is not relieving the pressure. But with you already replacing the relief valve, that should have done it. Have any boom cylinder hoses been replaced?

koboma :

Just seems like something else is going on. The hydraulic valve just directs fluid to the cylinders, and the relief valve should relieve the pressure when maximum pressure is reached, and the load should not be there when the spool valves are in neutral position.

Customer: Thank you for your response. The problem developed after new foot control pedals and linkage were e placed, due to original ones became very rusty from deicing salts from prior owner. The person who did the work had removed the seat to do some work and it is easier to take the seat out and put back in by pushing the right hand auxiliary hydraulic hand lever to the side to get more clearance.
Customer: after the seat was put back in he started it and ran the boom lift arms up and down while the handle wuss still pushed to the right of the cab. Do you think this could be a contributing factor to the hydraulic problem?
koboma :

Do you use the auxiliary valve? Could it be partially open? Remove the linkage on the valve and be use it is centered, and test with it disconnected.

koboma :

The flow from the hydraulic pump is through the main valve, then the auxiliary valve. So it can affect the system.

Customer: Thanks for that info, it sounds simple enough to check it out. The other thing that happens when it stalls and you are trying to restart by burping the hyd. System is that there is like an electrical sounding chirp. I did not know if that was from the electrical module by the
Customer: right hand arm rest or would that have nothing to do with it
koboma :

I don;t think the electrical has anything to do with problem.

Customer: Thank you for your technical help, hopefully it will help to pinpoint the cause of the problem.
koboma :

OK, let me know. Thanks for the reply.

Curtis B.
Curtis B., Technician
Category: Construction and Road Equipment
Satisfied Customers: 43,988
Experience: Technican turned service manager with multiple lines of equipment and rental units.
Verified
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Curtis B.
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