Hydraulics on John Deere 780

cp57 · Nov 9, 2016

John Deere 780 Windrower - Question on hydraulics when cold platform raises up and down fine. After warming up platform will not raise but reel rises up and down fine. Any answers.

Bob · Nov 9, 2016

Pump is worn out. Pump was used as a belt tightener/idler for the platform drive, and got tugged on pretty hard by the belts, while simply having a bushing at the drive end. Bushing wears, shaft moves off center, gears cut into aluminum pump housing, making for a infatuation where warm, thin oil can sneak past, making pump useless and non-repairable.

cp57 · Nov 10, 2016

(quoted from post at 23:49:54 11/09/16) Pump is worn out. Pump was used as a belt tightener/idler for the platform drive, and got tugged on pretty hard by the belts, while simply having a bushing at the drive end. Bushing wears, shaft moves off center, gears cut into aluminum pump housing, making for a infatuation where warm, thin oil can sneak past, making pump useless and non-repairable.

Is it possible that the hydraulic oil is leaking by the control valve that raises the platform?

Bob · Nov 10, 2016

While is suppose that's a (slim) possibility, I still think most likely it is a worn pump. The platform lift cylinders are not very big in diameter, and it takes a LOT of pressure to lift the head, vs. the reel.

To determine for sure if it's the pump, one would connect a flo-rater between the pump and the valve and load the pump with the flo-rater and note if it can put out the required pressure and flow.

I don't have that info at hand, obviously would be in the service manual (might have to check with a friendly dealership shop foreman) or possibly at least the pressure info MAY be in the operator's manual.

Hydraulics on John Deere 780

cp57

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Bob

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