2640 hydraulic problem
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    2640 hydraulic problem

    This is my first post to the forum I've done a lot of research and can't seem to find a answer. I have talk to a few John Deere mechanics and getting different answers. I have a 1977 2640 which has the pto engage on the left side by your foot and the pto brake between the shifters. My hydraulics have stopped working unless the pto is engaged then everything works fine. With pto off I loose everything no power steering third arms won't raise nothing. Disenge the pto lever in the left and and then the pto on in between the gear shifter and everything works as it should. I was told by one mechanic rock shaft or trans pump. And. The other mechanic makes more since he said seals bad on the pto brake he said with pto brake shut it cause internal leak and loose pressure. He said when engage pto it opens another valve allowing the hydraulic to bypass the leak. He told me it wouldn't hurt to run it like this just looking to make it to winter so I can split it. I was looking to see if anybody else had this problem or any ideas about it. Thanks

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    Mar524ak's Avatar
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    What happens when tractor is idle, pto off and you press in clutch? If you loose all functions the transmission charge pump check valve is leaking or defective. Itís allowing oil in aux. reservoir and charge line to main pump to leak back to sump through the transmission pump. To me itís a internal leak in the hydraulic charge circuit.


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    Welcome to GTT
    1st let me clarify the operation of the independent hyd pto on your tractor. The lever by operators left heel when seated is merely a disconnect lever between pto frt drive shaft & rear output shaft. Control knob between gearshift lever when raised up engages pto clutch/disengages pto brake & when in down position engages pto brake/disengages pto clutch. I agree with mechanic that stated there's a leak in pto brake circuit. JD tractors of this era have a long history of failed supply tubes or tube sealing rings in this area. You could remove top shift cover & apply compressed air to tube openings to verify leak. I suggest with 3 pt raised,engine running at operating temp look inside hyd filler hole for moving oil. This test isn't related to internal pto leak but is just another place that has a history of internal hyd leaks. Does your tractor have a FEL?

    PS: I served as a JD dealer service manager for 13 yrs when your tractor was NEW & after.

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    Quote Originally Posted by Mar524ak View Post
    What happens when tractor is idle, pto off and you press in clutch? If you loose all functions the transmission charge pump check valve is leaking or defective. It’s allowing oil in aux. reservoir and charge line to main pump to leak back to sump through the transmission pump. To me it’s a internal leak in the hydraulic charge circuit.


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    I thought tractors with hyd ind pto the trans pump operates continuously when engine is operating because it's driven from pressure plate not traction clutch. But it's been a long time since I've read a JD 40 series utilty tractor tech manual.
    Last edited by Tx Jim; 10-05-2017 at 07:34 AM.

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    I'll bet a failed oil hard line from the PTO valve to the PTO brake, causing a "leak to sump" and the transmission pump can not keep up with the leak and supply enough oil to the front pump.

    I would remove the cover from over the shifters and put a pressure gauge on the "brake" test port. With the PTO lever between the shifters in the "off" position you should have pressure at the brake port.

    It will take a split if the hard line is broken. I would also replace the PTO clutch hard line too.
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    Quote Originally Posted by Mar524ak View Post
    What happens when tractor is idle, pto off and you press in clutch? If you loose all functions the transmission charge pump check valve is leaking or defective. Itís allowing oil in aux. reservoir and charge line to main pump to leak back to sump through the transmission pump. To me itís a internal leak in the hydraulic charge circuit.


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    With pto I have no hydraulics no power steering third arms won't raise nothing

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    Mar524ak's Avatar
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    You got internal leaks somewhere. If I had it I would do a flow test and pressure test. Probably replace hard lines and pump. Depends what all you find if you get in there and do tests.


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    Quote Originally Posted by Tx Jim View Post
    Welcome to GTT
    1st let me clarify the operation of the independent hyd pto on your tractor. The lever by operators left heel when seated is merely a disconnect lever between pto frt drive shaft & rear output shaft. Control knob between gearshift lever when raised up engages pto clutch/disengages pto brake & when in down position engages pto brake/disengages pto clutch. I agree with mechanic that stated there's a leak in pto brake circuit. JD tractors of this era have a long history of failed supply tubes or tube sealing rings in this area. You could remove top shift cover & apply compressed air to tube openings to verify leak. I suggest with 3 pt raised,engine running at operating temp look inside hyd filler hole for moving oil. This test isn't related to internal pto leak but is just another place that has a history of internal hyd leaks. Does your tractor have a FEL?

    PS: I served as a JD dealer service manager for 13 yrs when your tractor was NEW & after.
    No my tractor doesn't have a FEL. Checkin the hyd filler hole. Is this to check for seals bad on the rock shaft? And will it hurt if I run my tractor like this until winter when I would be able to split it? Thanks for response

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    Quote Originally Posted by Mar524ak View Post
    You got internal leaks somewhere. If I had it I would do a flow test and pressure test. Probably replace hard lines and pump. Depends what all you find if you get in there and do tests.


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    With the pto lever on the side of and the lever in the middle engaged the pto shaft does not spin. But if I have it like this everything works as it should tractor runs fine. When I engage the pto and I bypassing the leak somehow to allow the hydraulics to run properly?

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    Quote Originally Posted by davidraley18 View Post
    No my tractor doesn't have a FEL. Checkin the hyd filler hole. Is this to check for seals bad on the rock shaft? And will it hurt if I run my tractor like this until winter when I would be able to split it? Thanks for response

    Yes you can operate tractor until you get time to repair internal hyd leak. Yes looking in hyd filler hole for moving oil is to determine "IF" rockshaft control valve seals are leaking.

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