7700 tractor, hydraulic problem when cold starting
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    7700 tractor, hydraulic problem when cold starting

    Hello! I have just joint the forum.

    The problem is this: you start the tractor in the morning and the main hydraulics (i.e. the steer) work for five seconds. Then, you can heard a little sound at your back and the steer can´t move. In this conditions, the 4 powershift gears (the tractor has a Quad Range trans) work fine and also the PTO runs. The rest of hydraulics stay dead. In order to "resurrect" the sytem, you have to step hard the throttle: again, you can heard a sound at your back and the tractor will work properly all the day.

    Remarks:

    - The colder is the temperature, the harder you must step the throttle.

    - It has new hydraulic fluid, new hydraulic filters, and we cleaned the screen (it doesn´t have metallic chips)

    - The tractor has not oil leaks. All stuff are dry and clean.



    Thanks in advance.

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    Welcome to GTT
    May I ask what country you reside in?? My knowledge of JD closed center hyd systems ended with the 50 series when I left JD dealership. My guess is there's a problem with one of the hyd charge circuits. Maybe one of the more knowledgeable members will reply. At least you've already changed hyd oil,filters & cleaned screen which is an excellent diagnostics starting point.
    Last edited by Tx Jim; 11-23-2019 at 07:54 AM.

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    Quote Originally Posted by Tx Jim View Post
    Welcome to GTT
    May I ask what country you reside in?? My knowledge of JD closed center hyd systems ended with the 50 series when I left JD dealership. My guess is there's a problem with one of the hyd charge circuits. Maybe one of the more knowledgeable members will reply. At least you've already changed hyd oil,filters & cleaned screen which is an excellent diagnostics starting point.
    ==========================================

    Thank you for your kind answer. I'm from Spain. I agree with you, the problem must be that a pipeline lose oil when the tractor is stopped.

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    I sent you a PM with a JD technician's contact info.
    HTH's,Jim

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    Don_Quixote (11-24-2019)

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    Don, I suspect you may have a suction leak under the charge pump. The charge pump sits on top of rear differential housing and the hydraulic pump sits on top of it. The suction port seals with a gasket that may be bad. Check out item #6 in diagram. If there is a leak there, it would allow oil to drain back to sump when tractor sits between uses. It will then be hard for pump to pull oil back up since it will also be sucking air.
    Attached Thumbnails Attached Thumbnails 7700 charge pump.PNG  

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    Don_Quixote (11-24-2019)

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    Unfortunately I don't have any info to help you. Just wanted to say welcome to GTT, and awesome username!

    Don Quixote is one of the best novels ever written IMO.

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    Don_Quixote (11-24-2019)

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    Quote Originally Posted by Tx Jim View Post
    I sent you a PM with a JD technician's contact info.
    HTH's,Jim
    Many thanks!

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    Quote Originally Posted by JROC View Post
    Unfortunately I don't have any info to help you. Just wanted to say welcome to GTT, and awesome username!

    Don Quixote is one of the best novels ever written IMO.
    The novel take place in our land. I agree with you: it´s a great novel. Thanks for your kind message!

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    jd110 (11-27-2019)

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    Quote Originally Posted by jd110 View Post
    Don, I suspect you may have a suction leak under the charge pump. The charge pump sits on top of rear differential housing and the hydraulic pump sits on top of it. The suction port seals with a gasket that may be bad. Check out item #6 in diagram. If there is a leak there, it would allow oil to drain back to sump when tractor sits between uses. It will then be hard for pump to pull oil back up since it will also be sucking air.
    It´s a clever diagnostic. I thought that the main pump (pistons) is fed by the gear pump located in the front end of the gear box.

    It was not logic for me that the PTO and the powershift gears run, while the rest of hydraulic devices did not. Now, I can see the reason. Many thanks!

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