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Thread: JD 6630 Premium Back end pressure / leak

  1. #1
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    JD 6630 Premium Back end pressure / leak

    Hi, new user here so sorry if I get something wrong on the site!

    I have a 2007 6630 Premium 6000 hours. Just stopped it from 10 mins work and could hear a hissing from the back end. Worked out when I unscrewed the hydraulic oil filler cap it released a huge amount of air. At the same time there was an oil leak from the main casing around the pto (not from within the pto shaft housing). The oil in the glass window was also frothy / cloudy. Any ideas what it could be? Many thanks

  2. #2
    Senior Member Footsfitter's Avatar
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    Re: JD 6630 Premium Back end pressure / leak

    Quote Originally Posted by Combeland View Post
    Hi, new user here so sorry if I get something wrong on the site!

    I have a 2007 6630 Premium 6000 hours. Just stopped it from 10 mins work and could hear a hissing from the back end. Worked out when I unscrewed the hydraulic oil filler cap it released a huge amount of air. At the same time there was an oil leak from the main casing around the pto (not from within the pto shaft housing). The oil in the glass window was also frothy / cloudy. Any ideas what it could be? Many thanks

    Welcome to the forum.


    Bit of a coincidence but I've been trying diagnose a hydraulic problem on a NH TM155 recently and one test is to determine if the system is sucking in air somewhere, on the TM its pretty simple as you remove the breather hose of of the top cover and replace it with a length of clear pvc hose into which you pour enough back end oil to make a slug of oil that sits in the bottom if you make the hose into a U bend. then with the engine running at about 1200rpm you watch to see what happens.

    An external leak may allow air into the pump/suction side of the system which is expelled into the back end. The slug of oil in the tube will show bubbles exiting or in a serious problem blow the oil completely out.

    The TM system vents to air, but I'm not a JD person so not sure about your setup but if you can rig up a sight tube and see if it bubbles out air readily then i'd look at if its sucking air in to where the oil is leaking out of the main casing? The other option could be a leaking seal/oring on the suction tube/gallery inside feeding the pump especially if its located above the oil level and able to suck in air?

    Also check for a breather to see if there is a valve there thats stuck or a pinched hose? Some makes/systems may have a fair pressure held in by a sprung loaded cap/breather but usually it will only be a few psi. The frothy oil, if excessive may point to sucking in oil or even a blocked/restricted suction filter/screen.

    Lots of things and what-ifs to consider and check.
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  3. #3
    Senior Member T P's Avatar
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    Re: JD 6630 Premium Back end pressure / leak

    I once had a problem with frothy oil on a 40 series ford that turned out to be a defective filter vacuum switch. The switch that warns you when the pump is sucking hard on a blocked filter which then illuminates the filter blocked warning symbol on the dashboard. Most tractors have a similar switch on backend filters which utilises an internal diaphragm to pull against a spring and close a set of contacts. After thousands of hours of tension and heat the diaphragm can puncture letting the pump(s) access a small but continuous stream of air which is duly compressed by hundreds of psi and heated before frothing the oil as it drops back to atmospheric pressure on being returned to the backend. The froth created soon starts to be sucked for oil and the situation spirals out of control. It wasnít a complex fault but it caused a lot of havoc and damage as the effect seemed to be to create a lot of heat which hardened all the seals and o rings the oil ame into contact with. The tractor was a never ending source of new leaks thereafter until most seals had been replaced. So Iíd say look for potential leaks on the suction side of the pumps assuming the filters are clean. I think the 20 Deereís might have had a large suction gauze that pulled out of the lhs just in front of the puh when a hex bung was unscrewed,I donít know if itís on the 30ís never worked at one.I had the diff out of a 6520 for repairs a lot of years back and I think I recall it from then but I could be wrong.

  4. #4
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    Re: JD 6630 Premium Back end pressure / leak

    I'd looking at transmission breather first 🤔

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