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JD400 backhoe blowing hydrualic pump oil seals.

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Hebridian

08-30-2002 01:04:39




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I have a JD400 Backhoe, I beleibve it was manufactured in Germany and was first registered in the UK in 1975.
When I purchased the unit , it had a small leak from the shaft of the pump. I have had the pump re-built and when it was fitted I was able to raise the front bucket fine3, but as soon as I tried to move the rear arm, the oil seal on the pump shaft blew (totally). I have since had the pump rebuilt again and exactly the same thing happened. We are trying to get some manuals and diagrams on the hydraulic system but at present we are working blind. Anyone have any ideas what is wrong and where ? John Deere are being as hepful as possible but are quoting 6 weeks for the manuals.

Thanks in advance

Hebridian
Kent, England

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G-MAN

08-30-2002 07:44:42




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 Re: JD400 backhoe blowing hydrualic pump oil seals. in reply to Hebridian, 08-30-2002 01:04:39  
Cannonball is right about the bleed line, and it will be the easiest thing to check. I've also seen a JD hydraulic pump that kept blowing the seal out because there was a very small crack leading from one of the pumping cylinders to the inside of the case. Under high pressure, it was leaking fast enough that the case drain couldn't keep up and it would blow the seal. The bad part was that I pulled the pump and disassembled it two or three times before I finally went over it with a fine toothed comb and saw the crack. A new pump cured the problem.

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hebridian

09-04-2002 01:58:40




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 Re: Re: JD400 backhoe blowing hydrualic pump oil seals. in reply to G-MAN, 08-30-2002 07:44:42  
Thanks for the feed back gentlemen.
I have tried this with 2 different pumps, both have been rebuilt, so I would be suprised if it was the pump (but I will check) It also seems that when the pump is fitted, I raise the front bucket and all is OK, it is only when I try to move the backhoe, the seal blows.
On what I beleive if the fluid resevoir, under the nut, there was a ball bearing held by 2 pieces of sprung metal. This now seems to have dissapeared. Could this have gotten in to the lines ? The engineer working on the machine says this is not likely. What was the ball bearing for ? We are trying to get manuals from JD but in the mean time any feedback is really appreciated!

Hebridian

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G-MAN

09-04-2002 09:45:21




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 Re: Re: Re: JD400 backhoe blowing hydrualic pump oil seals. in reply to hebridian, 09-04-2002 01:58:40  
I can't help you much anymore at this point, as I don't have a parts book to look at what you're describing. However, if there was something there before that isn't now, and the onset of the problems coincides with the disappearance of that part, there's a good chance that had something to do with that. I recommend finding a service manual and doing whatever troubleshooting is given in the book, as that is generally the best method for tracking down hydraulic problems - a step by step evaluation.

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cannonball

08-30-2002 05:01:50




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 Re: JD400 backhoe blowing hydrualic pump oil seals. in reply to Hebridian, 08-30-2002 01:04:39  
you need to make sure the small line that comes off pump is not stoppped up...if not then your shaft has to have too much wear and allowing too much hyd fluid to come into cavity behind seal and small line can not flow enough...have nice day may god bless



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