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  1. #1

    Default JD 790 Front Axel

    I have a problem with my 790 that I am hoping maybe someone could help at least point me in the right direction. I have been doing a lot of digging with the bucket in loose sand so I have kept it in 4wd. Yesterday I took it out of 4wd and there was a clunking noise every few feet from the front axle. When I put it back in 4wd the clunking goes away and the 4wd works. Anyone have any ideas what it could be? Or does anyone have a drawing of the front axle I could use if I decided to take it a part. Thanks

  2. #2
    Advertiser kennyd's Avatar
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    Default Re: JD 790 Front Axel

    Quote Originally Posted by berkompt View Post
    I have a problem with my 790 that I am hoping maybe someone could help at least point me in the right direction. I have been doing a lot of digging with the bucket in loose sand so I have kept it in 4wd. Yesterday I took it out of 4wd and there was a clunking noise every few feet from the front axle. When I put it back in 4wd the clunking goes away and the 4wd works. Anyone have any ideas what it could be? Or does anyone have a drawing of the front axle I could use if I decided to take it a part. Thanks
    Welcome to TBN

    The diagram for the axle is available for free if you register at www.jdparts.com
    Not sure what the clunking is-but I would not not it go to long before you figure it out!
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  3. #3
    Platinum Member
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    Mahindra 2516

    Default Re: JD 790 Front Axel

    Don't shoot the messenger but my co-worker has has his front end re-built 3 times for the same issue. I have also heard of other people having front end issues but that is the only complaint I hear about the 790.

    Good luck and keep us informed on what it turns out to be and how it was fixed.

  4. #4

    Default Re: JD 790 Front Axel

    Thanks for the help! I really hope it is not the front gears but I fear it is. The only odd thing is it only makes the noise in 2wd. I have registered on JDparts.com and I have looked all over. Where do I find the drawings? Thanks again.

  5. #5
    Platinum Member JD755's Avatar
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    John Deere 755 purchased new in 1993

    Default Re: JD 790 Front Axel

    Quote Originally Posted by berkompt View Post
    Thanks for the help! I really hope it is not the front gears but I fear it is. The only odd thing is it only makes the noise in 2wd. I have registered on JDparts.com and I have looked all over. Where do I find the drawings? Thanks again.
    On the left side of the page click on John Deere Parts Catalog, just below Start Searching Here!.
    JD 755, 70 Loader, 60 inch MMM, Landpride rear blade, Modern box blade, Wallace subsoiler

  6. #6
    Super Star Member RoyJackson's Avatar
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    Default Re: JD 790 Front Axel

    The 790's front axle is pretty strong but it is designed to be strongest when pulling in a forward direction. Pulling in reverse reveals it's limitations.
    There were a few posts concerning front axle gears failure on TBN about 3-5 years ago. Seemed like a real rash of them for a while.
    If berkompt has been doing heavy pulling in reverse gear, he may have broken a tooth off the spur gears in the front axle.
    However, before pulling the axle, have someone observe the tractor (as close as possible) while operating in 1st gear low and reverse low. This is to try to determine exactly where the clunking noise is coming from. The tractor will be moving about 1 MPH.
    Roy Jackson

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  7. #7

    Default Re: JD 790 Front Axel

    Quote Originally Posted by RoyJackson View Post
    The 790's front axle is pretty strong but it is designed to be strongest when pulling in a forward direction. Pulling in reverse reveals it's limitations.
    There were a few posts concerning front axle gears failure on TBN about 3-5 years ago. Seemed like a real rash of them for a while.
    If berkompt has been doing heavy pulling in reverse gear, he may have broken a tooth off the spur gears in the front axle.
    However, before pulling the axle, have someone observe the tractor (as close as possible) while operating in 1st gear low and reverse low. This is to try to determine exactly where the clunking noise is coming from. The tractor will be moving about 1 MPH.
    I was actually going in reverse up a very steep grade with full bucket before the noise started happening. The thing I can't figure out is it only makes the clunk going forward and in 2wd. If it did break a spur gear is it hard to fix? I have worked on many cars before. Is it fairly straight forward? Will I need any special tools or press or anything? Thanks again for all the help! Travis

  8. #8
    Super Star Member RoyJackson's Avatar
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    Default Re: JD 790 Front Axel

    The first thing you'll want to do is buy the service manual for your 790. Make sure you get the correct one...there's been two or three (mine is actually for a 670, but there is addendums for the 790...I really need a newer manual). Your dealer can get you the correct manual if you provide the tractor's serial number (it's on a plate above your PTO guard).
    Once you review the work involved, you can decide if you want to get into pulling the axle. I understand it's about $1500 or so if you take it to a dealer. I have no idea how much is for parts and how much for labor.
    Roy Jackson

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  9. #9
    Platinum Member
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    Default Re: JD 790 Front Axel

    Be sure to check wheel lugs. Sometimes a loose wheel can make noise when not under load in 2wd.

  10. #10
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    Default Re: JD 790 Front Axel

    Its possible the noise only happens in 2wd because the gear teeth aren't under load so they have lots of play and can bang around. While in 4wd they are loaded and have less give to them to make noise.

    I imagine there is a king pin in the wheel assemblies. They are generally difficult to get out. If its a spider gear, the real difficulty is getting to the axle to replace them. The spider gears themselves are pretty easy to change out. The ring and pinion requires some know-how and specialty tools to setup properly for maximum strength and life.

    I can't imagine if you lost a tooth on any of those gears that your axle won't lock up at some point from the tooth getting wedged somewhere but anything is possible.

    Roy, when you say the reverse is weaker than the forward, do you mean because running the ring gear on the coast side of the teeth is inherently 20% or so weaker than running the drive side or is there some other design feature that makes it weaker?
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