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  1. #1
    Bronze Member
    Join Date
    Jul 2007
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    58

    Default Kubota 4wd front axle differential

    Hey,
    I was over a friends barn talking tractors, cars and equipment. We were talking 4wd axles while looking at his kubota L4330. We had noticed that the size of the front axle where the center differential would be is pretty small. The axle itself is pretty beefy for that size tractor, but it looks as if there isn't enough room in the center for a "typical size" ring and pinion. I don't own a Kubota and his only has about 100 hrs, so a parts or repair manual is not going to be bought just to answer this question. Does this (and other Kubota tractors) use just a bevel gear in the center of the axle, or is there a real small ring and pinion in there... Anyone got a parts or repair manual that shows this? Normal life is on standby till we can figure this out.
    I suggested we pull it apart to see, but that didn't go over too well.

    Joe

  2. #2
    Gold Member
    Join Date
    Jun 2007
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    433
    Location
    MD and FL
    Tractor
    Kubota BX24

    Default Re: Kubota 4wd front axle differential

    I don't have a 4330, but based on your description, I suspect it is the same as my BX24. Yes, the pinion gear drives a mini-ring-gear-like bevel. The spider gears are there too. What kubota has done is gotten rid of U-joints at the steering knuckles and replaced each with a pair of bevel gears. Bevels at each end of the axle tube turn shafts which also act as kinpins. The bottom end of these shafts turn the final large bevels, which look a lot like traditional ring gears. This is where they get the final drive gear reduction, since the one in the center of the axle is so small. Hope my explanation wasn't too confusing, I need to learn how to post pics since "...picture worth 10,000 words"...
    John

    BX24-loaded R4s/60" MMM/rear bagger/arm rests, Woods RCC42, 3PT Splitter, TuffTop, Bro-Tek skidplates/thumb/ripper, BXpanded forks/bag, American Solutions grapple, Berlon mini-toothbar, home-made ROPS lights...more to come...

  3. #3
    Platinum Member
    Join Date
    Sep 2005
    Posts
    686
    Location
    West Michigan
    Tractor
    B3030

    Default Re: Kubota 4wd front axle differential

    That is a pretty good explanation of how it works.

  4. #4
    Bronze Member
    Join Date
    Jul 2007
    Posts
    58

    Default Re: Kubota 4wd front axle differential

    Thanks for the reply guys,
    The typical bevel gear front end on CUT's I'm ok with. Had a few apart to repair over the years and the end reduction by the wheels are all about the same. It was the reduction in the center of the axle that threw us. The center ring gear on this hp size tractor is typically about 6 to 8" in diameter. The OD of the axle on the kubota at this point (center pivot point and also where the driveshaft enters) is probably about 5". Which means that if there were a typical ring gear in there it would have to be 3.5 maybe 4" at best. I didn't think the ratio of reduction at the wheels was high enough to support this. I'd love to see a parts blowup.

    Joe

  5. #5
    Veteran Member alchemysa's Avatar
    Join Date
    Oct 2006
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    1,222
    Location
    South Australia
    Tractor
    Kubota B1550HSD

    Default Re: Kubota 4wd front axle differential

    Quote Originally Posted by dogbreath108
    I'd love to see a parts blowup.
    Joe
    Asstd free parts manuals here...
    http://www.mediamax.com/kubotabooks

  6. #6
    Super Member
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    Sep 2000
    Posts
    6,514

    Default Re: Kubota 4wd front axle differential

    Remember that the center section AND the bevel gears at the wheels BOTH reduce the ratio, so you don't need one large R&P.

    jb

  7. #7
    Bronze Member
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    Jul 2007
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    58

    Default Re: Kubota 4wd front axle differential

    Thanks alchemysa for the link on the manuals. It cleared thing up!

    I downloaded the one for the L4310 which is basically the same tractor. You can see the real small center ring and pinion and the axle shape. Looks like they slip the assembled differential in from one side of the axle, and they can get away with it because it so small. It also looks like they pick up some more ratio (maybe 2:1) on the upper kingpin bevel set. This would make sense because the casting here is a bit bigger (than on other similar size machines) to fit the gear. On most other CUT tractors that I have seen and worked on, all three kingpin bevel gears are the same size (1:1 ratio) down to the ring gear behind the front wheel.

    I also downloaded the manual for a 5000 series and it shows a more typical front axle assembly that I have seen on other makes with this design. A much larger ring and pinion assembly on the differential. But still using the bevel gear front axle design. And more than one piece (casting) on the center section.

    I like the fact that on the smaller HP machine the axle center section is one piece and smaller in the middle as it helps with the ground clearance. Probably keeping it from getting bashed on unseen rocks and such..

    Well it looks like I won't be sneaking over to my friends barn and taking the 4330 apart just to see.

    Joe

  8. #8
    Gold Member
    Join Date
    Jun 2007
    Posts
    433
    Location
    MD and FL
    Tractor
    Kubota BX24

    Default Re: Kubota 4wd front axle differential

    Following up on what jb said...there are three sets of bevels in the chain, each contributing to the reduction...
    John

    BX24-loaded R4s/60" MMM/rear bagger/arm rests, Woods RCC42, 3PT Splitter, TuffTop, Bro-Tek skidplates/thumb/ripper, BXpanded forks/bag, American Solutions grapple, Berlon mini-toothbar, home-made ROPS lights...more to come...

  9. #9
    Veteran Member
    Join Date
    Sep 2004
    Posts
    2,337
    Location
    Kansas, Butler county, Just east of DooDah
    Tractor
    Kubota L4200 GSTCA

    Default Re: Kubota 4wd front axle differential

    Then add the reduction that the smaller wheel tire assembly as compared to the rear, and you will have a lot of total reduction KennyV.

  10. #10
    Elite Member
    Join Date
    Sep 2003
    Posts
    4,142
    Location
    New Brunswick, Canada
    Tractor
    Kubota L5030 HSTC, MF 5455

    Default Re: Kubota 4wd front axle differential

    Thats a pretty common question, it is also asked on planetary axles since the center section is small too. People with an auto background don't see this stuff.

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