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Diff questions

Discussion in '80-Series Tech' started by scottryana, Feb 7, 2018.

  1. HDJdreams

    HDJdreams SILVER Star

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    And drill the hub flange for 6 dowels.
     
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  2. HDJdreams

    HDJdreams SILVER Star

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    Do 4.56 gears exist for 98+ 9.5”?
     
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  3. scottryana

    scottryana

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    I only see 4.30 and 4.88 on Nitro's website, but there might be other gear manufacturers that do a 4.56. I haven't really looked since I will be using Nitro.
     
  4. HDJdreams

    HDJdreams SILVER Star

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    Planning on doing 1.1 high range transfer case gears now with stock axle ratio (I have new “34” inch BFGs) then replacing those down the road with 37s and upgrading axles. 4.56 would be perfect, 4.88s would be on the low side.
     
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  5. mryanangel

    mryanangel SILVER Star

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    I think you are running a 1HDT, and perfect gearing may be different than my perfect gearing with the 6BT, but I will give my perspective on what the best combination for me is.

    6BT + NV4500 + 1.1 Overdrive gears in HF2AV + 4.1 diff gears + 37" tires, brings my engine RPM to about 1800 at 70mph, which is perfect for the cummins motors peak operating band.
     
    Last edited: Feb 14, 2018
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  6. BILT4ME

    BILT4ME

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    So, being semi-ignorant on this......

    If I wanted to just beef my drive train a bit, I could:
    1) Buy a stock 100 series differential (4.11 gears, 32 spline pinion, 30 spline axles)
    2) Buy a replacement 32 spline flange to adapt to my driveshaft (or replace one end of my existing driveshaft to match)
    3) Buy "custom made" axle shafts for the rear full-float axle housing
    4) Drill the hubs on both sides for more dowel pins and install hardened dowels
    5) Assemble
    6) Well, it's step 6........

    Is that what you're saying? Especially if I wanted to stay with stock 4.11 gear ratio? (I know nothing about the 100 series, so this thought process is new for me on this.)
     
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  7. HDJdreams

    HDJdreams SILVER Star

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    I WISH I had a 1HDT! I am running 1FZ, but soon to be turboed:clap:

    I can really appreciate getting gearing right, especially for Cummins 5.9. I had to sell my 05 Ram because it was too noisy, especially on 80 mph freeways.
     
  8. scottryana

    scottryana

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    Correct mostly

    1) Yes OEM or aftermarket
    2) You have to buy the flange you can't adopt your driveshaft because it wouldn't have anything to bolt to without the flange
    3) Yep need 32 spline full floaters (I think JustDifferentials said they had them)
    4) You could drill for more dowels, drill for larger bolts or end at step 3 up to you.



     
  9. Box Rocket

    Box Rocket

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    Following. Interesting topic.
     
  10. scottryana

    scottryana

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    Encase anyone is wondering where the strength in the gear comes from.

    In the first picture you can see that the gear teeth are shorter to make room for the bolt circle this is the 80 gear.

    In the second picture you can see the ring gear teeth are longer, the pinion teeth are longer and the pinion spline goes from 27 - 32 spline.

    [​IMG]
    [​IMG]
     
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  11. HDJdreams

    HDJdreams SILVER Star

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    Thanks for the pictures! Obviously the 32 spline is bigger, but for us geeks out there what’s the minor diameter of the 32 spline vs 27?
     
  12. scottryana

    scottryana

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    This is kind of a WAG but I would guess 1.125" vs 1.38"

     
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  13. bwesty

    bwesty

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    Following along, good idea.
     
  14. BILT4ME

    BILT4ME

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    Ok, the next question on the list is can I buy factory locked 100 diffs and plug them into my 80 harness?

    What about enough room left in there for the locking diffs in general (ARB/Harrop)
     
  15. scottryana

    scottryana

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    That I can not answer sorry I do not know if a 100 locking rear diff will plug straight in.

    But an ARB 100 rear carrier will work and is what you need to use the 100 ring and pinion, etc.

     
  16. HDJdreams

    HDJdreams SILVER Star

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    As rare as locked 100 diffs are, it would be a lot easier (and stronger) to go for ARB/Harrop. The point of the mod is to get the strongest rear axle possible, the factory locker would be a step back.
     
  17. scottryana

    scottryana

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    Agreed

     
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  18. BILT4ME

    BILT4ME

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    Thank you both!

    Those are the answers I was looking for!
     
  19. nukegoat

    nukegoat

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    The additional tooth length perhaps does make a difference when under extreme pressure, but usually the bad breaky kind of load drives the ring and pinion away from each other which moves the mesh pattern up and out. I think. So, i mean, the 100 series gear set is stronger for sure but if the carrier itself is physically larger then thats a more significant benefit IMO. This is in @Malleus wheelhouse. I really like the idea and I think anyone running 37s or in that ballpark should seriously consider this if an option
     
  20. nukegoat

    nukegoat

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    Significantly. But remember your t case output is a hollow 30 spline