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Fron disc convesion nearly done gear question

Discussion in '40- & 55-Series Tech' started by FJ55partsBoise, Dec 1, 2003.

  1. FJ55partsBoise

    FJ55partsBoise

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    Ok I think I messed up my disc conversion. I took the front axles from a 78 FJ55 with all disk parts and placed them on the 1974 ( made in 1973) FJ40 I have. Just so we are clear it was an axle out conversion. I am 95% done and I read this:

    78+ fj55's have 3.70 gears I believe. For the most part 55's follow the same changes as a fj40. PS and AC were both options on late model 55's, aftermarket(dealer installed) AC on earlier 55's. Hood changed in.....78 I think, its higher.

    The concerning part is the 3.70 gear comment. Did I screw up? I pulled the fine spline axles and swapped them into the 1974 pumpkin that never left the cruisers. I did just a typical knuckle rebuild from there? I thought I was matching 4.11 gears?

    Will this thing roll or did I screw up with mismatched gears?

    Thanks
     
  2. cruiser_guy

    cruiser_guy

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    Aaron,
    If you did not change the third members/axle housing then your gearing is just fine. If you changed the third member then you'll need to check out what you have at each end.
     
  3. fsusteve

    fsusteve

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    Aren't the spline counts different between 74 and 78's?
     
  4. cruiseroutfit

    cruiseroutfit Supporting Vendor Moderator

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    [quote author=fsusteve link=board=1;threadid=8271;start=msg69929#msg69929 date=1070330773]
    Aren't the spline counts different between 74 and 78's?
    [/quote]

    Only on the birf end.. the diff ends are all 30 spl. 1.31" shaft (69'+)
     
  5. FJ55partsBoise

    FJ55partsBoise

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    Front disc conversion nearly done gear question

    OK- I did not change the third member and the fine spline inner end fit into the third member perfectly when I did the conversion.

    So how does 3.70 and 4.11 gearing vary then? By the third member alone? I guess I don't get how the 78' FJ55 are 3.70 and the 74' FJ40 are 4.11 right?

    How do they vary?

    thanks
     
  6. Big_Moose

    Big_Moose

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    The ring & pinion dictate the differential gear ratio.

    A diff w/4.11 has a 37 tooth ring gear & a 9 tooth pinion -> 37/9=4.11111111111111111
    A diff w/3.70 has a 37 tooth ring gear & a 10 tooth pinion -> 37/10 = 3.7

    Toyota change the differential gear ratios in response to market changes, product competition, and gas mileage issues of the 70's
     
  7. hammerhead

    hammerhead

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    3.70 and 4.11 are the ratios of the ring and pinion gears. They are in the third member which, it seems, you left in the rig with the axle housing. If you didn't mess with the pumpkin you have nothing to worry about.