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3.7's, 4.11's and coarse to fine changeover

Discussion in '40- & 55-Series Tech' started by cult45, Oct 11, 2017.

  1. cult45

    cult45 SILVER Star

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    Trying to find a bolt in 3.70 for a disc brake/FF rear axle conversion I'm doing. All factory 40 series parts.

    Can anyone tell me the following (with respect to 1975 and under trucks):

    Was the 3.70 ever a fine spline?
    If so, what month/year did 3.70's go from coarse spline to fine spline?
    Can you utilise the original 3.70 centre and housing and add factory 40 series disc brakes as a bolt on proposition?

    Apparently the last of the 3.70 equipped trucks had a fine spline front centre (diff side only). Which would be perfect!

    Also apparently you can use the original housing if you grind out the ball a little.

    Cheers,

    Dan
     
  2. Living in the Past

    Living in the Past SILVER Star

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    I'm confused. 3.70:1 diffs would very hard to find prior to 1/79. From 1/79 on side gears and pinions we're all fine spline. US market 1/79 to 8/87 all Land Cruisers imported to the US were 3.70:1. A few early sixties FJ40 made it to the US with higher than 4.10:1 gears. Those were coarse side gears and pinion.
     
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  3. cult45

    cult45 SILVER Star

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    I was hoping you or one of the other knowledgable folk would chime in :)

    Our situation is the opposite. Almost all 40's until ?/1971/2/3 were sold with 3.70's, almost all 40's after ?/1971/2/3 were fitted with 4.11's. The only exception being FJ62 autos which were fitted with 3.70's. So the bulk of centres in Aus are 4.11's. I did hear the last of the 3.70 fitted trucks, in the early seventies, in the front centre only, had fine splines and therefore could be bolted into a standard 40 series disc front housing that would have originally carried a 4.11. In addition, the same centre could also be fitted to a standard FF housing.

    My aim is to take a pair of 1984 housings [disc front, single cylinder rear with handbrake rear axle] and whilst they're torn down for a rebuild install 3.70 centres. I realise you can probably bolt a 10 tooth pinion into a 4.11 centre but that would require sending it all off to a diff shop for fine tuning, and if only the front is fine spline like legend has it - then the centre should be low mileage and in good order.
     
  4. nogo

    nogo

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  5. Living in the Past

    Living in the Past SILVER Star

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    Sorry my mistake should have know that. Use my phone most the time and location doesn't show up when it's vertical. US is probably you best best to find some. If I can help let me know. Just ring and pinion sets could be mail.

    That is interesting about the FJ62. Those were 4.10:1, all were automatic here.
     
  6. 65swb45

    65swb45 Supporting Vendor

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    Ditto what LITP wrote. I knew a lot of stuff in AU was different than here, but I never would have suspected the diffs to be one of them.

    Here, the driveshaft flange pattern was the same from 74-84, coarse or fine spline, so swapping 3rds is plug and play.
     
  7. cult45

    cult45 SILVER Star

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    Thanks fellas, that's kind. I'll keep up the hunt here as I know a few lads with some 3.70's - they're a helluva a drive and still in housings though.

    This is what I use. Hope it's right!

    comp_flange.jpg
     
  8. Living in the Past

    Living in the Past SILVER Star

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    I see 10 spline and 27 spline listed for pinion on the diffs. What was the spline count for the brake drum on the transfer case over the years. Have one that was given to me a long time ago that is 16 spline. What would that be from? Person who gave it to me said it wouldn't fine any of the one piece cases. Curious is this from the split case?
     
  9. cult45

    cult45 SILVER Star

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    Sorry mate I've probably confused you. I use that as a general aide when discussing third members. My original question is about axle splinage. According to my information, the last of the 3.70's ran a fine spline on the inner end of the front axle and coarse on the FWH end.
     
  10. lcwizard

    lcwizard Supporting Vendor

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    @cult45 Everything after 1968, shipped to the USA, was a fine spline inner on the axle shaft. Only the 4:11 ( 37/9 tooth ) was available until the end of the 70's. In the 80's 3:70 was the standard until 88 when the FJ62 was introduced. The gearsets at that point were 4:10
    ( 41/10 ). The pinion shaft was 10 spline until the 3:70 sets were introduced after that it was all 27 spline.
    Our axles were fine spline inners and coarse spline outers in the early 70's. when disc brakes came in 76 the birfields were changed from coarse to fine. The first three years of fine birfields were slightly longer.
    When Toyota added factory locking Aisin hubs , sometime in and or around 79, the birfield was shortened. That birfield design carried over to the remaining years of 40, 60 and solid axle trucks.
    In the US you can mix and match coarse outers to fine inners however I believe coarse birfs are no longer available here so you're stuck with used parts. Here, the stock axle shafts, after '68 are all 27 spline at the birfield so popping off one and swapping to another is simple. We swap birfields to do disc brake conversions on a regular basis, retaining the old shafts
     
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  11. Living in the Past

    Living in the Past SILVER Star

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    I always get confused with the 4.10 and 4.11 which is which. Have one 80 series E-locker and know mixed with a early diff would be off.
    SOR show 1/78 as the switch to fine spline pinion. Have seen a date later in 78 on Mud as well. Confused we're there 78s that were 4.11:1 with fine splines?
     
  12. lcwizard

    lcwizard Supporting Vendor

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    The ratio difference would never be felt. You could run one of each. There's more variation in tire diameters after a couple thousand miles
    than the difference between 4:10 and 4:11. 28 psi in the front and 35 psi in the back would be a bigger change
     
  13. lcwizard

    lcwizard Supporting Vendor

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    1/78 could be the changeover. My 1978 I bought new but was produced late 77. It still had a coarse spline pinion. I've broke many axles but only one pinion and it was a 60 series fine spline. It was due to axle wrap and u-joint bind. I'm much more careful with that now. I cut and turn
    or shim everything that's even suspect. Spring overs are notorious for pinion bind if done wrong but so is a spring under once you get in the 4"
    and above lift range
     
  14. cult45

    cult45 SILVER Star

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    Perfect! Are these front members only or both?
     
  15. lcwizard

    lcwizard Supporting Vendor

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    our third members were always interchangeable front to rear 99% of the time
     
  16. cult45

    cult45 SILVER Star

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    Thanks mate!