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swapping gears

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by deothrwhtmt, Apr 23, 2001.

  1. deothrwhtmt

    deothrwhtmt Registered Member

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    I have two 12 bolt axles and I want to switch gears from one to the other. I know the 3.73 geared axle has smaller dia. tubes than the other which has +9.xx" tube dia. an a 2.73 ratio. Are all 12 bolt axles 30 spline? Please help a newbie out.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Almost positive the carrier (what the ring gear is bolted to) has to be used with the respective gear set, since the 2.73 and 3.73 have differenct (AFAIK) carriers. Buy a rebuild set and have fun.


    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  3. 90K5

    90K5 1/2 ton status

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    All 12 bolts are 30 spline.....I suggest switching the whole axles.

    90K5

    See my truck at <A target="_blank" HREF=http://albums.photopoint.com/j/Albumindex?u=1329584&a=9886502>http://albums.photopoint.com/j/Albumindex?u=1329584&a=9886502</A>
     
  4. deothrwhtmt

    deothrwhtmt Registered Member

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    Thanks guys. 90K5 I was wondering what you meant by "whole axle". Can anyone give me a heads up on the 2.73 to 3.73 carrier compatibility. Will a posi-unit that had 3.08 gears work with 3.73 gears?
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Almost 100% sure it will not. Check out summit or someone and see if 12 bolt ring and pinions are dependent on carrier. If they are, then you can not interchange the 3.08 carrier...usually the breakdown was like 2.29-3.23 or so, and 3.42 and up.



    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  6. ftn96

    ftn96 1/2 ton status

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    Well, here is the fun part. They make say a 4.10 gear set that will fit on a series 3 carrier. And they also make a series 4 4.10 gear set. IF you are not sure what carrier series you have, you will just need to measure or tkae the gears of and try to swap them. If the holes line up the your good to go. If not htne it wont work. There maybe a way to identify from a number or something on the carrier to tell you what series they are but Im not that educated with the 12 bolts yet.

    Will work for beer, parts and tools.
    90 Jimmy 350TBI-TCI 700R4-241-33" BFGs-10 bolts w/4.10's,
    <A target="_blank" HREF=http://www.nashvillek5.freeservers.com>http://www.nashvillek5.freeservers.com</A>
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    Your probably going to see the 2.73, 3.08 etc listed as "2 series" carrier, which means 3.08 and 3.73 carriers are not interchangeable. Unless they don't follow the same pattern as the 8.5" diffs....I know that Richmond and the like make gears such as 4.10 that fit on the 2 series carrier, although thats not his intention, and its quite a bit of added expense. Probably cheaper just to get a locker or something for the open carreri.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  8. ftn96

    ftn96 1/2 ton status

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    Yeah, I was using that as an example. Someone in the past may have ordered a special 3.73 for that size carrier which may not have been the normal carrier for a 3.73. So they may be inter changeable. You see what Im trying to say, or am I just confussing the hell out of this whole post? LOL!!!

    From my understanding, please correct me if Im wrong.
    The norm is 3.08 and less is series 2, then 3.09 up to 3.42 would be series 3 and then 3.73 and up would be series 4.
    So in a since his 3.08 carrier that he is running now would probably be a series 2, and the 3.73 could be a special for a series 2, but maybe not. So I would say you'd have to try for the fit and see unless there is a number or something to identify without the trial and error method.
    Does this make since dorian?

    Will work for beer, parts and tools.
    90 Jimmy 350TBI-TCI 700R4-241-33" BFGs-10 bolts w/4.10's,
    <A target="_blank" HREF=http://www.nashvillek5.freeservers.com>http://www.nashvillek5.freeservers.com</A>
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    I think you are right : ) Again, not knowing the SPECIFIC breakdown, it's a little tough to be authoritative..but in the Summit catalog, for say the 7.5" GM rear axles, you will see a listing for 3.73 twice..one for the 3 series carrier, and one for the 2 series. 2 series would be the numerically LOWER carrier application. The ring gear is either thicker or thinner to make up for the difference in carrier width.

    I can see what you mean about them changing the gears possibly. Should be very easy to tell by looking at teh side of the ring gear. All GM ring gears, andprobably aftermarkets have the ring/pinion ratio on them. Remembering back, there is either "GM" stamped in the same location, or if there is not, there is ALWAYS a whole bunch of other "official" looking stamps. Again thats not a definitive test, but pretty unlikely its aftermarket in the first place. Axle code on the axle tube would tell you what ratio it originally had.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     

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