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weird 12 bolt rear-end/u-joint question

Discussion in 'The Garage' started by big d, May 20, 2004.

  1. big d

    big d 1/2 ton status

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    i got a 79' blazer, with 12 bolt rear end. i went to replace all u joints in it, and the very rear one is weird. it is not the proper one the parts store's say it should be. its larger on one side than the other. also, there is also /forums/images/graemlins/thumb.gif /forums/images/graemlins/k5.gif /forums/images/graemlins/usaflag.gif casting marking on the inside of the axel that says 85 g.m.. does this mean anything ? could the rear end be swapped from something non-truck ? conversion joint maybe ? this truck is all stock as far as this stuff goes to the best of my knowledge, but the truck has been around /forums/images/graemlins/rolleyes.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/ignore.gif(many owners). thanks for any info in advance.
     
  2. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    sounds like a conversion joint. the best think to do would take the old ujoint to the parts store and they should be able to match it up.
    IIRC the 12 uses a 1310 joint, the drive shaft might have been swapt in from a 1330 truck /forums/images/graemlins/dunno.gif
     
  3. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Is it actually a 12 bolt ? count the number of bolts on cover. I have a 83 which originally had a 10 bolt and when I installed my 12 bolt, the U-joint on mu driveshaft was too big. This necessitated a conversion u-joint , one size larger for my shaft, one size smaller for my 12 bolt. I can look in my trail box and get part number for my spare. /forums/images/graemlins/k5.gif
     
  4. big d

    big d 1/2 ton status

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    ya, it is a 12 bolt. truck could have originaly had a 10 bolt, i guess. i would appreciate the part number, thanks. /forums/images/graemlins/thumb.gif /forums/images/graemlins/k5.gif /forums/images/graemlins/usaflag.gif
     
  5. big d

    big d 1/2 ton status

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    thats the problem, p.o. did not have correct u-joint in there and there was slop, hence why i was changing them. i was just wondering if any one else has came across this because i know g.m. some times did weird stuff. thanks. /forums/images/graemlins/thumb.gif /forums/images/graemlins/k5.gif /forums/images/graemlins/usaflag.gif
     
  6. Muddytazz

    Muddytazz 1 ton status

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    I would have to take a guess and say someone swapped in a 3/4ton driveline
     
  7. R72K5

    R72K5 Banned

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    some of the late 70s K20's have two sizes of caps on some of the U joints i know, either the rear most one on the rear driveshaft, or also one of the front shaft ones too, i cant remember now,
    this 79 K20 out here im sure has this deal on it too.

    also the last year that you would see a factory installed 12 bolt rear axle would be in 82, but in '77 gm started changing over to 10 bolt in models cept vans in which were already starting to see 10 bolts before '77, 77 was a year of more changes than usual for GM trucks,

    good luck
     
  8. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Well, I rembered the part numbers are here on ck5. There is a post in members section ( tech articles ) . Glad I didn't have to dig through my box ( packed well, only used often stuff on top ). Anyways Tim posted this :

    1310 (12 bolt) to S44 (10 bolt) # 3-3130

    Don't know if it helps, but some parts chains have there own numbers , but can go off of that one to find em.

    You have a 1979 , should of been stock with 10b front and 12b rear. So someone could of changed some things like yokes or shafts if you are not previous owner /forums/images/graemlins/k5.gif
     
  9. big d

    big d 1/2 ton status

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