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12bolt vs 10bolt u-joint

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 87Blzr, Jun 1, 2000.

  1. 87Blzr

    87Blzr 1/2 ton status

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    A long time ago I had to part out a 77 Blazer I had but kept the front and rear ends. A few years ago I put the 12 bolt from the 77 in my 87. The 87 had pretty good size u-joints compared to the 12 bolt. Eventually a u-joint broke which in turn made the driveshaft go around frantically until I could stop it. In the few seconds it took out my exhaust, a brake line, broke the yoke out of the rear end, and split the transfer case in half. My daily driver at the time I did what i had to do to get it going again including getting another driveshaft, had it lengthened a inch or so and had the end welded on to match the new yoke for the rear end. That rear u-joint on the 12 bolt is so much smaller than the factory 87 and it goes bad so much quicker despite being at a much less angle than the front u-joint on the rear shaft. Sorry to ramble but the question is, is there a way to upgrade this, cheaply? Upgrading to a heavier duty rear shouldn't be compromised by a lighter duty u-joint.

    87 K5 Siverado, 68 SS 396 Camaro
     
  2. BIGJ

    BIGJ 1/2 ton status Author

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    I had this same problem when I built up my 12 bolt a couple of years ago. I bought a new pinion yoke. It was a 1310 size. That "should" be the factory size for the 77. Some time in the 80's (according to the local spicer dealer) GM switched to a joint size called 3R. It is a little bigger than the 1310. So, because if the size difference, I had to buy a 3R/1310 combo joint (that's why the 10 bolt u-joint was bigger). You could go to an even bigger size like 1350 and have the driveshaft changed but a new 1350 yoke is around $100.00 or more for the 12 bolt. I tried to find a 3R size yoke for the 12 bolt and couldn't find one in the short time I had. Try six states http://www.sixstates.com or dennys driveshafts http://www.dennysdriveshaft.com. They should be able to help with the problem.

    BIGJ
     
  3. 87Blzr

    87Blzr 1/2 ton status

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    Thanks for the info. I didn't realize they made different yokes for the rear. At the time, I had to have the driveshaft place weld on a new end to the driveshaft and get a new yoke for the rear. That would have been the time for the update and I remember mentioning it to them but don't remember the response. They charged me alot and I wasn't happy at the time. I vowed to not go back and now I have another reason. They should have helped further. I asked for help and they knew my setup. Sometime in the future I will have to look for the 1350 yoke for the 12 bolt and find a good driveshaft place to weld on a new end onto the driveshaft. Sometime when money permits that is. Thanks again for the info, at least I know a option


    87 K5 Siverado, 68 SS 396 Camaro
     
  4. BIGJ

    BIGJ 1/2 ton status Author

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    No problem. It really is a shame that some shops don't want to try and help you out. It was like trying to pull teeth to get info from one driveshaft place around here. Needless to say I didn't go back. Just glad to help out.

    BIGJ
     
  5. BigBadBowTie

    BigBadBowTie 1/2 ton status

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    There's a guy at six states that know the anwser to this. I lost my part #'s or I could help you. Basically you take a standard 10 bolt youke & a different oil seal & thats it it's a bolt on change. I called to get new driveshaft, & instead of selling me a more expensive part he explained how to change the yoke to use the larger u-joints from the 10bolt..Worked great.

    Rick
    86 K-5
    http://www.coloradok5.com/RMcPherson.htm
     
  6. 87Blzr

    87Blzr 1/2 ton status

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    I'll have to look into that. Then I would only need a new end welded on rather than a new yoke, cheaper. However I thought I read somewhere that the splines on the 12 bolt pinion are smaller than the 10 bolt. I don't know, I guess thats why I have to look into it.

    87 K5 Siverado, 68 SS 396 Camaro
     

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