Advise needed on broken posi

Discussion in 'Transmission & Driveline Topics' started by BC_Homegrown, Apr 4, 2021.

  1. BC_Homegrown

    BC_Homegrown Member

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    Hi all, I have a few broken teeth on the upper spider in a 8.5 posi unit in my 73. I was hoping to possibly get some suggestions on the best path forward from people with more experience as I've never done any diff work (taking the axles out was the furthest I've ever gotten) and the knowlege on this forum is incredible. Here is a picture of the carnage: 1.jpg


    The rest of the gears look in good shape. It is in a new to me 73 that apparently used to be drag raced with slicks. Its got richmond 3.73 gears, th350 and a 454, maybe around 400hp. Will be driven 90%street with a few test and tune days at the track with street tires. I would prefer doing the work myself but my mechanical skills are limited to google, youtube and learning stuff on here so I don't think I want to try to mess with setting backlash and the paint stuff(yet). I would just take it to a shop if I had to do that. Also I have a moderate budget but nothing crazy.

    So based on that what is the best solution in your guys' opinion? Get the oem posi repaired professionally? Or is it possible to change just 1 spider gear without removing the whole unit? But then why did it break to begin with... or buy an open carrier and put a lunchbox locker in it? or bite the bullet and buy a full locker? Or close it back up and forget I saw anything :D

    Any suggestions would be appreciated, thanks gents!
     
  2. 351maverick

    351maverick full time Ebay seller/hustler/car killer

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    that would need completely disassembled since metal shavings will be everywhere
     
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  3. Fbird

    Fbird Veteran Member Lifetime Gold Member

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    i would RECOMMEND a full tear down and evaluation as the "missing" pieces went SOMEWHERE! Now that doesn't mean you need all new stuff.....but you gotta know what is good and what isn't or whatever you do to "fix" it will be short lived. THEN you will need EVERYTHING. The only thing that gets touchy BEFORE you start removing stuff is MEASURE the BACKLASH. This MAY be needed in the event you replace any bearings you can reset-up the gear with minimal issues.(NOISE) This is NOT a difficult task as long as you remain organized and patient.
     
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  4. big gear head

    big gear head Veteran Member

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    There are no replacement gears for that unit that I know of, so it's going to have to be replaced unless you can find another one and get the gears out of it. Sometimes you can find a 2 series cheap and take the parts out of it. If you can't find replacement gears then I would recommend a new Eaton Posi or Truetrac. You need to check the backlash before you take it apart so that you can set it back where it is now. You will need bearings and shims for the new differential. Read post number 2 in this thread. https://nastyz28.com/threads/change-to-posi.19773/
     
  5. BC_Homegrown

    BC_Homegrown Member

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    Thanks for the replies fellas much appreciated. I've been researching this so much my head hurts so it helps having people with the experience.

    351Maverick: That was my first thought but I've cleaned out the case and there was lots of shavings in the oil but no large chunks of teeth, I'm thinking the PO probably cleaned it out and was running it like that for a while or just to sell it maybe, I can't see any other visible damage other than the spider.

    Fbird & Biggearhead: Thanks I've been researching LSD units and the Eaton sounds like the way to go, although there is a Yukon on amazon for a few hundred less, any experience with those?

    I'm guessing to measure the backlash I will need a dial bore gauge so there's that plus an impact for the crush sleeve, and an inch lb torque wrench that would be needed to do the job?
    I'm all about learning how to do stuff but this one seems a bit tough for a novice, to do it right anyway. I'll give the shop a call and see how much they'll bend me over for, if it's outrageous I might attempt it. Thanks again for the suggestions guys, happy Easter!
     
  6. big gear head

    big gear head Veteran Member

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    Check the link that I posted. it's all explained there. You will need a dial indicator with a magnetic base. The rest of it is just if you replace other parts.
     
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  7. BC_Homegrown

    BC_Homegrown Member

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    Oh forgot to mention that's a fantastic post you pointed me to Biggearhead, extremely informative without sounding like gobbledygook. I have it saved and will use it for sure if I attempt this, thanks!
     
  8. biker

    biker Veteran Member

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    I have a Yukon with 3.73 in my 81. I checked for an opinion from BGH first and he says they are good. Mine works great. Good reviews from other sources as well.
     
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  9. BC_Homegrown

    BC_Homegrown Member

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    Awesome thanks Biker, the price difference is substantial between Yukon and Eaton was just wondering if the quality is much different.

    Sounds like it will be cheaper to buy new than repair the original posi so I've ordered a dial bore gauge and will be attempting the job myself. Still shopping for LSD units but amazon seems to be the cheapest in Canada from what I've found.

    I'm sure you guys will hear from me if there's any issues haha. Thanks again to everyone for the help, love this forum!
     
  10. biker

    biker Veteran Member

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    You wont be disappointed with the Yukon if you go that route. Mine is quiet and hooks up both tires every time. Or allows me to do donuts to my hearts content. Often.
    I think the Yukon and Eaton are exactly the same design, I believe the parts are even interchangeable.
     
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