Posi Differential Donor Options?

Discussion in 'Transmission & Driveline Topics' started by MMFS, Oct 9, 2019.

  1. MMFS

    MMFS New Member Gold Member

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    Thought my '77 had posi until I got her running and found out I was mistaken. I know it's a 8.5" 10-bolt; what donor cars should I be looking for to rob the posi from?
     
  2. camaro71/holland

    camaro71/holland Veteran Member

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    Why buying a worn out unit? Just get a new one. Eaton posi would be a good option to start with if you're looking for a clutch type unit .
     
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  3. Gary S

    Gary S Administrator Lifetime Gold Member

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    If you get a used posi, you first need to know if your rear end is a series 2 or a series 3. That depends on what ratio gears are in it. Then, the used ones can be expected to be worn out since the clutch type posi was used in cars, and cars with 8.5" rear ends are so old that they are difficult to find today and worn out. The 8.5" posi used in later pickups is the Gov Lock which is a disaster waiting to break if you put it in a car where you might spin the tires on pavement.
    As stated, a new Eaton would be more cost effective in the long haul.
     
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  4. MMFS

    MMFS New Member Gold Member

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    Not planning on buying anything. My family has a salvage yard I hope to pull something from.
     
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  5. big gear head

    big gear head Veteran Member

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    2nd gen Camaros and Firebirds (except '70), '71 - '88 police cars and station wagons. No trucks. Your car will have 28 spline axles. As stated above, you must know what your gear ratio is before you can start looking. The 8.5 uses a 2 series for 2.41 to 2.56 gears and a 3 series for 2.73 to 4.56 gears. The factory Traction Lock has the casting number 410409 for 2 series and 410408 for 3 series.

    If you are using the "turn one tire and see which way the other one turns" method then you may get fooled. Many times a damaged standard differential will turn both tires the same direction, and many times a limited slip differential with worn clutches will let the other tire turn the other direction. The only way to know what you have is to remove the cover and take a look inside.

    You are going to have to check and set the backlash and bearing preload when changing the differential. You will need a dial indicator with a magnetic base and a shim kit for this.
     
    Last edited: Oct 9, 2019
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  6. Gary S

    Gary S Administrator Lifetime Gold Member

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    If you expect to get a complete differential for your car, it needs to be a 71-81 Camaro or Firebird rear end. Only those will swap into your car. If you expect to rob just the posi unit from inside another car and install it in your existing differential, any of those that big gear head listed will work. Also, the ones from 73-77 Chevelle and Monte Carlo would have parts that fit into your existing rear end.
     
  7. MMFS

    MMFS New Member Gold Member

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    Thanks for the help, no luck on the posi, but I did find a 638 and two 010 350s and a set of 906 Vortec heads already pulled out... Several other 350s, TH350 and TH400 and possibly a couple of BBC still in vehicles... My dad passed away in July and then the business shut down; my Uncle is scrapping everything I don’t want to keep, but it’s all stacked and packed so much I can’t get to everything or always open the hood. After he hauls off what I’ve already marked, I’ll have to come back and go through the rest.
     
  8. big gear head

    big gear head Veteran Member

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    2nd gen Camaro/Firebird stuff is getting more valuable. Even things like bolts and screws are worth something. People who are restoring these cars want bolts with original head markings and all of the correct clips and nuts to go with them. Even if a car is damaged beyond repair you can strip all of the nuts, bolts, clips and screws and sell them.
     
  9. MMFS

    MMFS New Member Gold Member

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    No Camaros in our yard, unfortunately...
     
  10. big gear head

    big gear head Veteran Member

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    If there is any GM stuff from the '60 and early '70s then strip them before crushing.
     

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