8.5 rebuild and upgrade. Advice and guidance needed

Discussion in 'Transmission & Driveline Topics' started by Camaromurph, May 17, 2020.

  1. Camaromurph

    Camaromurph Veteran Member

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    About to start the rebuild and upgrade of the 8.5 10 bolt in my 79 Z. Here is what I picked up.

    30 spline 8.5 detroit trutrac
    AAM 3.42 r&p. Appear to be 2 cut
    Moser 30 spline axles
    Yukon 8.5HD install kit Includes all new Timken bearings.
    New Timken axle bearings and seals
    Moser 1350 pinion yoke

    The original rear was a 3.42 open.

    1st question of many I assume, I disassembled the original pinion bearing and it had a 0.038” shim. Is this a good place to start with the shim on the new pinion?
     
  2. Zspoiler

    Zspoiler Veteran Member

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    My 1979 Z-28 Super T-10 .377 supercharged small block chevy .Has a 8.5 bolt rearend with a Moroso "Brute Strength" posi .Mosier 30 spline axles .Chevrolet 3:42 gears and yoke .I have had this for years with no issues .Not sure about the rest I had a friend with his own shop do it .
     
  3. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

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    Have the tubes welded properly
     
  4. big gear head

    big gear head Veteran Member

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    Yes, .038 is a good place to start. I was also going to recommend welding the tubes, and brace the spring perches if this will be run hard. Remember that the center is cast iron and needs to be welded by someone who knows how to weld this. The AAM gears probably are 2 cut.
     
  5. Camaromurph

    Camaromurph Veteran Member

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    Great, will start with 0.0385” as that is the closest pair of new shims I have.
    Next question - I was just checking the new moser pinion yoke on the new pinion. I was just setting it over the splines and I could not really get it to drop down on the splines more than about 1/16”. I checked in on the old pinion and same thing. So I took the old yoke and tried it on both pinions and it went down a little over 1/4” before stopping. Is this normal for a new pinion yoke to not drop down the splines very much? At first I thought it wouldn’t go on at all but once I got it lined up perfectly it did engage about 1/16”.
     
  6. Lowend

    Lowend Administrator. .a car, a man, a maraca. Staff Member Lifetime Gold Member

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    If you're going to track days or autocross, this is the time to heat camber the rear end
    Info here
     
  7. camaro71/holland

    camaro71/holland Veteran Member

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    Yes, there is tightness in there with new parts and that's good. On trial assembly you use the old nut to push the yoke on the pinion. On final you obviously use the new nut from the kit.
    To pull the yoke you need a puller. There are dedicated ones, but a large bearing puller will also get the job done.
     
  8. Fbird

    Fbird Veteran Member Lifetime Gold Member

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  9. Camaromurph

    Camaromurph Veteran Member

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    Super shims, check. I thought they were in the Yukon kit but hadn’t checked to confirm after I got it. I just looked and that’s what they are.

    Next question - I have the rear end out now and am debating on if I do the gear install out of the car with the rear end on jack stands or would it be easier to complete the Install with the rear end installed in the car?
     
  10. big gear head

    big gear head Veteran Member

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    It's easier out of the car if you have a way of holding it while you tighten the pinion nut. It's no fun doing this under the car.
     

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