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Technical 8 3/4 Mopar Questions

Discussion in 'The Hokey Ass Message Board' started by lake_harley, Sep 4, 2021.

  1. lake_harley
    Joined: Jun 4, 2017
    Posts: 2,159

    lake_harley
    Member

    Will a full spool for a 8 3/4 Mopar 3rd member fit all of the cases, including a 741 case?

    Also, I've read that a Dana 60 29 spline pinion coupler (or yoke) will also fit and work on a 29 spline 8 3/4 pinion, but a 8 3/4 yoke won't fit a Dana 60 29 spline pinion. Reason stated in what I've read is that the spline angles are just slightly different, but the Dana 60 coupler or yoke would still engage the 8 3/4 pinion well enough to work. Can anyone comment or verify from experience?

    FWIW...the application would be in the neighborhood of 250-300 HP.

    Lynn
     
  2. saltflats
    Joined: Aug 14, 2007
    Posts: 12,592

    saltflats
    Member
    from Missouri

    Spool will work in any.
    You should be able to get couplers for any 8 3/4 pinion.
     
    lake_harley and oldiron 440 like this.
  3. 73RR
    Joined: Jan 29, 2007
    Posts: 7,174

    73RR
    Member

    Just curious...why a spool for 300hp?
     
    lostviking likes this.
  4. lake_harley
    Joined: Jun 4, 2017
    Posts: 2,159

    lake_harley
    Member

    Front engine dragster. Nothing blistering though, mostly for fun and bracket racing.

    Lynn
     
    stillrunners likes this.

  5. lake_harley
    Joined: Jun 4, 2017
    Posts: 2,159

    lake_harley
    Member

    Anyone have any experience or knowledge of the Dana 60/8 3/4" pinion yoke or pinion coupler interchange or spline compatibility?
     
  6. dan31
    Joined: Jul 3, 2011
    Posts: 1,097

    dan31
    Member

    Give Dr. Diff a call ,they specialize in Dana 60 and 8 3/4 stuff.
     
    lake_harley likes this.
  7. lake_harley
    Joined: Jun 4, 2017
    Posts: 2,159

    lake_harley
    Member

    Since my last post I talked with someone at Mark Williams Ent. and after a brief conversation I felt confident enough that it would work so I got a MWE 29 spline Mopar pinion coupler. Did a quick test fit and all seems well on my 29 spline 741 pinion. The Dana 60/29 spline 8 3/4" pinion similarity question isn't really answered but at least I got the coupler I needed.

    Lynn
     
  8. hemihotrod66
    Joined: May 5, 2019
    Posts: 968

    hemihotrod66
    Member

    My little knowledge of these rears is 742 and 789,, 8 and 3/4's are the ones to use...Larger pinions...Spools with the right bearings should fit in all of the mopar dropout 8 and 3/4s... I have a 489 in my hotrod with a crush sleeve eliminator...A 742 rear doesn't have a crush sleeve...It is favored by most 8 and 3/4 users for that reason....
     
  9. greybeard360
    Joined: Feb 28, 2008
    Posts: 2,074

    greybeard360
    Member

    There are 4 yokes that fit 8 3/4 and dana 60.
    10 spline small and large u-joint.
    29 spline small and large u-joint.

    From my recollection most dragsters back in the day ran open differentials. From what I was told it was to keep the dragster from making a hard turn if it broke an axle.
     
    stillrunners and b-body-bob like this.
  10. Perry Hvegholm
    Joined: Apr 16, 2018
    Posts: 118

    Perry Hvegholm
    Member

    Not that the OP asked, but some misinformation was posted in reply. The 741 case is the smallest and weakest of the 8 3/4 pinions. The 742 was an improvement, but only marginally. The 489 case is the beefiest and strongest pinion of all production 8 3/4 rear ends. And the most sought after.

    The 741 will hold up just fine to your 300 horse dragster, though.
     
  11. desertdroog
    Joined: Nov 16, 2001
    Posts: 1,020

    desertdroog
    Member

    The 741 Pinion is larger than the Ford 9 inch Pinion. It isn't a slouch, and due to the way MoPar 8 3/4 rears are set up, don't rob the same horsepower a Ford does.

    Information for other interested parties, if you have a 741 and are only doing street use, keep it. They are still very stout even in some race applications.

    http://www.doctordiff.com/blog/tech-info/rearend-pinion-comparison/
     
    b-body-bob likes this.

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