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  •  » FYI Ford, Classic Mustang Tech Discussion
  •  » 66 Pony 28 or 31 spilne rear axle

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    7/13/2019 1:17 PM  #1

    Texag70
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    Registered: 7/06/2019
    Posts: 12

    66 Pony 28 or 31 spilne rear axle

    Moving along on restore and upgrade of 66 Mustang coupe.  Will have a 302 (300+ hp) and Tremec 5 speed.  With 9" Ford rear end and Richmond 3.50 which axle is best and why--28 or 31 spline?  Thanks in advance.

     

    7/13/2019 2:53 PM  #2

    Bolted to Floor
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    From: Houston, Texas
    Registered: 4/01/2013
    Posts: 2,017

    Re: 66 Pony 28 or 31 spilne rear axle

    I’m gonna stay away from best and say that a 28 spline axle will work just fine for what you are doing. No need for the extra expense.

    If the 9 inch is factory width, find an 8” rear end for your car, pull those axle shafts and install in the nine. They are supposed to be the same. Axle bearings retainer plates could be a factor.

    John  -- 67 Mustang Coupe 390 5 speed
     

    7/13/2019 5:04 PM  #3

    lowercasesteve
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    From: Auburn, Ca
    Registered: 4/01/2013
    Posts: 1,256

    Re: 66 Pony 28 or 31 spilne rear axle

    Bolted to Floor wrote:

    I’m gonna stay away from best and say that a 28 spline axle will work just fine for what you are doing. No need for the extra expense.

    If the 9 inch is factory width, find an 8” rear end for your car, pull those axle shafts and install in the nine. They are supposed to be the same. Axle bearings retainer plates could be a factor.

    X2

    Actually, if you do not have the 9" yet, keep your 8".  Some of the Ford vans (Econoline) had 3.40 rear ends that should fit the bill just fine.

    The 8" can handle 400hp, so, if you are not racing, keep it. Spend the money on running gear.
     

    Last edited by lowercasesteve (7/13/2019 5:06 PM)

    Original owner - 351w,T-5, 4whl disks, power R&P
     

    7/25/2019 8:29 AM  #4

    MS
    Forum Originator

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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 12,294

    Re: 66 Pony 28 or 31 spilne rear axle

    But, IF you are going to buy a new 9” rear end, have it built for 31 spline. The difference in cost at that time is negligible. The 31 spline axles are way stronger.  Should you ever need a different differential, most pickups came with 31 spline.

    I made the mistake of starting with 28 spline axles. Twenty years later, I have over 500 hp and made the upgrade to 31 spline at alot more expense.

    An 8” rear would work fine with the combo you are planning.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

     

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  •  »  66 Pony 28 or 31 spilne rear axle

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