1. brotherGood

    brotherGood Well-Known Member

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    I'm going to assume they're the same dimension as the 8.75s as far as fitment go. Is there any advantage to usinget one of these over a factory M 8.25? The B body has a sure grip, my current rear doesn't. Any help is greatly appreciated
     
  2. BudW

    BudW Moderator Staff Member

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    The center of axle shaft to center of universal joint dimensions are:
    7¼” 10.09”
    8¼” 11.69” (propeller shaft about 1.60” shorter than a 7¼”)
    8¾” 12.35” (about 0.86”shorter than an FMJ 8¼” and 2.26” shorter than a 7¼”).
    '69-70 B-body 8¼” 12.35 (same as 8¾”)

    The ’69-70 B-body did have an 8¼” that was behind 318’s and 2-bbl 383’s only.

    Their dimensions are:
    54.937” from backing plate to backing plate (the same as ‘68-69 B-body 8¾”)
    44” perch center to perch center
    12.35” center of axle shaft to center of U-joint (the same as 8¾”)

    I hadn’t actually worked on one of that year 8¼” – so don’t first hand know if or what internal parts are the same, or not as, FMJ 8¼”. I’ve seen a few, though. The pinion gear is a wee bit longer.
    I suspect it will work just fine, with a shorter propeller shaft length

    FYI, FMJ differential specs (7¼” or 8¼”), not mentioned earlier.
    44.460” Perch center to center
    54.340” backing plate to backing plate.
    BudW

    Edit: Any other year B-body 8¼” will require shortening and perch re-location.
     
  3. MiradaMegacab

    MiradaMegacab Well-Known Member

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    Perch holes are different too. Grab the B body shock plates and eliminate the ISO setup.
     
  4. BudW

    BudW Moderator Staff Member

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    Yes. Definitely get the shock plates - even if you don’t use the differential.
    If you don’t use them, then sell them here. I wouldn’t mind another set.

    There are How-To’s on how to eliminate the ISO’s, out there.

    In this case, change the leaf spring bolts (using clamps on existing leaf springs first).Then you can either push the leaf springs ¼” apart per side OR slot out the older shock plate holes 0.22” per side and everything will slide into place.

    I recommend slotting the plates - or you may experience leaf spring bushing wear issues.
    BudW
     
  5. brotherGood

    brotherGood Well-Known Member

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    I'll talk to him about the shock plates. Would it be worthwhile for me to pick it up and just swap the SG/gears into my current axle? I dont really see the sense in going from one 8.25 to another 8.25, but if itd be much more of a hassle to simply swap gears, i might as well.

    I figured, at the very least I could use the SG, and sell it complete with my open diff reinstalled, and sell my spare 3.54 gear set I've got on the bench to make my money back.
     
  6. BudW

    BudW Moderator Staff Member

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    I’ve worked on a lot of differentials – but unless one snuck in on me without me noticing, I don’t recall working on a ’69-70 or ’71-73 B-body 8¼” – so I don’t know about part interchange.

    I do know that if a person is going to build (or re-build) a differential, you might as well put a limited slip carrier into it at same time.

    - - - - -

    According to 1969 DODGE CORONET Auburn Gear High Performance Series Differentials 542072
    The carrier will only fit 66-70 8¼” differentials.
    Note: I have never seen an 8¼ in ’66, ‘67 or ‘68 Chrysler product – and I’ve seen a lot of differentials.

    Further research shows the carrier bearings only fit ’68-70 8¼ differentials – so I suspect the carrier bearing size is what the whole hiccup (limited usage) is about.

    1969 DODGE CORONET Dorman Ring and Pinion Sets 697-356
    The Ring & Pinion gear set shows to fit from ’65 to ’76 8¼” only – which tells me two things.

    The carrier bearing size is what is the limiting factor is on the carrier.
    The length of pinion gear (or bearing size) is also a limiting factor on that, as well.

    As a whole differencial, I think you are good.
    As far as swaping parts, I don't think you are going to get what you desire.
    BudW
     
  7. brotherGood

    brotherGood Well-Known Member

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    So, it's either swap the whole rear, or purchase stock in excedrin? Haha
     
  8. 80mirada

    80mirada Well-Known Member

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    If you search for the parts, and then check application the carrier fits 66-95, and the gears fit 66-2010
     
  9. BudW

    BudW Moderator Staff Member

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    That was the page (link), I thought I had posted.
    Carrier.JPG

    RnP.JPG
     
  10. 80mirada

    80mirada Well-Known Member

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    Your links only show Coronet, not sure why, but if you search by axle type it shows all of the applications. The limited slip is available for less from Doctor Diff.
     
  11. BudW

    BudW Moderator Staff Member

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    I guess a hiccup on Summit's site?
     
  12. brotherGood

    brotherGood Well-Known Member

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    So then I can swap carriers no problem? Ive got a gently used open 3.54 gear set on the bench to go back in..and I'll just sell it to someone looking for an 8.25.
     
  13. 80mirada

    80mirada Well-Known Member

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    Summit's site won't show all of the applications sometimes, it is a glitch in the search engine. Chrysler 8.25"/8.3" magor difference is the two different axle spines (27 & 29)
     
  14. BudW

    BudW Moderator Staff Member

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    Sorry, BrotherGood.
    I wasn't my intention to mislead.

    My question is: my information shows any vehicle that has an 8¾” as well as an 8¼” – they both share the same propeller shaft length (’68 though ‘73ish, ABCE bodies).
    Note: I also have an extensive propeller shaft length database I’ve been working on the last couple of months.

    I suspect pinion gear got shorter in early to mid ‘70’s – but hadn’t looked that close at that, yet (it's on my “sometime down the road” list of things to do in my spare time).
    BudW