Help w/ 7 1/4 to 8 3/4 change over

Early A-Body Discussions

  1. johnmucci

    johnmucci moparmucci

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    Hi, I need some expertise on this issue, I have a 66 dart gt w/ 7 1/4 rear end. I want to change to 8 3/4. What years A body 8 3/4 will "bolt right in"??? I have heard many different opinions. Also, what else would I need to make the change?? thanks!!!
     
  2. caferacerx

    caferacerx BAND MEMBER

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    shock plates, U-bolts, and you need to shorten your drive shaft 2 1/4"
     
  3. pettybludart

    pettybludart Well-Known Member

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    The 67-72 8 3/4 will work,u-bolts,shock plates.When I did the swap,I used the driveshaft from a 73 Dart Swinger 318/904 donor car.It was a direct bolt in.
     
  4. 48limo

    48limo Well-Known Member

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    if you want BBP,4.5",you can use a rear from a 65-67 B body,its a bit wider but bolts right in,ya just cant have big meats
     
  5. Commando66

    Commando66 She's a beaut Clark!

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    Is this measurement for a Dodge or a Plymouth? They have different wheelbases. Best bet is to measure your car and have your original driveshaft cut to the right size.
     
  6. caferacerx

    caferacerx BAND MEMBER

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    this is the difference between a 7 1/4 and an 8 3/4 so wheel base doesnt enter into the equation, a 7 1/4 is 10.09" axle center to U-joint center, and an 8 3/4 is 12.35" axle center to U-joint center, so 12.35" minus 10.09" equals 2.26" or aprox. 2 1/4" that said you are correct it is always better to measure first
     
  7. cudamark

    cudamark Well-Known Member

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    You can add the '66 A-body 8 3/4 to the donor list. If you use the '67-72 rear, you'll need to use your old e-brake cables off the 7 1/4. I've also run across wheel problems in rare cases. Some of the early 13" wheels don't fit over the 10" drums. It's mainly the '64 and older wheels but sometimes the newer cars have had wheels installed from the older cars. The B-body one is not really a bolt-in. The spring perches are spaced 1" farther apart so the spring would be in a slight bind if you use it. Plus the wheels would need to be changed and tire clearance is an issue.
    Mark
     
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    • cosgig

      cosgig MoBro Inc. FABO Gold Member

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      Remember too that in 1970 they changed the position of the brake line distribution block on the rear end housing, making the flex hose too short if you use the 71 and later 8 3/4. I just used a coupler piece provided by a mobile hydraulic hose maker that services disabled roadside semi trucks, he knew just what I was talking about and had the part on hand. I used a 71 rear from a Duster in my 66 Cuda in this example. Otherwise, all other dimensions of the rear itself are the same, except the aforementioned driveshaft length and the shockplates. Geof
       
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      • Dfnsmn34

        Dfnsmn34 Margarita Mike

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        can I add to the questions....I have a 66 cuda and am debating the addition of the 8.75. There is one set up locally that is available...but I am still not clear if this would BOLT right up or not.

        It sounds like I would need a new drive shaft. and my 13 inch wheels might not fit :(

        But I'm not sure about the perches.

        here is the description of the axle locally.
        http://honolulu.craigslist.org/oah/pts/1629375669.html ....picture at link...

        A body rear end set up from 340 duster. It has 741 carrier with 323 posi
        has leaf springs shackles,spring perches that is hard to find and emergency brake
        cables . It is a small bolt pattern. Just bolt up and burn rubber!!!!!!!!!!!
        asking $600.00

        is this too much too?


        Aloha FABO Members!
        Mike
         
      • cosgig

        cosgig MoBro Inc. FABO Gold Member

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        Dfn, any A body rear will bolt right in to your 66 Cuda, just make sure that you get the shockplates for the 8 3/4. You will have to shorten the driveshaft, or in the case of the 66 Cuda, you might need a different driveshaft to shorten as the 66 has a wierd front tube area that may limit the shortening distance. A later A body shaft will not have this odd front tube design(it's almost like a 2 piece with a rubber vibration donut inside, and it tapers). The leaf springs he is including in the sale will also be one inch too long, so just use your existing leafs. Also see my above post about the flex hose. Snag it for the $600.00, that ain't a bad price, especially in Hawaii!!! Good luck with the swap, Geof
         
      • Dfnsmn34

        Dfnsmn34 Margarita Mike

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        Mahalo Cosgig....now to find a shaft!
         
      • cosgig

        cosgig MoBro Inc. FABO Gold Member

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        Too bad you're in Hawaii there Dfn, or you'd be coming by my house to pick up one of these shafts I have "in stock" if you will. On that note, when you get to that point, message me and I'll send you one just for the shipping!!! Geof
         
      • Dhow

        Dhow Member

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        Could some body help me on this issue please.

        I want to change my 69 Barracuda 7 1/4 rear end to 8 3/4 w/ 4.5" inch bolt pattern, cos the one I have has 4" inch bolt pattern.
        What is the right year & model 8 3/4 w/ 4.5" axle will fet my car. as far as I know the 7 1/4 length on my car is 53.200" length based on this chart:

        [​IMG]
         
      • pettybludart

        pettybludart Well-Known Member

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        Dhow,all the A-body rears came with 4 inch bolt pattern.To get the 4.5 bolt pattern,you,ll need to get some aftermarket axels.You can get these from Moser,Strange,Yukon.They all carry these axels,if ordering?Don,t forget to mention the size of brakes you,ll be useing.Good luck.
         
      • caferacerx

        caferacerx BAND MEMBER

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        if you want 5X4.5" get an 8 1/4 they are all big bolt and easy to find cheap
         
      • ChuckDock

        ChuckDock FABO Gold Member FABO Gold Member

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        I know this is a really old thread, but would leaf springs need to be changed as well?
         
      • pishta

        pishta I know I'm right....

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        No but shock plates need to be 8.75 tube sized.
         
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        • ChuckDock

          ChuckDock FABO Gold Member FABO Gold Member

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          Ok, good deal. I have those already from a previous order. I'm sure these springs need to be replaced either way, but for now I can "test", lol.
          Thanks!
           
        • Slantsix64

          Slantsix64 Well-Known Member

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          I ran an early b body 8.75 bolt in, just moved perches and later I had steelies made with more back space, stock big bolt steelies fit but only a 205 70 14, I didn't not roll the lip or anything. Here it is with stock big bolt steelies. Also ran the 73 and up disc brakes with match upper control arms.

          IMG_0777.JPG

          IMG_0778.JPG
           
        • dibbons

          dibbons FABO Gold Member FABO Gold Member

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          Just for contrast, I used a '70 Challenger 8 3/4 sure-grip in my '65 Valiant. Had to modify driveshaft, move leaf spring pads, flare wheel wells.

          65 Valiant1 edited.jpg
           
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          • grumpy old fish

            grumpy old fish Well-Known Member

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            DoctorDiff Drivetrain Components has every thing you need.
             
          • Slantsix64

            Slantsix64 Well-Known Member

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            You just need a 8 3/4 housing for an abody and year but as long as it's an abody 8 3/4 and buy new axles with the big bolt pattern
             
          • ChuckDock

            ChuckDock FABO Gold Member FABO Gold Member

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            Plus shock plates, and then shortening the driveshaft. Then you have to think about brake drums and back plates as they will be different on the 8 3/4. So that usually means bake cylinders, shoes, all the springs, etc for a complete brake job. I'm doing the same conversion now. I didn't do the BBP though since we can still find wheels like cragars from summit that are up to 15x8 in size. I went to the big yokes as well on the rear end and will do the same for the yoke sliding into the trans.
            And while its all apart, may as well refresh the leaf bushings and maybe replace the leafs if they are old.
            Also, my sure grip (actually powr-lok, Dana part) clutches were pretty fried so those plus all the bearings were replaced. That was 500 bucks to get done, plus the ring and pinion from a 3:55 were taken from 1 pig and put into this one.
            So, it adds ups really fast....
             
          • pishta

            pishta I know I'm right....

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            Too bad someone doesnt make a bullet proof 7.25 spider gear..thats what blows, correct? My 7.25 SG looked like a shark bit the ring gear and pinion was barrel smooth, not sure if the spiders survived, or locked up the rear causing the pinion debacle. Lame 2.76 replacement axle was a wet blanket thrown on that 340. Could not break traction with that rear and the 10" tires i had. Cam was too soft down low. Hauled ass on the highway though!
             
          • GGs66GT

            GGs66GT FABO Gold Member FABO Gold Member

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            Wheels I had a set of 14x5 s.b.p steels on this until I changed the front brakes to 73 up disc
            So now I have Rally wheels 15x7 l.b.p on the front and 15x7 s.b.p. on the rear 7 1/4 axle.
            This will change to a 15x8 l.b.p. when I install the 8 1/4 .
            Tires I'm running now are 205/65Rx15 . When I change the rear end I hope to run 245/60R15 on the rear. Dart Left.jpg Dart Left.jpg Dart lr.jpg
             
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