1970 duster slant six 8.25 rear swap

Slant 6 Engines

  1. travism

    travism Well-Known Member

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    Hey guys I was looking into doing a 8.25 rear end swap on my 1970 duster slant 6, it has a 7.25 on it and ive bin hearing a lot of horror stories about them blowing up when you drive too hard. my question is will any 8.25 rear end just swap onto my car?
     
  2. 65 Dartman

    65 Dartman FABO Gold Member FABO Gold Member

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    A 73-76 A Body 8.25 is pretty much a direct swap. Use the 8.25 shock plates. You will have to shorten the driveshaft a couple of inches.

    An 8.25 from any other platform is going to be too wide. Yes they can be narrowed and replacement axles sourced - expensive! Also don't forget that the 8.25 is a LBP rear end so you may want to upgrade your front brakes to the 73-76 A Body disc brakes
     
    Last edited: May 2, 2017
  3. barbee6043

    barbee6043 barbee 6043 FABO Gold Member

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    drive it with the 7 1/4 and treat it like ya should and it willl last a long time!??????????????
     
    • Agree Agree x 1
    • Shogun1332

      Shogun1332 Member

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      I don't think you're in danger of "blowing up" the 7 1/4 unless you're planning to build your slant to some extreme. Most people who advise to swap out the 7 1/4 do so because they are smaller and don't hold up as well to higher power levels/racing.

      Unless you're gonna be running boost or some other way of making much larger power numbers, you'll be fine.

      Now if you're planning a V8 swap for the future but you have an 8.25 right now, I'd say go ahead and get it done, as that's one less thing you'll have to worry about down the road

      EDIT: Its worth noting that if you're dead set on doing the swap anyway, Dartman 65's info is what you're looking for.
       
    • travism

      travism Well-Known Member

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      I got a stupid question what does LBP mean?
       
    • travism

      travism Well-Known Member

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      That's not gonna happen I'm probably going to do some burnouts and go to the drag strip with my friends and have some fun
       
    • diymirage

      diymirage HP@idle > hondaHP@redline

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      Large Bolt Pattern
      5 on 4.5 instead of 5 on 4

      Important to know, because you would hate to swap out the rear only to find out your wheels don't fit
       
    • travism

      travism Well-Known Member

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      Thanks, I got a question about wheels now I was planning on getting some magnum 500 wheels would a 15"x10" wheel fit on the rear of my 1970 duster?
       
    • diymirage

      diymirage HP@idle > hondaHP@redline

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      Of all the people on here you had to ask me
      (Wait untill @72bluNblu gets a hold of this...and posts a picture )

      In short, no, not unless you move the springs inboard OR let the wheels hang outside the tubs

      8 inches is about the maximum width on a stock duster, with a 285 tire
       
    • 72bluNblu

      72bluNblu FABO Gold Member FABO Gold Member

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      :lol:

      Lol, yeah what diymirage said. 15x8's with the stock spring locations. And I'd even say 275's unless you're willing to trim the quarter lip back. 275's are tight if you're at stock height or lower. Now, if you're looking for the '70's street freak look with the back end of the car up in the air and the tires hanging out, 15x10's will work just dandy. But you'll have to put the wheel openings several inches above the tops of the tires because those wheels will hang out of the quarters by a couple inches. Basically the quarters have to be at least as high above the tires as your maximum suspension travel under compression. Otherwise your quarters and your tires will end up occupying the same space at the same time, and that's no good. They'd look like this...
      [​IMG]

      To go 10" wide in the back and fit the wheels inside the tubs/quarters you'd need a 1/2" spring offset and a quarter lip trim. Which is what I did to run the 18x10's and 295/35/18's on my Duster. Which looks more like this. Although my car is lower now.

      [​IMG]

      [​IMG]
       
    • travism

      travism Well-Known Member

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      Thanks man, did you make a thread on how you did it? that's exactly how I want mine to look
       
    • 72bluNblu

      72bluNblu FABO Gold Member FABO Gold Member

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      My build thread is linked in my signature, but here it is again My "new" '74 Duster- or why I need a project like a hole in the head

      Short story is I use zero arch leaf springs, installed a 1/2" offset hanger kit, and replaced the offset shackles with a set of leaf spring sliders that lowered the car a little more. I also trimmed close to a 1/2" from the quarter lip to clear the 295's. Eventually I'm gonna drop it another 1/2" or so but I have to reshape the "bump" in the outer wheel house before I do that. The 295's use up every bit of the stock wheel tubs.
       
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      • Killer6

        Killer6 Well-Known Member

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        With the slanty? Hmmm, please tell Us more.............................better yet, some pics???????:)
         
      • travism

        travism Well-Known Member

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        Never said I'll do it well :) just have some fun
         
      • Killer6

        Killer6 Well-Known Member

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        That's the most important part of all...:thumbsup:....BTW, check out the posts for rainydayauto's thread about the rear-end for Her ride,....what I left out of that post was
        the fact that the 7.25 I popped the spiders on was subjected to a dozen or more umm...adolescent neutral drops w/the /6 that was in the car before I swapped
        the cammed 'teener into it. Just make sure You keep it full of quality gear-lube 'till You get up to replacing it !!:rolleyes:
         
      • travism

        travism Well-Known Member

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        Alright thanks!
         
      • Mopower71

        Mopower71 Speed Demon

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        325/50-15 will fit with the offset spring hangers. With a little massaging to the wheel well lip so they don't hit.
        You will have to cut off the spring perches and weld new ones on in the correct location.
        If I were to do it again, I would do the spring relocation into the frame. The problem now is my 3" exhaust is in the way.
        I just moved the front of the springs down 1 1/2" so I could use the upper holes on the caltracs, so the rear of the car sits a litle higher.
        20170502_220600.jpg 20170502_220616.jpg 20170502_220600.jpg 20170502_220616.jpg
         
      • Mopower71

        Mopower71 Speed Demon

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        Whill I was under the car, I also moved the left side front spring hanger back about 1/2" to center the rear.
         
      • /sixchall

        /sixchall Well-Known Member

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        Talk about overkill, my 70 Dodge Challenger w/ a SL6, auto. (904) originally came with a 7 1/4 rear end. However at 225K miles as a daily driver, I believe the gear set was 2.76. The spider gears decided to go south, with that I was looking for a replacement. A guy I knew was parting out his big block '71 E-body. So for $55.00 I ended up with an 8 3/4, 742 case w/ a 3.23 gear set. 11"x 2 1/2",brakes and finned drums,a single legger. W/ 1 3/4 pinion. Cut and rebalanced driveline. Overkill! Ya think?
         
      • 72bluNblu

        72bluNblu FABO Gold Member FABO Gold Member

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        On a stock Duster/Demon/Dart Sport there's ~13" from the inner wall of the wheel tub to the quarter lip, give or take the factory tolerances. That ignores the springs, with a 1/2" offset the inner wheel tub is the limiting factor but with the stock spring locations you lose a little more than a 1/2" to the springs. A 325/50/15 has a 13" section width. On my car even with the quarter lips trimmed all the way back to the spot welds there's only about 13.5". If the car sits low enough that the tires actually sit inside the quarters you need a 1/2" of clearance to the quarter alone. Those 325's work for the same reason the N50's on diymirages car worked, the back of the car is high enough that the suspension travel never puts the tire inside the wheel tub or quarter. Those tires will not fit inside the wheel tub without rubbing. Meaning, if you lowered the car an inch from where you're at now they'd rub like crazy. Sure, they're on the car and they probably don't rub at your current ride height, but, that doesn't mean they actually fit. I can put 35x12.50x15's on a Duster if they don't actually have to fit inside the wheel tubs, piece of cake.

        Taadaa! They fit! :rolleyes:
        [​IMG]
         
      • diymirage

        diymirage HP@idle > hondaHP@redline

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        did you mean the gold 74 (demon clone) or the orange 71?

        because i will sell you those 14X10s and toss the N50s in for free (just pay separate shipping and handling)

        :thumbsup:
         
      • David W

        David W Well-Known Member

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        My 70 swinger with a slant 6 .... i swap in a 8.25 from a 73 duster ( i think ) but it when right in with a set of 8.75 shock plates and new u bolts
        But here what i didnt know ... YOU NEED TO SWAP OVER YOU E BRAKE CABLES .. PULL THE ONES OFF YOU 7.25 and put them into the 8.25 ..
        Or it just be me :D
         
      • halifaxhops

        halifaxhops It's going to get stupid around here! FABO Gold Member

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        I have a drive shaft if needed for a 904 and 8.25 and am just N of you. You can have it for a beer!
         
      • travism

        travism Well-Known Member

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        I probably wont need one for awile, but I appreciate it! finally found someone else from central pa
         
      • halifaxhops

        halifaxhops It's going to get stupid around here! FABO Gold Member

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        Stop by any time usually something going on here. Just shoot me a pm. If needed I have a lift for a fast rear change!
         
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