Can Small Bolt spindles run Big Bolt rotors?

Brakes for your Classic Mopar

  1. Dingos Garage

    Dingos Garage Member

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    Hello, I have a 75 Duster with Big bolt pattern front drums that Im trying to convert to discs. I have the front suspension (spindles, upper/lower control arms, etc) from a 71 small bolt pattern Dart, is it possible to run big bolt pattern rotors/wheels on this combination of parts? let me know, thank you
     
  2. RustyRatRod

    RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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    With one of the Scarebird kits, yes.
     
  3. Dingos Garage

    Dingos Garage Member

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    which kit? i see they have a lot of different ones
     
  4. dano

    dano Evil Handy Man

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    There are kits that use the drum spindle. SSBC, Baer and Wilwood I beleive make some.
     
  5. 72bluNblu

    72bluNblu FABO Gold Member FABO Gold Member

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    So, a couple of things to note here

    1- A-bodies never came with BBP front drums. So, if you actually have BBP front drums, you probably have spindles from a different car (B/E body)
    2- Your '75 Duster has the more desirable large ball joint upper control arms. You do not want to switch those to the small ball joint UCA's your other set up uses
    3- There's no need to switch the lower control arms, they're the same unless they have sway bar tabs

    By far the easiest thing to do would be to buy a set of reproduction 73+ disk spindles and run factory 73+ disks. You swap out the spindles, get the BBP brakes, and everything still uses factory parts for a '75.

    10.95" Front Disc Brake Kit (Stage 1)

    Looks like the full kit is currently out of stock for some reason, although the disk knuckles show as being available. I'd call DoctorDiff on Monday and ask what the ETA was on the kit.
     
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    • Kern Dog

      Kern Dog FABO Gold Member FABO Gold Member

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      This is proof that these cars are subjected to some strange parts swapping.
      When I converted my '70 Charger to front discs, I saved the 10" drum assemblies and used them on a stunt car that I had. I wanted the big bolt pattern for it to have a wider selection of wheels.
       
    • 72bluNblu

      72bluNblu FABO Gold Member FABO Gold Member

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      Which is exactly why you can’t assume something was factory just because you saw it on a car at a yard 30 years later.

      Not the first time I’ve heard of a BBP drum swap though. The later cars especially are easy to do this with because of the large ball joint UCA’s, you just swap on the B-body spindle and brakes. I guess if you have the parts on hand it’s one thing, but the 73+ BBP disk swap is exactly the same amount of work and you get disks.
       
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      • AndyF

        AndyF Well-Known Member

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        Yes, the spindle on the late model drum brake knuckles is the same as on the disc brake cars. So all you need to do is slide a big bolt pattern rotor on the spindle. You'll have to use a special bracket to mount the caliper though. Doctor Diff has this stuff if you want it although I think a better solution is to just swap on a set of disc brake knuckles.
         
      • RustyRatRod

        RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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        You just have to read through the descriptions. You want the kit for the 4.5 bolt pattern.
         
      • AndyF

        AndyF Well-Known Member

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        Here is how I did it 20 years ago. Late model A body drum knuckles, custom adapter plate, Viper calipers, and 11.75 rotors from a B body. It all bolts together. Worked pretty good too for some wrecking yard engineering.
        AR011a (Large).jpg AR011b (Large).jpg
         
      • 72bluNblu

        72bluNblu FABO Gold Member FABO Gold Member

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        The only issue I see with all of this is that you’re assuming he has late model drum spindles. He said he has BBP drums, which means it’s possible he has pre-‘73 B or E body spindles. Which use different bearings than the 73+ stuff.

        I’m just going off the OP’s post, if he has BBP drums then he doesn’t have A-body drum spindles.
         
      • AndyF

        AndyF Well-Known Member

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        Perhaps, just depends what he has on there. The OP doesn't seem to really know what he has so we'll have to wait until he pulls it apart. The car should have late model A body knuckles on there but someone could've swapped on B body drum brakes.
         
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