8 3/4 backing plates onto a small bolt with upgraded big bolt shafts

Brakes for your Classic Mopar

  1. Bronze Barracuda

    Bronze Barracuda Well-Known Member

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    Ok so I've got an original a body 8 3/4 rear end to bolt up to my 68 Barracuda. So I'm changing axle shafts to the big bolt pattern from Dr. Diff when he gets some new ones in. Question do I need to upgrade the backing plates? If so to what size? Also do I need the flat iron bars that go inbetween the front and rear shoe of the rear brakes? Disc will be up front.
     
  2. Dana67Dart

    Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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    Ask Dr diff if the axles are made to B,E body bearing offset or A body offset. That will be your deciding factor.

    Also the A body brakes would have SBP holes in the drums.
     
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    • Professor Fate

      Professor Fate Push the button, Max...

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      If the axles are built to take the B/C/E flange offset, you'll need the corresponding B/C/E backing plates, hardware and drums. 10 or 11 inch.
       
    • Mtrhead

      Mtrhead Ace of Spades ♠️

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      If axles are Yukon they will take small bolt plates ..and predrilled drums
       
    • Professor Fate

      Professor Fate Push the button, Max...

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      SOME Yukons, not all- they offer them both ways.
       
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      • Mtrhead

        Mtrhead Ace of Spades ♠️

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        10-4 ok didn't know they had both
         
      • Bronze Barracuda

        Bronze Barracuda Well-Known Member

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        Ok thanks for the quick replies. So if the axle shafts I get are ,"a body flange offset". Another thought popped into my head, is it possible to find 10 inch drums in the big bolt pattern?

        Just a thought as to where my head was at before I started this thread.
        I was thinking that if I started with a factory a body 8 3/4 rear end (obviously the small bolt pattern) and all I did was swap the axle shafts to a shaft that has the big bolt pattern nothing changes. But then I remembered from somewhere in the dark recess of my brain, I vaguely remember something about needing new backing plates. Maybe because I wouldn't be able to find 10 inch drums in a small bolt pattern.

        PS
        Just to clear things up as I am not sure if all a bodies that came with the 8 3/4 had 10 x 1.75 brakes like mine does.
         
      • 72bluNblu

        72bluNblu FABO Gold Member FABO Gold Member

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        B87E8CDA-4826-4290-8E9E-7915B82FF6B5.jpeg

        BBP axles have a different flange offset than SBP axles. So if you use BBP axles with a standard BBP flange offset, you need new backing plates and drums (10x2.5”).

        If you use BBP axles that have the SBP flange offset, like the Yukon’s, then you have to use the SBP 10x1.75” backing plates and drums and you have to have the SBP drums drilled for the 5x4.5” pattern.

        The backing plate offsets are different as well, you can’t mix and match backing plates and drums.

        It is far easier to use standard BBP axles and upgrade to the BBP 10x2.5” drums, the parts are far easier to get ahold of and usually cheaper. And you don’t need to have anything drilled or changed, everything is off the shelf.
         
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        • Professor Fate

          Professor Fate Push the button, Max...

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          They never put 9" brakes on an 8.75, and 11" were never offered in small bolt pattern. 10" is what you got with an A body 8.75.
           
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          • Professor Fate

            Professor Fate Push the button, Max...

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            There is nothing to decide about the brakes. You said you ordered from Doctor Diff.
            This is from the axle product page on his website:
            upload_2021-11-22_15-39-38.png
            You need different (B/C/E etc.) backing plates, hardware and drums as I noted above. Get them as a set, there were some different widths over the years and each width used it's own backing plate and drum. NO mixing and matching.
             
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            • cudamark

              cudamark Well-Known Member

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              if you're going with the 4 1/2" bolt pattern, make sure you get a set of brakes that match. If you decide to use the 10 X 2 1/2", get backing plates, shoes, hardware, wheel cylinders, and drums for that application. Same goes if you decide on the 11" brakes. They made different widths of brakes in both the 10" and 11". The individual parts need to match or things don't work right.
               
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              • cudamark

                cudamark Well-Known Member

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                Looks like the Professor answered a hair before me! :lol:
                 
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                • Bronze Barracuda

                  Bronze Barracuda Well-Known Member

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                  OK things are a lot clearer now.
                  One other caveat, I've located a set of backing plates that are 11 inch. But here's the other sadly and uniquely Canadian thing. I found out this summer when swapping an 8 3/4 out of a 68 Dodge (unknown model) that it came with 11 x 2 inch shoes. Let me tell you they are ridiculously difficult to find.
                  So one more question is there a way to check that these backing plates I found are not for the 11 x 2 inch shoes?

                  Edit.
                  PS the 68 Dodge 8 3/4 went into my son's 56 Custom Royal
                   
                • 72bluNblu

                  72bluNblu FABO Gold Member FABO Gold Member

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                  Yes, you can determine just from the backing plate if your 11” backing plate is for a 2”, 2.5”, or 3” drum. The offset on those plates is different, and can be measured using the process I describe in this thread
                  Converting rear drum brakes from SBP to BBP

                  The measurements for the plates are there too
                   
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                  • cudamark

                    cudamark Well-Known Member

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                    The '65-71 1/2 ton Dodge PU's used the 11 X 2" brakes as well as a few low end '65-75 C-bodies. Unless you have other known backing plates to compare them with, the only way will probably be to take them to the auto parts store and trial fit shoes against them to see where they hit the top pin and if they line up straight with the wheel cylinder push rods.
                     
                  • Professor Fate

                    Professor Fate Push the button, Max...

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                    RockAuto. Raybestos #334PG $39.79
                    1968 DODGE MONACO 6.3L 383cid V8 Brake Shoe | RockAuto
                     
                  • cudamark

                    cudamark Well-Known Member

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                    Oreilly's has them too..........$32 a set.
                     
                  • SGBARRACUDA

                    SGBARRACUDA ROY FABO Gold Member Legendary Member

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                    Here is a complete parts list you need from Rock Auto.
                    Here is a parts list from Rock Auto
                    Raybestos brake shoes 334PK
                    " Hardware kit H7134
                    " Self adjuster kits H2534 & H 2535
                    " Wheel cylinders WC37053 x 2
                    " Brake Drums 2955R x 2
                     
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                    • Bronze Barracuda

                      Bronze Barracuda Well-Known Member

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                      Yep those are 11 x 2.5 inch or 11 x 3 inch.
                      But no 11 x 2 inch. Luckily the backing plates I picked up 1/2 hour ago are 11 x 3 inch. A little big I suppose for an a body. But better than nothing!
                       
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                      • Bronze Barracuda

                        Bronze Barracuda Well-Known Member

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                        Ok I picked up the backing plates about a 1/2 hour ago. They are for 11 x 3 inch shoes. Seems a bit huge for an a body? I'll probably have to play around with an adjustable brake valve?
                         
                      • Professor Fate

                        Professor Fate Push the button, Max...

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                        upload_2021-11-22_20-31-18.png
                         
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                        • Bronze Barracuda

                          Bronze Barracuda Well-Known Member

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                        • Bronze Barracuda

                          Bronze Barracuda Well-Known Member

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                          Ok here are some pictures of what I just bought. The guy said they were 11 x 3 but I think they are 12 x 3

                          For reference the wheel cylinder part number is Bendix 2227383

                          The only number I could get off the shoes was 323173

                          Pictures to follow.
                          Wasn't exactly sure where to measure the backing plates.
                          Apologies for the picture of the front of the backing plate I was trying to line it up with the groove that goes around the plate. The back side rear s measured more accurately it is from outside to outside

                          PXL_20211123_025157582.jpg

                          PXL_20211123_025214169.jpg

                          PXL_20211123_025241394.jpg

                          PXL_20211123_025457129.jpg
                           
                        • Bronze Barracuda

                          Bronze Barracuda Well-Known Member

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                          Thank you for that link I used your method and I got 2 inches through the center hole with the plate hanging over the edge of the bench.
                          3 inch for sure.
                           
                        • 72bluNblu

                          72bluNblu FABO Gold Member FABO Gold Member

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                          Those look like 11x3’s. The outside to outside backing plate measurement is about 1” wider than the inside brake drum dimensions. So a backing plate for 11” drums is 12” wide, backing plate for 10” drums is about 11” wide etc.
                           
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