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Thread: 1972 Sportster Front Hub ID Braking Surface

  1. #1

    Default 1972 Sportster Front Hub ID Braking Surface

    Does anyone know the stock dimension ID for braking surface on the front hub on a 1972 Sportster? I'm measuring right at 8". I'm trying to see if it has some useful life left.

  2. #2

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    At one time and maybe still from the right vendor you could buy O.S. Shoe sets, if your drum is running true round you might use O.S. if you can find them or need them. Assemble the shoes on the backing plate, take some measurements from shoes and compare to drum. I ran that drum/shoe arrangement on a Super Glide for 25 years and never wore out or used up a drum, shoes yes but no drum in those years of riding.

  3. #3
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    Quote Originally Posted by soundnav View Post
    Does anyone know the stock dimension ID for braking surface on the front hub on a 1972 Sportster? I'm measuring right at 8". I'm trying to see if it has some useful life left.
    8 inches. A much bigger deal on these hubs are the spoke holes. Check yours very carefully for cracks and/or unexpectedly loose spokes. To be clear; these will be SINGLE loose spokes -- not multiples like you see if you've hit a bunch of pot holes in a row :-)

    OS shoe sets can still be found -- but be forewarned they were produced by the MoCo before we knew just how deadly asbestos fibers could be. A safer alternative is to simply buy new brake lining material in the thickness you need (stock or OS) or to send the shoes out for relining. Currently, there are a few companies offering performance shoe upgrades . . but they ain't cheap -- https://www.vintagebrake.com/drum.htm

    I do my own -- mostly because it is nowhere near as hard as people say. Basically, if you've already gotten into older bikes and have already joined the AMCA and made your way onto the forum -- you probably are capable enough to figure out how to rivet or bond new shoes . . .

  4. #4
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    Oh, and sorry, I forgot to answer the other half of your question. Generally, a drum would be considered to be reaching its limit when the ID reaches 2/3rds of the OD of a freshly mounted set of shoes. There are "exact" specs for this; but the rule of thumb seems to come awfully close in many instances.

    It's not so much a safety issue from the stand point of braking as it is distortion. With the right "modern" shoes you can extend the life of even a close to worn out drum much longer than you might imagine. Mostly because a good set of woven linings "wicks" heat away in an amazing way -- and because we can use "soft" shoes that don't really tear the drum up further.

    All sorts of ways to cheat AND get better brakes than 1972; but only you will know you cheated :-)

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