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Brake Caliper Spacer and Leverage question

  1. Mar 19, 2011 #1
    This has got my brain tied in a knot. Read https://www.physicsforums.com/showthread.php?t=304215" and felt you folks would have good insights.

    I have pieced together a spindle/hub/rotor combo that would require a 1" thick spacer to work. Using a 1 piece spacer and 10.9 mounting bolts, will this hold? My concerns are bolts shearing or the cast iron spindle snapping from the added leverage, neither of which I want to discover by test drive. Also wondering if it would induce vibrations during braking.

    If OK, then do I need to make the spacer from steel or will 6061 t6 suffice (being lighter and easier to machine).

    Last edited by a moderator: Apr 25, 2017
  2. jcsd
  3. Mar 20, 2011 #2
    Somebody mentioned in yor other thread about the bolts not having a shear load when tightened. So watch out for that. Usually bolts aren't intended to carry shear loads.

    Bending could be a problem, as you say. But where are any bending moments coming from? Once you can identify the source of the load, then you can estimate what it would be. It seems to me that the braking force puts nearly zero bending load on those bolts. Is there any outward (along the wheel's radius) force on the calliper?

    Also nearly no axial load, since the calliper will be floating in that direction. So I'd guess it hardly matters what metal you use as a spacer, from a static load point of view anyway.

    I suspect more serious issues could come up over time, like unusual loads, fatigue, unsafe failure modes, corrosion, etc. What happens if one bolt comes loose? Will the brakes still work? Will the wheel lock up? Etc.

    Oh, if you use aluminium make sure it won't deflect much (or fail!) under the tension of the bolts. Just a basic stress/strain calc.
    Last edited: Mar 20, 2011
  4. Mar 20, 2011 #3

    Ranger Mike

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    i think you will be ok with the bolts..if...there is a recessed non threaded bore in the spindle and the bolt thread area is shorter than the clear bore..in other words the bolt thread does not end at the top of the spindle thread area. Also you need a grade 8 or higher bolt.
    if you have machine shop capability i would machine the spacer to have a shoulder that butts up to the spindle and butts up to the caliper so the spacer would take the rotary load. Do not use aluminum as there is a lot of heat generated during braking and the thermal expansion characteristics of the two materials are different. the bolt would eventually loosen up and you are in trouble..
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