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Tech: 9" Ford Axle Measurements:

Discussion in 'The Hokey Ass Message Board' started by Drive Em, Apr 3, 2008.

  1. Drive Em
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    Drive Em Member

    I see alot of questions and posts about measuring for axles on a 9" Ford. Since I build these everyday, I figured I would pass along some tips on how to measure for axle width.

    There are a couple of terms that are needed when measuring:

    Total width-this is the total width of the assembled rear end measured from the outside of one axle flange to the outside of the other. Backing plate to backing plate means nothing when measuring for a rear end so forget about that way of measuring.

    Housing width-is the total width of the housing from the outside of the housing on one side to the outside on the other.

    Centered pinion- to have a centered pinion, the left axle has to be 4" shorter than the right axle in all cases.

    Brake offset-this is the measurement from the outside of the axle flange to the edge of the bearing retainer plate that bolts to the housing. Large bearing 9" housings have a 2 3/8" brake offset, and small bearing 9" housings have a 2 1/2" brake offset. There are also others such as 2" and 2 1/4", but you better have the drums and backing plates that go with those offsets or you could be in trouble as far as finding brakes to fit.

    Space between the axles- this is the space between the left and right axles when the axles are bolted in the housing, which is 1.125" for all 9" rears whether you have a locker, spool, posi or open diff.

    So lets figure out the axle lengths on a 58" total width big bearing 9".

    First we divide the 58" total width by 2.
    58/2= 29

    Next we subtract half of 1.125(space between the axles) from 29".
    29"-.562"= 28.438"

    Now we take 28.438", and because the right side axle is longer, we add 2" to that length.
    28.438"+2"=30.438"

    Our right side axle length is 30.438"

    We do the same with the left axle, except we subtract 2" from the length.
    28.438"-2" = 26.438"

    Our right side axle length is 26.438".

    We can check to see if everything is correct by adding everyting together.

    30.438"-right side axle length
    26.438"-left side axle length
    + 1.125"-space between the axles
    =58"- which was our total width to start with

    We can figure the housing width by taking the total width and subtracting the brake offset x 2.

    The housing is a big bearing housing, so the brake offset is 2 3/8".

    We need to subtract the brake offset from each side, so we multiply times two.

    2 3/8" x 2 = 4.750"

    58"-total rear end width
    - 4.750"-brake offset x 2
    =53.750"-housing width

    You can use these formulas to figure your axle lengths and housing widths as long as you know the total width. In the next post, I'll show you how to narrow a housing.
  2. 34toddster
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    34toddster
    ALLIANCE MEMBER

    Good info thanks DE
  3. 65 impala
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    65 impala Member

    good info was a little rusty on it.
  4. fish3495
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    fish3495 Member

    Keep going, I'm shortening one in a couple of weeks.

    Thanks
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  5. Kerry
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    Kerry Member
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    That is indeed what I was asking for in another post. Thanks!
  6. rstanberry
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    rstanberry Member

    how bout some info on adjustments?? i.e. taking out some of the slop in the pinion. can this be done on a used (junk yard) rear or does it need to be rebuilt?
  7. Prop Strike
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    Prop Strike Member

    Good info. Thanks
  8. timmy t
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    timmy t Member

    Does the same hold true with an 8 in.
  9. Scott
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    Scott Member

    Does that mean the pumpkin is centered? if not what is the difference between center pumpkin and center pinion?
  10. sufoowt
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    sufoowt Member

    Drive em isn't 58 - 4.750 = 53.250 or did I miss something? (ps thanks for all the great info)
    Scott If you look at the "pumpkin" from the yoke end you will see that the pinion is offset to one side 2 inches. Thus 2 different axle length if you want the pinion centered. If you want the housing to look centered from the back the axles will be the same length but the pinion will be off center. Both ways work just depends on what you are looking for or have to work with.
    Fred
  11. Iceberg460
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    Iceberg460 Member

    Great info Drive Em!!
  12. Drive Em
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    Drive Em Member

    My mistake, I corrected it above.
  13. CalGasser
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    CalGasser Member

    I have an early housing (round back) with big bearing. Can you recommend someone for some backing plate and large brakes?
  14. Drive Em
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    Drive Em Member

    The big bearing early housing has the large (1/2")mounting holes, so any later model big bearing/big mounting hole backing plates should work, as long as the brake offset is the same. The later brake offset is 2 3/8".
  15. therecruiter
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    therecruiter Member

  16. dirtbag13
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    dirtbag13 Member

    good info !
  17. Retro Jim
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    Retro Jim Member

  18. Retro Jim
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    Retro Jim Member

    Thanks for the great information ! That will really help when ordering new axles !
  19. Larry T
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    Larry T Member

    Attached Files:

  20. therecruiter
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    therecruiter Member

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  21. mechanic58
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    mechanic58 Member

    Here's another handy tip - the pinion on a 9" Ford is offset approximately .970" from the centerline of the third member. That equates to about 31/32". This measurement comes in handy when you're narrowing a housing and you need to have the pinion centered.

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