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Old 04-03-2008, 11:19 AM   #1
Drive Em
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Default Tech: 9" Ford Axle Measurements:

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.

Last edited by Drive Em; 04-09-2008 at 04:00 PM. Reason: mistake
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Old 04-03-2008, 11:35 AM   #2
34toddster
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Default Re: Tech: 9" Ford Axle Measurements:

Good info thanks DE
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Old 04-03-2008, 11:44 AM   #3
65 impala
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Default Re: Tech: 9" Ford Axle Measurements:

good info was a little rusty on it.
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Old 04-03-2008, 11:57 AM   #4
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Default Re: Tech: 9" Ford Axle Measurements:

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

Thanks
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Old 04-03-2008, 12:04 PM   #5
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Default Re: Tech: 9" Ford Axle Measurements:

That is indeed what I was asking for in another post. Thanks!
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Old 04-03-2008, 05:17 PM   #6
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Default Re: Tech: 9" Ford Axle Measurements:

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?
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Old 04-03-2008, 05:23 PM   #7
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Default Re: Tech: 9" Ford Axle Measurements:

Good info. Thanks
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Old 04-07-2008, 10:16 PM   #8
timmy t
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Default Re: Tech: 9" Ford Axle Measurements:

Does the same hold true with an 8 in.
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Old 04-07-2008, 10:54 PM   #9
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Default Re: Tech: 9" Ford Axle Measurements:

Does that mean the pumpkin is centered? if not what is the difference between center pumpkin and center pinion?
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Old 04-09-2008, 01:55 PM   #10
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Default Re: Tech: 9" Ford Axle Measurements:

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
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Old 04-09-2008, 02:55 PM   #11
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Default Re: Tech: 9" Ford Axle Measurements:

Great info Drive Em!!
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Old 04-09-2008, 03:59 PM   #12
Drive Em
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Default Re: Tech: 9" Ford Axle Measurements:

Quote:
Originally Posted by sufoowt View Post
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
My mistake, I corrected it above.
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Old 04-09-2008, 04:06 PM   #13
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Default Re: Tech: 9" Ford Axle Measurements:

I have an early housing (round back) with big bearing. Can you recommend someone for some backing plate and large brakes?
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Old 04-09-2008, 04:30 PM   #14
Drive Em
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Default Re: Tech: 9" Ford Axle Measurements:

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".
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Old 07-26-2009, 08:19 AM   #15
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Default Re: Tech: 9" Ford Axle Measurements:

THIS IS THE MOST IMPORTAN INFORMATION FOR NARROW A FORD 9" THANKS
DRIVE EM

AND THE SECOND MOST IMPORTAN is...
http://www.jalopyjournal.com/forum/s...d.php?t=124310

if you looking to avoid buying a 300+ jig
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Old 07-26-2009, 08:37 AM   #16
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Default Re: Tech: 9" Ford Axle Measurements:

good info !
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Old 07-26-2009, 09:53 AM   #17
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Default Re: Tech: 9" Ford Axle Measurements:

AND THE SECOND MOST IMPORTAN is...
http://www.jalopyjournal.com/forum/s...d.php?t=124310

if you looking to avoid buying a 300+ jig[/QUOTE]
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Old 07-26-2009, 09:56 AM   #18
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Default Re: Tech: 9" Ford Axle Measurements:

Thanks for the great information ! That will really help when ordering new axles !
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Old 07-26-2009, 12:22 PM   #19
Larry T
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Default Re: Tech: 9" Ford Axle Measurements:

[QUOTE=Retro Jim;4158138....... if you looking to avoid buying a 300+ jig[/QUOTE]

Ya really don't have to buy a high dollar jig. We needed to narrow an 8 3/4 rearend about 20 years ago and used a piece of 1 1/4" barstock I had laying around. The guy that needed the rearend narrowed was a machinest and turned out the plugs for it. Next someone wanted to do a 9" Ford. I loaned him the jig, he had the plugs made to fit a 9" and brought it all back when he was finished. Same deal with a 12 bolt and 10 bolt Chevy. You'd be suprised how many rearends use the same sized bearings. Anyway, I need to do "one more" rearend. So I went and repo'ed it from the last guy that borrowed it. Kinda needs cleaned up and checked (rolled on the floor to see if it's still straight) and here we go again.
Larry T
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Old 08-04-2009, 10:26 PM   #20
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Default Re: Tech: 9" Ford Axle Measurements:

Quote:
Originally Posted by Retro Jim View Post
AND THE SECOND MOST IMPORTAN is...
http://www.jalopyjournal.com/forum/s...d.php?t=124310

if you looking to avoid buying a 300+ jig
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That's why you pay a Pro to do it and it won't cost you that much either ![/QUOTE]


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