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I have a '72 XR7 with factory 9" 2.75 non-locking rear. Door tag says rear axle code "2". I'm hoping someone can tell me if it is a 28 or 31 spline rear gear. Thanks for any help.

M
 

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Contributing Sr Motorhead
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Yours is 28-spline. Trust me.
 

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Not even 351C-4V-4spds got 31-spline! Only big blocks.
 

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Not even 351C-4V-4spds got 31-spline! Only big blocks.
Except in 1969 & 1970 the Boss 302 Eliminators got the 31 spline axles.
 

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Except in 1969 & 1970 the Boss 302 Eliminators got the 31 spline axles.
Point taken... but for 71-73s the post is still valid ( chime in for pre-71 390s X- and S-codes) or if I'm [shudder]<shudder> wrong...) I don't profess to everything! LOL!!!</shudder>
 

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If you do in fact have a 28 spline rear axle, don't worry about it for general all around street use. If set up properly, you'll really have to try and tear it up. 28 spline axles have a scallop that takes up almost the whole axle end that you can see when the wheel is removed. 31's have 3 holes on the end-the middle one being about 1/4" diameter, and to it's side the other 2 are about 3/16". About in there somewhere.
 
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