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Old 01-18-2017, 05:45 PM
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mjgord51 mjgord51 is offline
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GM-12 Bolt Rear End ?'s

I am looking to change out my 3.73 one legged 3rd member and put in a 3.42 posi unit someday. I ran across this in my Chevy/GMC Truck catalog from Classic Industries and was wondering what they mean by "medium case or large case" I haven't gotten real involved in the change over's specs/info yet but will have to start somewhere. thanks in advance. Marvin
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Old 04-14-2017, 01:49 PM
Fast68Chevy Fast68Chevy is offline
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some axles have different pinion gear placement due to larger or smaller diameter pinion head. taller ratios like 2.21 2.56 2.73 3.40 have larger pinion head so sometimes have to be further away from ring gear in the case,

but theyre all 8.875" and 1.438"

AFAIK all the different series in the truck 12 bolts have the same case.

and i dunno why 3.08 when it was 3.07

and there were 2.21 an 2.56 and 2.73 and 3.40 and some other oddball ones too

i really have never sene option availability for anything more than 4.11 in the truck 12 bolts

not sure from where or how thye get their axle info. doesnt seem accurate correct.
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Last edited by Fast68Chevy; 04-14-2017 at 01:59 PM.
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