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Old 12-05-2006, 05:30 AM
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identifying Mopar 7 1/4 and 8 1/4

How do I tell the difference between a 7 1/4 and an 8 1/4 Mopar rearend? I have two rearends and want/hope to use one of them in my Duster. If they are 7 1/4 I will just have to pass but how do I tell the difference, they both open to the rear correct One has the 5 on 4 1/2 bolt pattern but opens to the rear (8 1/4 ????) Did they make a 7 1/4 with the big bolt pattern? How well will an 8 1/4 hold up behind a 360 if I don't get rough with it? Is an 8 1/4 (small bolt pattern) the same exact rearend as the 8 1/4 (big bolt pattern) just with different bolt pattern?............................there,,,that oughta keep some busy for a while

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Old 12-05-2006, 09:24 AM
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This will keep you busy for awhile:

http://www.hotrod.com/techarticles/axle_rear_end_guide/
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Old 12-05-2006, 09:55 AM
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The 8 1/4" will handle the 360 no problem unless you are launching at 6000 rpm with a 4 speed or are using a transbrake.

I ran an 8 1/4" in my duster with 3.21 gears and a sure grip for years and it survived many a burnout and trip to the drag strip with no damage.

the 7 1/4" will break in short order though.
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Old 12-05-2006, 10:06 AM
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mopar did make a 7 1/4" with the 4.5" bolt pattern for the later disc brake A Bodies and the F-M-J body cars. On this particular axle you will notice that the 3" axle tubes taper down to 2.5" right before the center housing. All 4" bolt pattern 7 1/4"s us a 2.5" tube right out to the backing plates.

Still a weak piece with either bolt pattern (I blew the one in my Mom's car up back in the day with a slant six).

I drew this Illustration a few years back to help Identify Mopar axles.
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Old 12-05-2006, 01:24 PM
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Excellent info guys, thanks a million I knew I could count on you guys I LOVE it here
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