8 1/4 8 3/8

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Well, for starters an 8 1/4" is an actual rear end, and an 8 3/8" doesn't exist :-D (or if there is an 8 3/8" ring gear rear end, it isn't referred to as such.)

Now, if you want to know the difference between an 8 1/4" and an 8 3/4" rear, that's a little more involved.

First of all, the 8 3/4" has a larger ring gear (by 1/2", hence the names). It also has a drop out 3rd member (or carrier), the 8 1/4" does not. There are 3 different carriers for the 8 3/4, designated as either 741, 742, or 489 by the casting number on the 3rd member. Although the 742 and 489 are the strongest, all of the 8 3/4" carriers are stronger than an 8 1/4" rear. More gear sets available too. The 8 1/4" isn't a bad rear end though, they should hold up well behind a mild to moderate small block, especially if there's no racing involved.

Here's a link to some threads with more info...

http://www.mopar1.us/875.html

http://www.mymopar.com/index.php?pid=62

And a pretty picture

moparaxleguide.jpg
 
im talking about 8 3/8 not 8 3/4 i seen it on a 78 van rearend on ebay. he has a pic of the specs sticker and it says 8 3/8.
 
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