Since the 8 3/8 rear is basically a mutated 8 1/4, what could you interchange between the two?

You can use the ring and pinion from any of the truck 8 3/8" rears and most of the "guts", I think the adjusters and one set of bearings are different. There is also a small difference in the later style of casing.

-D.Idiot

Thanks, DI. Would you know if a locker unit for an 8 1/4 would fit in an 8 3/8?

what is an8 3/8. i thought the trucks were 9 1/4

It is a mutated 8 1/4.

This is an A-body 8 1/4" rear that currently resides under my Feather Duster.
The 8 1/4" rear has been used in various Mopar platforms for heavy-heavier duty use. It can be found in A-bodies from 1973-1976, replacing the 8 3/4" HD rear-end, under the big C-bodies behind anything from 318's to 400-2v...in trucks they use a slightly beefier ring and pinion for 'towing & hauling' when measured it comes out to 8 3/8" but can easily be transplanted to any of the other car rear ends. The 8 1/4"/8 3/8" axle has been used in dodge/Plymouth Trucks, Jeep Cherokees, Dakotas, etc...
I've heard there is a difference in the post 1996 models, but I've no access to units to compare. The 9 1/4" rear was used in everything from C-Bodies, to Trucks and vans, this was used for 'Extreme Duty' use like a 440 New Yorker, or say a D-300, it has the octagon 12 bolt rear plate.

You should be able to swap a more modern sure-grip from a truck into an earlier 8 1/4", Mopar Perf used to sell these units in their catalog.

So if you want to drag, and find a 1986 dodge with an 8 1/4" 3.91 sure-grip unit, you should be able to swap with no problem...

good luck,

-D.Idiot

Ok. I found this rear under an old Plymouth van, and it is going to take the place of a 7 1/4 in a friends Duster. Just looking to see if it is worthwhile to stick it under there, and how the market is for parts.