Im seriously thinking about swapping out my 8.25 for a brand new 9.25 with 3.92 gears for two reasons. first, I have serious plans for a 408 in the future so i'll need to change the rear anyway, and 2nd i want to improve gas mileage with my 3.9 since i do mainly city driving, and i do go to the track often and 17.4's are slow. does anyone know how much a new rear costs and where to get it?

 

Why do you want to spend $1500+ on a brand new axle? I'd just pick up the rear axle out of a dak/durango from a junkyard.

 

Truth. Go to a junkyard and find an axle. The 9.25's have 12 bolts on the cover, the 8.25's have 10. Also, the 8.25's are in like a circle shape, and the 9.25's are like a stop sign shape. That's how you tell the difference. You may or may not be able to find the combo that you want, though (i'm assuming 9.25 with 3.92 and a posi?) You might have to swap the gears yourself.

 

i had the gears swapped out in my 05 dak went from 3.55 to a 4.10 big difference. truck came with the 12 bolt corporate so the swap was simple. $430.00 for the gears and the install. cant beat the price.

 

Swap to something besides a 9.25 diff

A 9.25 diff might live for a few months behind a 408
but the pinion bearings of the 9.25 can't handle high torque
for very long.

Swap to a 3-pinion bearing Ford 9 inch
or a Dana 60 (IH Scouts or mid-80s 250 Rams)
or one of the GM designs that American Axle is now building for the Dodge Rams.

 

because when i'd rather spend money on something i know doesnt have anything wrong with it already. it's going to be behind a 408, im pretty sure a junkyard axle wouldnt hold up very long, plus i want to make sure i get the rear end with exactly what i want in it. im thinking about getting a dana instead of the 9.25, it probably would hold up better. does anyone know how much they cost for a new one?

 

It's not going to be cheap. New D60 housing is going to be $900, plus ~$450 for axle shafts and bearings, ~$700+ for a pair of brakes, ~$700 for a detroit locker, ~$250+ for the ring/pinion, etc., if you piecemeal it together. You could probably get a low-end complete axle for maybe $2500.

9.25" axles are plenty strong enough for a NA 408 on a street vehicle.

 

yea, i think the 9.25 will be strong enough now that i think about it. I'd like to find one out of a junkyard and take it apart and see what kind of shape it's in. If i could find one from a wrecked R/T dak that would be great since it already has the 3,92's and limited slip.

 

put a rear end from a 1972 vw bug

 

i'll get right on that