I currently have a 79 Chrysler Cordoba with a mild 360, A999 transmission, and 8.25 rear that has 2.45 gears in it. I'm currently trying to gather further information because my idea is to take the car to a shop to swap out the 2.45s for 3.21 gears for the rear. From what I've been told if I understand correctly, that because of an carrier issue I would probably have to swap out the axle in the rear if I want to go to a lower ratio? I really wouldn't want to do that since the prior owner just installed new springs on the rear and I believe I would need to swap out the springs with the axle as well. Anyways, I'm just trying to get confirmation on this swap and decided on where to go. FWIW, this car is all street and no drag racing.

My experience with the 8.25/8.375 is when going from a 2.45 gearset to ANYTHING lower, a carrier swap is in order. Not a big deal since not too many of those rears were cursed with 2.45 gears. A trip to your local u-pull-it should fix you up for less than $30

Thank you for the response, I'm aware that the carrier would need to be changed. The one response I received is that because of the carrier that the rear axle would need to be changed because of the carrier size in relation to the axle housing size? Your post seems indicate otherwise so I'm just trying to get more clarification since I'm not going to be drag racing this car anyways. Maybe a burnout or too plus more grunt from the stoplights.

I had heard that somewhere before but I don`t believe it to be true. I looked in my 77 parts book and the 8 1/4 housing does not show it being a different part number for any of the other ratios. If it was a special housing for the 2.45 ratio I would think it would have shown up there. Maybe for some reason later years changed I don`t know. If someone has a 79 parts book then they could look it up for you. I have a used 8 1/4 sure grip if you want to try it in there to see.

The carrier is the rotating part that carries the ring gear. When making a big ratio jump it is usually necessary to swap the carrier. This can be open or limited slip.

Pretty much any limited slip differential that came in a Mopar is called a Sure Grip, that's Chrysler Advertising's name.

I have never heard about different axle housings for the 8 1/4. Carriers yes, axle housings no.

This may be your time to put disk brakes on the back. There were many Jeep and Chrysler products with the 8 3/8 and disk brakes.

And yes, I know the front does most of the braking, and that disks can be heavier than drums. But the progressive feel with disk brakes is enough better that I favor disks on all four wheels if you can afford it.

When I slowed the engine in my '64Dog from 2800 to 2300 at my maximum speed, the fuel mileage didn't change by a tenth of a mpg. BUT the noise level in the cab was so much less with fewer rpm that it made the swap worthwhile.

R.

I remember a few years ago someone on here was saying the housing needed to be grinded inside or something like that but I never have run into a issue when I changed from 2.45 open to 4.10 sure grip many years ago.

I'd just find a good used axle assembly and swap it. No need to change springs.

For my 1975 Cordoba, out went the 8.25 and in went a 9.25.

Around here they are very hard to come by anymore.

Yeah, on rears with the low numerical gears there can be casting flash in the housing that the thicker ring gear will hit.

Thank you everyone. I will see what I can come with and decide on. I think my first mod will be fuel injection.