Hi everyone,


I'm a new member here, Monday I picked up a Race Red 2012 Mustang GT Premium. It's got the Brembo package on it, and the previous owner (unknown to me before test driving at the dealer) put on Borla's Axleback exhaust, I'm not sure which one, its loud so I'm guessing it's the ATAK exhaust. Onto my question, I cannot find the rear diff listed anywhere and from what I can find, the stock rear gear is supposed to be 3.31, but I have seen a few places say 3.15. It is a 6spd manual so from what I can tell it has the MT82 transmission. I've modded cars in the past so I'm not a stranger to turning wrenches and the like, however this is the first RWD car I've owned and I know nothing about changing the rear gears.

I want to put 3.55 gears in, but I am not sure how to tell what I have, and how do I go about swapping the rear gears. I read if you are ~30k miles then you should replace the bearings too, my car has 16k miles on it so I don't know if I should be really worried about that. If I don't what could happen? Also does swapping rear gears void a factory warranty? I would appriciate any help, I have been searching all over but cannot find a consistent answer. Even if you guys just link me some reading anything will help.

Thank you.

 

https://themustangsource.com/forums/...n-info-493796/

 

Thanks for posting the thread. I actually found this information while researching the Mustang before I bought one. It's how I shopped around for the right one with the features I wanted installed on it. However my windows sticker does not specify a rear end ratio.

 

Then it would have 3.31's. Otherwise it would state 3.55's or 3.73's as an option.

 

You can always spin one of the rear wheels a full rotation and count the number of times the drive shaft rotates. Turns 3 1/2 times = 3.55.

 

That seems like a lot of work when he can just look at the axle code on the drivers door no?

 

It can b used as a future reference, NO? Plus Mr. Obvious, how do you know it still has the factory gears in it.

 

My diff still has the bar code tag on it showing '3.31'

 

You will not notice much if any difference from 3.31 to 3.55. I just did 3.90's from 3.31 and that is a pretty noticeable change. If you aren't fond of shifting is go with 3.73's. With the 3.90's 1st and second are used up pretty quick. On the highway they are still pretty good for cruising. About 2200 in sixth as opposed to 1850 at 70.