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Discussion Starter · #1 ·
I'm having trouble finding the exact rear end numbers for my car. I'm thinking they are 3.15. I am trying to upgrade to 3.73 and American muscle.com says that I cannot unless I buy other parts because it's not compatible. Basically the part they are saying I need it's like almost $1,000. Can someone verify with me if it is 3.15 or something different. Also, what do I need to do to change them out? This is what I was getting, but it says in the description, that it will not work with 3.15 gears.

Ford Performance Mustang 3.73 Ring and Pinion Gear Set - IRS M-4209-88373A (15-17 All) - Free Shipping
 

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you should be able to look at the build sticker on your door jamb..there will be a 2 letter code under rear end. That will give you what to search for. I will caution replacing gears takes experience...don't cheap out with your installer or parts.

Welcome to Mevo

Mud

newbies are xpected to post pictures
 

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There should also be a white sticker on the differential with the gear ratio. Assuming that you bought the car new and the gears have not already been changed. As Mud said, this is not a job for a novice. Look for a shop with a good reputation.


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The year of your car would have been a big help but I'll go on the assumption it's a 2015+ auto with 3.15's.

You cannot just swap gears since the housing is to small that holds the 3.15's. You would need a whole new rear axle, Whipple flare tool, and a host of small parts. Factor in labor if you're not doing yourself you're looking at close to $2000. And then when you've done all that you can come to the conclusion you just spent a boat load of money for 0 performance gain.

Use the search button as I've explained this already many times.
 

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If its a 3.15, then Ford says you can if you install with specific traction lock for that application. They did not mention any other mods/parts. This is one of my many projects i have yet to attack. I'm going 3.55.
 

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If its a 3.15, then Ford says you can if you install with specific traction lock for that application. They did not mention any other mods/parts. This is one of my many projects i have yet to attack. I'm going 3.55.
You have a 2013, he has a 2015. It's not a direct swap for him without changes being made in the PCM and BCM.
 

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Discussion Starter · #7 · (Edited)
Sorry, it is 2016 Mustang V6 manual. I bought it brand new, first owner. So the gears are normal stock. Never been changed. I have a mechanic that is going to do all the work I need to do that is necessary. I am definitely not capable of doing this type of thing. LOL
 

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Discussion Starter · #8 ·
M-4204-M or a M-4203-MT is what American Muscle says I need if I have 3.15 right now. On the website, that is. I have not spoken to them on the phone. They are closed until tomorrow
 

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Discussion Starter · #9 ·
Basically what it's telling me is I need a new differential. Of course, there might be something else I need. One of the options is $980 and the other option is only like $180. And it does say they are for the GT, but at the same time, I seen they were for all models of 2015 through 2017. Obviously I would rather go with the $180 option. But I don't know the difference between the two
 

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Basically what it's telling me is I need a new differential. Of course, there might be something else I need. One of the options is $980 and the other option is only like $180. And it does say they are for the GT, but at the same time, I seen they were for all models of 2015 through 2017. Obviously I would rather go with the $180 option. But I don't know the difference between the two
Did you read my 1st post at all on what was necessary?
 

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You have a 2013, he has a 2015. It's not a direct swap for him without changes being made in the PCM and BCM.
I have a 2015 diff i'm going to install in another car. Traction lock p/n is M-4204-M. Again i have to install in 2015 auto pumpkin, but was told with this p/n (and new ring gear) it would bolt in.
 

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Discussion Starter · #12 ·
Yes I did read what you said. Why would it be a Zero Performance gain? I thought from what I have read and what a few friends told me that when you change that out to a higher one, then it gives you more low-end power. I will have to switch gears more also though.
 

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Discussion Starter · #13 ·
Basically, I bought a Roush cold air intake, a Flowmaster axle back Outlaw exhaust and a Bama tuner that Bama is going to do exactly to all the specs of my car. I also bought aftermarket rims and tires. I was going to do the throttle body, but it's so expensive and I heard it's not worth the money until it really goes down on the price. Because my car is so new, everything is so expensive. Then I was going to do headers, but I plan on installing a supercharger in the next 3 or 4 months. I have to save $6,000. LOL
 

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Discussion Starter · #14 ·
I talked to American Muscle and CJ Pony today and we figured everything out. I ended up going with American Muscle because that's why I got my other parts from and they have been very very kind to help me out. They did verify that M - 4204 - M will work for my car. That is one of the differentials that they were providing for my car. And then I have to just add the 3.73 gears with that. Basically cost me like $413
 

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Don't forget the Whipple flare tool or your car won't run right and go into limp mode.
 

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Yes I did read what you said. Why would it be a Zero Performance gain? I thought from what I have read and what a few friends told me that when you change that out to a higher one, then it gives you more low-end power. I will have to switch gears more also though.
If you go on the General Mustang Discussion Forum that will give you insight about what gears will do for you and won't do for you.
 
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