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Ford Performance Traction-LOK Limited Slip IRS Differential - 34 Spline 8.8 in. (15-19 GT, EcoBoost, V6)

Market Price $222.60 You Save 12% ($25.61)
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  • Item 388769

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    Features & Details

    • Put the Power to the Pavement
    • 8.8" IRS Limited Slip Differential
    • Factory OEM Replacement
    • Genuine Ford Racing Part M-4204-M
    • Requires 34 Spline Axles
    • Designed for Use with 3.31, 3.55 & 3.73 Super 8.8" Gear Sets
    • Fits 2015-2019 GT, EcoBoost and V6 Mustangs
    Limited Slip Differential. This Ford Racing 8.8" 34 Spline Traction-LOK Limited Slip Differential is a direct fit replacement for your IRS equipped S550 Mustang. A Limited Slip Differential (LSD) sometimes referred to as a "Posi" will allow both rear wheels to put the power down on the pavement giving you better traction and more impressive burnouts.

    Recommended Upgrade. This Ford Racing Traction LOK Limited Slip IRS Differential was specifically engineered for use with Ford Racing Super 8.8" IRS Gear and Pinion Sets, including 3.31, 3.55 and 3.73 gear ratios. Sold separately. Not for use with 3.15 gears.

    Application. This Ford Racing 8.8" Limited Slip Differential is the same original equipment that came standard on 2015-2019 GT, EcoBoost and V6 Mustangs. It is designed for use with independent rear suspensions (IRS) and requires the use of 34 spline axles.

    Technical Note. This Limited Slip Differential requires 4-ounces of CM-19546-A1 friction modifier with initial fill, it is recommended to use differential installation kit M4210B3.

    Fitment: 2015 2016 2017 2018 2019 Details

    MPN# M-4204-M

    CA Residents: WARNING: Cancer and Reproductive Harm -

    What's in the Box
    • (1) IRS Limited Slip Differential
    Installation Info
    Tech Specs
    Will it fit my Mustang?

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    Questions & Answers (13)

    5 Top Rated Questions

    I have a base model 2016 GT is this all I require to swap my gears from 3.15 to 3.55?

    • Hey Arturo, This differential is actually designed to work with steeper gears it isn't gears themselves. To upgrade to a 3.55 gear for your 15gt you would need item# 389949 which are not only the gears but the differential housing and differential to complete the entire install. Now if you wanted to you could get the ring and pinion separate, item#384402 but you would at least need one of these Ford differentials M-4204-MT or M-4204-M in order to complete the installation. And if you plan on making your mustang a high mileage car you would need a bearing a seals kits with the ring and pinion.

    Helpful (2)

    I'm looking to upgrade my 2015 v6 3:15 gears to 3:73 I know I need the gear and pinion plus this since I have the 3:15, but it says I need a 34 spline axle. does the 3:15 already have the 34 spline axle or do I also need to get that?

    • The Ford Performance Traction-LOK Limited Slip IRS Differential will be a direct drop in, as your axles will be 34 spline from the factory.

    Helpful (1)

    I have a 2017 v6 mustang. I want to move up to 3.73 gears, will this fit with the 3.73 gears for a v6? If not, what will I need to fit the 3.73’s?

    • The Ford Performance Traction - LOK Limited Slip IRS Differential is compatible with 3.73 gear sets.

    Helpful (1)

    I have a 2015 mustang gt AUTO with 3.15s. Will this work with my stock housing ? I want to upgrade to 373’s.

    • Yes, this will allow you to regear for 3.73s from the factory 3.15s. 

    Helpful (0)

    I just had my 2915 mustang gt tuned to run 18 manifold with e85 and 47lbs injectors. Does upgrading to 373’s require retuning??

    • You would not need to retune for steeper gears. However, you will need to have your speedometer recalibrated and we recommend using a handheld tuner to recalibrate the speedometer.

    Helpful (0)
    Post Your Question
    8 More Questions
    Will this differential be able to hold up to 800 hp? 1 answer
    Hey I have a 15 gt 6speed and I think my differential is getting bad it has play in it and bump every Time i let off the clutch. So I'm going to change this out and see . Will this work with my car with 3:31 in it and is it a straight forward install 1 answer
    Hi I think I have a worsen in my car - can I straight swap it for this one? thanks 1 answer
    Will this fit on my 2017 f150 with the 8.8 34 spline rear end 1 answer
    Will this work on a mustang ecoboost that's gonna be converted to 3.55's. 1 answer
    Will this work for ecoboost with 3.31? 1 answer
    Okay so I've done many upgrades to my ecoboost performance wise but I need to get all the power faster to the wheels so I need better gears like the 3:55 ring gear. my question is will this differential fit my ecoboost that comes with the 3:15 ring gear from factory? 1 answer
    I have 2015 V6 with 3.15 gears. From that page, it appears I cant upgrade to 3.55's due to the differential and it says I need this (or the $400-500 ones). But this page says its for the GT and in the 'will this fit my car' it also just says the GT. Is there a different one for the V6, or does this work as well and the page is incorrect? 1 answer

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    Customer Reviews (4) Write a Review

    Overall Rating 5

    out of 5 stars

    Installation Time:Weekend

    Installation Cost:$250-$500

    • Performance Gain 5 5
    • Fit 5 5

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $500-$1000

      September 19, 2018

      Must Buy

      In order to have my set of 3.73 gears installed to replace the stock 3.15, I had to buy this part to fit the bigger gears. Nothing special, but it did the trick for making it fit.


      Year: 2015 Submodel: V6

      Helpful (11)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $250-$500

      April 09, 2018

      Not a Mustang

      I researched for weeks trying to verify fitment on the new F-150 8.8. Nobody could tell me if if would fit in the trucks, not Ford or any other internet retailers. I finally decided to get one and give it a shot, and I'm glad I did. There doesn't seem to be much offered for this new axle but this is a great inexpensive option. It fits with gears 3.31 and up. I installed with a 4.56 and so far it's been awesome.


      Year: 2018 Submodel: GT

      Helpful (17)

    • 5/5

      Installation Time: Full Day

      January 23, 2018

      Worked well for rear ends change

      I have a 2017 Ford Mustang V6 with a 6 speed manual transmission. The car came with 3.15 rear ends, I decided to change them to 3.73s. You cannot use the factory differential (new gears are too big), so I bought this differential, new gear set, bearings kit, and axle seal kit, all from American Muscle. A driveline shop did the install in 1 day. I'm very happy with the results. Had no issues with the parts!


      Year: 2017 Submodel: V6

      Helpful (17)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $250-$500

      October 22, 2015

      Worth every penny

      The process of getting the parts and advice needed to upgrade my gear ratios was priceless. I have total felt the difference in the gears. I am extremely happy with my mod. American Muscle customer for life!


      Year: 2015 Submodel: Ecoboost California

      Helpful (13)

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