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Ford Performance Traction - LOK Limited Slip IRS Differential - 34 Spline 8.8 in. (15-17 GT)

Market Price $203.99 You Save 12% ($25.02)
Our Price

$178.97 (each)

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  • Item 388769
  • MPN# M-4204-M

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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 2015-2017 GT 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 GT. 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 2015-2017 GT 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 Details

What's in the Box
  • (1) IRS Limited Slip Differential
Installation Info
Will it fit my Mustang?
  • GT - 15, 16, 17

Customer Photos

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6 Questions / 6 Answers

Ask a Question

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 (1)

Will this fit on my 2017 f150 with the 8.8 34 spline rear end


  • The Ford Performance Traction - LOK Limited Slip IRS Differential is specifically designed to work with the 2015-17 Mustang GT's and will not work properly with your 2017 F-150.


Helpful (0)

Will this work on a mustang ecoboost that's gonna be converted to 3.55's.


  • Yes, this works with 3.31, 3.55 & 3.73 gears.


Helpful (0)

Will this work for ecoboost with 3.31?


  • Unfortunately this will not work on an Ecoboost with the 3.31.


Helpful (0)

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?


  • That differential here is designed specifically for a GT, so if you want to upgrade your gears, you would need to buy the equivalent but for an Ecoboost. You can find this here:


Helpful (0)

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?


  • This part will not work with the V6 model Mustang. You will want to purchase the Ford Performance T2R Torsen Differential - 34 Spline 8.8 in. Item #390234 (


Helpful (0)

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Customer Reviews (1) Write a Review

Overall Rating 5.0

out of 5 stars

Installation Time:Shop Install

Installation Cost:$250-$500

  • Performance Gain 5 5
  • Fit 5 5

  • 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 (1)

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