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Ford Performance IRS Loaded Differential Housing 3.73 Torsen (15-17 GT, V6)

Market Price $2,092.97 You Save 13% ($273.00)
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$1,819.97 (each)

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  • Item 389786
  • MPN# M-4001-88373T

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Features, Video & Details

  • Original Equipment on Performance Pack Equipped Mustangs
  • 8.8" T-2 Torsen Differential
  • Pre-Loaded with 3.73:1 Gears
  • Full-Time Torque-Sensing, Torque-Biasing
  • Requires 34 Spline Axles
  • Genuine Ford Racing Part - M-4001-88373T
  • Direct Fit Upgrade - Tune Required for Speedometer and Shift Corrections
  • Automatics will require Pinion Flange Kit part# M-4851-M8A
  • Fits 2015-2017 GT and V6 Mustangs

Review & Installation Video

Review & Install Video

Original Performance Pack Equipment. Improve the low end torque and handling performance of your S550 Pony with a Ford Racing Torsen 3.73 Differential. This Ford Racing 3.73 Torsen IRS Differential Housing is the same exact original equipment that comes standard on Performance Pack equipped Mustangs.

Pre-Loaded. Ford Racing pre-installs a set of their 3.73 ratio gears and a T-2 Torsen differential into an iron IRS housing and tops it all off with an aluminum cover, so it's ready to install straight out of the box.

Ford Racing T-2 Torsen Differential. The included heavy duty Ford Racing T-2R Torsen 8.8" differential uses a worm gear friction system that features full-time torque-sensing and torque-biasing for maximize performance. Torque Sensing keeps power going to the ground during changing traction conditions, while Torque Bias factors how much torque the differential can send to the wheels depending on the available traction. This Torsen design is far superior to standard limited-slip differentials making it ideal for street, autocrossing, and road racing.

Ford Racing 3.73.1 Gears. The pre-loaded Ford Racing ring and pinion gears have a 3.73:1 gear ratio and 8.8" ring gear diameter. These gears are manufactured in the USA and feature a super strong forged construction with CNC cut & lapped gear teeth. They are completed in a black oxide finish for corrosion resistance.

Required Upgrade. The Ford Racing 3.73 Torsen IRS Differential will require reprogramming the vehicles computer for speedometer and shift point corrections. AmericanMuscle recommends a Bama custom tune with a Mustang Handheld Tuner to reprogram the vehicles computer (ECU) for proper operation.

Automatic Transmission Requirement. Installation of this Loaded Torsen IRS Differential Housing on a S550 Mustang with an automatic transmission will require the Automatic IRS Pinion Flange Kit part# M-4851-M8A for proper installation.

Application. This Ford Racing 3.73 Loaded Torsen IRS Differential Housing is a direct fit upgrade replacement for 2015 to 2017 GT and V6 Mustangs. Designed for use with independent rear suspensions (IRS) and requires the use of 34 spline axles.

Fitment: 2015 2016 2017 Details

What's in the Box
  • (1) Loaded IRS Differential Housing
Installation Info
Will it fit my Mustang?
  • V6 - 15, 16, 17
  • GT - 15, 16, 17

Automatics will require Pinion Flange Kit part# M-4851-M8A for proper installation.

Customer Photos

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9 Questions / 5 Answers

Ask a Question

I have 2015 V6 to l have 34 spline axle???


  • Yes, your 2015 V6 Mustang has 34 spline axles.


Helpful (1)

What's the difference between this Torsen differential and just the standard differential with 3.73 gears?


  • The Torsen T2 differential uses torque-sensing and torque-biasing technology used standard in the performance pack mustangs as well as the GT350 mustangs. The standard LSD in the GT mustangs is a simple clutch pack within the diff to help with separate wheel speeds.


Helpful (0)

How does this impact mileage and highway RPM's/noise? I have the 3.15 tear end in my '15 GT.


  • The Ford Performance IRS Loaded Differential Housing 3.73 Torsen will increase the highway RPM's in your Mustang, typically putting you in the range of around 2100-2200rpm at around 60mph in 6th gear. You may notice slightly more exhaust noise due to the higher RPMs

    Rob D

Helpful (0)

Need to install the Pinion Flange Kit part# M-4851-M8A to convert to automatic - where installation requires Special Service Tool: 205-233 (T85T-4851-AH) Installer, Drive Pinion Flange. How can I install the pinon flange without the tool?


  • Installation of the Pinion Flange kit requires the use of the Drive Pinion Flange Holding Fixture. It cannot be installed properly without. We do not carry either product, unfortunately, and recommend contacting Ford directly for more specifics.


Helpful (0)

What is the average install time for the differential?


  • Installation information, including installation time, can be found in the "Installation Info" section of the item page.


Helpful (0)

What is the power rating for IRS?


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Customer Reviews (1) Write a Review

Overall Rating 5.0

out of 5 stars

  • 5/5

    September 09, 2016

    Performance package

    This is what comes with the official mustang gt performance package. Makes my mustang nice and aggressive.


    Year: 2016 Submodel: GT

    Helpful (1)

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