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Ford Performance IRS Loaded Differential Housing 3.55 (15-17 GT, V6)

Market Price $1,049.00 You Save 14% ($150.00)
Our Price

$899.00

+ $99.00 Handling Fee with FREE Shipping
  • Item 389949
  • MPN# M-4001-88355

In Stock Ships same business day. Choose options to add to cart

Features & Details

  • Original Equipment on Manual GT Mustangs
  • Iron Housing with Aluminum Cover
  • 8.8" LOK Limited Slip Differential
  • Pre-Loaded with 3.55 Gears
  • Requires 34 Spline Axles
  • Genuine Ford Racing Part - M-4001-88355
  • 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
Original Equipment on Manual GT. When the light turns green, allow your V6 or GT S550 to accelerate off the line faster by installing a Ford Racing 3.55 Differential. This Ford Racing 3.55 IRS Differential Housing improves the low end torque of your Mustang for stronger, quicker launches. So whether you want to upgrade your gears or replace a broken housing, you can't go wrong with a direct fit replacement differential that was standard on manual GT Mustangs from the factory. This fact makes the manual iron differential the perfect upgrade replacement for automatic Mustangs that see a lot of track time.

Pre-Loaded. Ford Racing pre-installs a set of their 3.55 ratio gears and a LOK Limited Slip Differential into an iron IRS housing and tops it all off with an aluminum cover. This LSD is ready to be installed straight out of the box.

Traction-LOK Limited Slip Differential. The included heavy duty Ford Racing Traction-LOK Limited Slip Differential (LSD), sometimes referred to as a "Posi", allows both rear wheels to put the power down to the pavement as needed. If one of the drive wheels begins to slip or lose traction, the LSD transfers more power to the nonslipping wheel to provide better traction to keep you moving. This makes Limited-slip Differentials ideal for street, autocrossing, road racing and impressive burnouts.

Ford Racing 3.55.1 Gears. The pre-loaded Ford Racing ring and pinion gears have a 3.55:1 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 3.55 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 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 3.55 Loaded IRS Differential Housing is a direct fit upgrade replacement for the 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.

Most Helpful Reviews

5/5
BIG DIFFERENCE!!

When I purchased the Ford Performance Differential with 3.55 gearing to replace the 3.31 that came with my 2016 GT/CS, I was a little nervous...but after the exchange, I noticed quite a difference right ...

Read More
Helpful (1)

5/5
3.55

This did the job perfectly just as advertised. Buddy and I installed this ourselves couldn't be happier.

Helpful (1)

Overall Rating 5 out of 5 stars
Read All 3 Reviews

Customer Photos

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7 Questions / 6 Answers

Ask a Question

I have a 2016 v6 mustang with an automatic transmission, is anything else required for this to fit ??

FERK

  • The only extra component required since the vehicle is automatic is the pinion flange part #M-4851-M8A, however, it will also require reprograming for speedometer correction and, in the automatic transmission, the shift point corrections.

    AMjordan

Helpful (0)

This is a follow up question regarding The Roush tune. I understand the retune is necessary when changing the rear gears for speedometer correction. My question pertains to the shift changes,throttle mapping,etc that the Roush tune does for the car. Will these changes carryover to the new gears in relation to the speedometer/tachometer activity?

KevinP

  • Yes, they would have to be requested from roush when doing the retune but those changes would carryover to the new rear end setup in that car.

    AMjordan

Helpful (0)

I have a dealer installed Roush level one tune on my 2015 V6 which has 3.15 gears on an auto transmission.If I put this 3.55 on my car will the necessary retune keep the shift points the same that the Roush tune intended?

KevinP

  • Yes, the vehicle will have to be retune for 2 reasons; the 1st being that the shift points would want to be changed for accurate performance, and 2, so the speedometer would read the correct speed of the car.

    AMjordan

Helpful (0)

I have an ecoboost mustang which I see isn't listed for this diff. What would stop it from working?

WadeV

  • The Ford Performance IRS Loaded Differential Housing 3.55 will fit Ecoboost Mustangs without any additional upgrades, however we do recommend stronger half shafts for this application, especially if stickier tires are installed.

    Rob D

Helpful (0)

Can I get 3.73 gears put in instead of 3.55's

DonavineM

  • The Ford Performance IRS Loaded Differential Housing comes directly from Ford performance with 3.55, For 3.73's you would want to look at M-4001-88373T Ford Performance IRS Loaded Differential Housing 3.73 Torsen

    Rob D

Helpful (0)

If I install diff in 2016 auto , can I change the driveshaft to Driveshaft Shop manual and not have to change the pinion flange ?

GTJimmey

  • The Ford Performance IRS Loaded Differential Housing 3.55 will come with the manual trans pinion flange, so no pinion flange swap would be needed.

    Rob D

Helpful (0)

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Customer Reviews (3) 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

    March 18, 2017

    BIG DIFFERENCE!!

    When I purchased the Ford Performance Differential with 3.55 gearing to replace the 3.31 that came with my 2016 GT/CS, I was a little nervous...but after the exchange, I noticed quite a difference right away! The car was fast before but not as quick as now. I had a Ford dealership to do it. The guys there are Mustang enthusiast! Cost was around $700. It's been a little more than a week now and I am very satisfied.

    JamesM

    Year: 2016 Submodel: GT

    Helpful (1)

  • 5/5

    October 02, 2016

    3.55

    This did the job perfectly just as advertised. Buddy and I installed this ourselves couldn't be happier.

    Archie

    Year: 2015 Submodel: V6

    Helpful (1)

  • 5/5

    Installation Time: Shop Install

    Installation Cost: $250-$500

    June 29, 2017

    awesome product

    Got this to replace the stock 3.15 gears and aluminum housing and it works beautifully... car takes off quickly

    Grnmnstr

    Year: 2015 Submodel: GT

    Helpful (0)

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