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Ford Performance IRS Ring Gear and Pinion Kit - 3.73 Gears (15-20 All)

Item 384403
Market Price $213.12 You Save 12% ($24.52)
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    Features, Video & Details

    • Ford Racing Quality
    • Strong Forged Construction
    • 3.73 Gear Ratio
    • 8.8" Ring Gear Diameter
    • For Street or Track Use
    • Fits 2015-2020 Mustangs Equipped with IRS

    Review & Installation Video

    Review & Install Video

    Upgrade OEM Gears. Are you looking to upgrade to a stronger set of rear gears? Then look no further than installing a set of genuine Ford Racing Gears in your 2015-2020 S550 Pony. Ford Racing Ring and Pinion Gears are perfect for street, road, and race applications.

    Superior Quality. Manufactured in the USA, these Ford Racing Mustang ring and pinion gears feature a super strong forged construction, CNC cut & lapped gear teeth, and are completed in a black oxide finish to resist corrosion.

    Recommended Upgrade.
    Changing the rear axle gear ratio will throw off the calibration of your Mustangs speedometer, but a Mustang Handheld Tuner is a quick and easy way to fix this issue.

    This 3.73:1 Ratio Ford Racing Ring and Pinion Gear set will fit all 2015-2020 Mustangs equipped with an 8.8" Independent Rear Suspension (IRS), including V6, EcoBoost and GT models. A master bearing kit is recommended by most installers, especially on high mileage vehicles.

    Application Note. These Ford Racing 3.73 gears are not compatible with a 3.15 ratio differential - use differential M-4204-MT or M-4204-M.

    Technical Note. Installation costs will vary, but a good rule of thumb is between $250 and $300. Be sure to work with a reliable shop that you trust for installations.

    Fitment: 2015 2016 2017 2018 2019 2020 Details

    MPN# M-4209-88373A

    CA Residents: WARNING: Cancer and Reproductive Harm -

    What's in the Box
    • (1) Ring gear
    • (1) Pinion gear
    Installation Info
    Tech Specs
    Will it fit my Mustang?
    • Bullitt - 19, 20
    • EcoBoost - 15, 16, 17, 18, 19, 20
    • GT - 15, 16, 17, 18, 19, 20
    • GT350 - 15, 16, 17, 18, 19, 20
    • GT350R - 15, 16, 17, 18, 19, 20
    • GT500 - 20
    • V6 - 15, 16, 17

    These 3.73 gears are not compatible with a 3.15 ratio differential - use differential M-4204-MT or M-4204-M.

      Customer Photos (2) Submit Your Photo

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        Questions & Answers (46)

        5 Top Rated Questions

        I have a 2016 ecoboost 8000 miles What do I need to change gear ratio I think I have 3.35 now I was thinking 3.73 what do you think

        • As long as you do not have the 3.15 gear ratio, all you would need would be the ring and pinion!

        Helpful (2)

        Does a swap to this gear require a tune. I'm currently running cobb's stage 1 tune on my ecoboost.

        • Hello! This will not require a tune to run on your vehicle, however we definitely recommend updating your tune, otherwise the calibration of your speedometer will be off!

        Helpful (2)

        So I have a 2016 ford mustang v6 and was told it has the 3.15 axle ration by the dealer "I bought it new" but it always spins both tires. Never once has only one wheel spun. I was reading the 3.15 ration wasn't limited slip. Is this correct

        • The factory gear ratio would not affect if the vehicle was limited slip or not. You cna give your VIN to a Ford dealer who will be able to tell you if a limited slip was installed, however most modern Mustangs came with a limited slip as standard equipment

        Helpful (2)

        So I will need an entire. Rear career to swap in 3.73 gears over my 3.15s in my 16 v 6 mustang

        • Yes, you will need a new center carrier to put 3.73s in a Mustang that had 3.15s from the factory.

        Helpful (2)

        For a S550 Manual Transmission (3.31 Stock Gear) with the Ford Performance Supercharger 670 HP. What Gear you recommend? 3.55 or 3.73? I read that may be for a Supercharged car are better the 3.55, but i dont know. (I only use the car for fun and 201 meters races, highway revs no matter for me).

        • In your application, the highest we would suggest would be 3.55.

        Helpful (1)
        10 More Questions
        What is better for my 2015 auto gt with 3:15s? 3:55 or 3:73 1 answer
        I have 3.15 gears in my 2015. I want 3.73. I want to know what all i need to do the swap before i tear down. Car has low miles and a supercharger with about 100 miles on it. 1 answer
        will this add horsepower? 1 answer
        I have a 2019 Bullitt, is this compatible? 0 answer
        So what do I need to do a gear swap if I have the base 16 GT with an automatic transmission? It has a 3.15 gear ratio and if I understand right, I have to replace other parts too. 0 answer
        I've seen heard that these gears make whine noise, will this noise normal and will it go away? 1 answer
        I have 3:55 in my 2019 mustang GT manual trans. is it a good idea to change to 3:73? For best acceleration . what dou you recommend? 1 answer
        Hello American Muscle. I have A 2018 MUSTANG GT BASE MODEL do i have to change the differential in order to upgrade to this 3.73 Gears or will it be better to get the 3.55. Would my stock differential work with one of this two options? whats the stock ratio on this cars? Please advice thank you so much! 1 answer
        I do have a tuner. My question is there another way to calibrate the speedo without the expense of another tune switching to these gears 1 answer
        How can i tell what gear ratio i have? I read the 2015-2019 v6 have 3.55 as a option. How can i tell which one i have? 1 answer

          Customer Reviews (15) Write a Review

          Overall Rating 4.7

          out of 5 stars

          Installation Time:Full Day

          Installation Cost:$500-$1000

          • Performance Gain 4.933333 4.9
          • Fit 4.866667 4.9

          • 5/5

            Installation Time: Less than 1 Hour

            April 12, 2019

            Another Great Product

            Incredibly fast shipping, great oem product. Always love doing business with you guys!


            Year: 2015 Submodel: V6

            Helpful (0)

          • 5/5

            Installation Time: Full Day

            November 22, 2018

            Great parts

            100 OEM parts works great fits great best bank for your buck! Recommend Anyone who looks into a gear swap to get the ford performance.


            Year: 2018 Submodel: GT

            Helpful (3)

          • 5/5

            Installation Time: Shop Install

            Installation Cost: $500-$1000

            September 19, 2018

            Pricey, But Great Mod

            Jumping from a 3.15 ratio to this 3.73 is definitely noticeable the second you touch the pedal. Wakes up the engine, and runs about 500-750 RPM higher than before. I can now do things in 4th that I used to could do in 3rd. Install was as much as parts, but well worth it.


            Year: 2015 Submodel: V6

            Helpful (12)

          • 4/5

            Installation Time: Full Day

            September 04, 2018

            Great Product, huge difference

            Car felt completely different after the gears, definitely make some noises here there, but that is what i figured after reading the forums


            Year: 2015 Submodel: GT

            Helpful (9)

          • 5/5

            Installation Time: Shop Install

            Installation Cost: $250-$500

            March 27, 2018

            Manual trans Ecoboost 3.31

            Easily one of the top mods I’ve done to my car. This is a handling car and not used for straight line racing so I’m mostly concerned with responsiveness and agility. I found the car felt somewhat “lazy” with the factory 3.31gears, but with the 3.73’s it’s definitely perked up the car and made the throttle response a bit more bearable (the semantics of the debate are irrelevant, the drive by wire system on these cars doesn’t feel like a traditional throttle cable and that’s effectively what I’m looking to simulate). I have gotten a bit of backlash noise after the swap, I’m not sure if it’s from the gears or just my specific backlash settings. I do know the Ford Racing gears are manufactured differently than the stock gears so they may just be a bit nosier. I’ve gotten used to it, but it’s definitely not for everyone. May just be my experience, but definitely something to keep in mind. Unless you’re an expert, you’ll need to have the pumpkin removed and the gears installed. I spent about $380, but labor costs vary. Luckily I was having the abysmal factory trac-lok limited slip replaced with a more competent clutch type limited slip at the same time, so I knocked out two birds with one stone. You will need to purchase a rebuild kit.


            Year: 2016 Submodel: EcoBoost

            Helpful (16)

          • 5/5

            Installation Time: Shop Install

            February 20, 2018

            Automatic 3.15 to 3.73

            So glad I changed out the gears on my 2017 GT. This really changed the feel of this vehicle. Step on the gas and the rpm’s climb fast. Feel like I am now able to see the real gains from the voodoo intake I purchased last month. Car barks at 65. Love it


            Year: 2017 Submodel: GT

            Helpful (23)

          • 5/5

            Installation Time: Full Day

            February 13, 2018

            2017 3.7l v6

            Crazy acceleration feeling like in a stock 2017 5.0 I have an auto had yo have it put on a dyno so it dident shift funny I I have had mine done and can take off faster than any stock gt also make sure you get the 8.8 rear differential it's on here it's the lok one says it's only for GT but it'll work on all three models install took me for ever yo comeple take your time!!!!!


            Year: 2017 Submodel: V6

            Helpful (17)

          • 5/5

            Installation Time: Full Day

            January 20, 2018

            Very happy with this upgrade

            Vehicle: 2017 Ford Mustang V6. Factory gears: 3.15. Upgrade project: swapping 3.15 for 3.73. I tried 2 shops asking them to get their own parts, and it didn't work. Shop 1 (transmission shop) wasn't able to complete the repair in time, and ordered wrong parts. Shop 2 (local Ford dealer) had no idea I needed a new differential, and then raised the price for the install by Cnd$1,000 or US$800. I said 'no'. I then ordered my own parts from American Muscle (gears, ,new differential, and bearings and half axle kits), and went to a driveline shop in Florida (while I was on vacation). The install went without a hitch. All the required parts were there, supplied by me through American Muscle. No noise from the gears. No problems after the install. I just drove 1200 miles back home from FL with the new 3.73 gears, and I couldn't be happier. Good job, American Muscle.


            Year: 2017 Submodel: V6

            Helpful (25)

          • 5/5

            Installation Time: Afternoon

            October 17, 2017


            excellent product fit well had gears installed bye dealer ..very happy


            Year: 2015 Submodel: GT

            Helpful (14)

          • 5/5

            Installation Time: Afternoon

            September 01, 2017

            GT 350 gears

            What a great mix between street, highway, and strip. Easy installation. Noiseless and strong. Great product.


            Year: 2016 Submodel: GT

            Helpful (14)

          • 3/5

            August 25, 2017

            poor communication

            not happy ..did not know that i had to order bearings and shim kit car is now stuck at the service center till missings parts arrive ..would have been nice to have a heads up that this stuff needed to order seperetly ..not pleased


            Year: 2015 Submodel: GT

            Helpful (48)

          • 5/5

            Installation Time: Full Day

            July 04, 2017

            Make sure to change the chunk

            This is the best mod by far it gives you that pushed back in the seat effect just maybe sure if you change to a bigger gear you will need to change the chunk out


            Year: 2015 Submodel: V6

            Helpful (11)

          • 4/5

            May 28, 2017

            ring gear

            means I have to get 5 pieces for each ger is one kit??


            Year: 2015 Submodel: GT

            Helpful (19)

          • 5/5

            June 10, 2016

            Fast shipping

            All can review on this item is the wonderful service by AM once again. All the shops near me are booked for the next 3 weeks so there not in yet. Thank you AM!


            Year: 2016 Submodel: V6

            Helpful (11)

          • 5/5

            Installation Time: Full Day

            May 02, 2016

            Ford Racing IRS 3.73 Gears Set

            Wow! Coated and hardened as well, this gear set is pristine boxed and packaged well no need to worry about any damage of any kind during shipping comes with crush sleeve and pinion nut. Be sure to take your time during install if you're doing yourself! Follow downloadable instructions for video tutorial tutorials to the T and do not take any shortcuts. Be absolutely sure and double check your backlash and gear mesh markings with either the marking compound that comes with a gear install bearing race and shim kit, if not occasionally I will use regular bearing Grease. Then be amazed what a difference from 3:31 to the 373. Day-to-night difference in acceleration and a lot quicker through each gear definitely going to help in my 8 Mile and quarter mile times, and also get rid of the lag and Bogg that 6 gear has on the highway and eliminate having to shift into 5th to accelerate around someone. I'm definitely going to enjoy this for a long time, I searched and searched for a set of 4.10's but just was unable to find... but anyway I'm extremely happy with the 373 s 4 they're definitely going to save me on gas money and mileage and come to many Smiles per gallon thanks American Muscle your speed eaters and shipping is the best. Ray Ulrich


            Year: 2015 Submodel: GT

            Helpful (20)

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