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Yukon Gear 8.8 in. Duragrip Posi Rear Differential w/ 31 Spline 5 Lug Axles (99-04 GT, Mach 1)

Item 393820
Market Price $846.73 You Save 13% ($110.44)
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$736.29 (kit)

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    Features, Video & Details

    • Put the Power to the Pavement
    • 8.8" Limited Slip Differential
    • Heavy Duty Nodular Case
    • Forged 4320 Internals
    • Yukon 31 Spline 5 Lug Axles Included
    • Fits 1999-2004 GT, Bullitt and Mach 1 w/ an 8.8" Differential Housing

    Review & Installation Video

    Review & Install Video

    Put the Power to the Pavement. Boost the performance and improve the road handling of your New Edge Mustang by upgrading to a Yukon DuraGrip Posi Rear Differential. This kit includes an 8.8in 31 Spline DuraGrip Posi Differential, a pair of 31 spline 5 Lug Axles and all the bearings and shims required for installation. This Yukon kit is ideal for those GT, Bullitt and Mach 1 owners who are looking to upgrade their stock differential and axles for better traction and more impressive burnouts.

    Posi Rear Differential. The DuraGrip Posi Rear Differential features a case constructed from a heavy duty nodular iron and boast forged 4320 steel internals and composite clutches for dependable heavy duty performance and long life.

    31 Spline 5 Lug Axles. Stronger than OEM, Yukon Gear manufactures their 31 spline 5 lug axles from high quality 1541H alloy steel for superior strength. They use a rolled spline process that produces an axle spline that is up to 30% stronger than standard cut splines.

    Durable Alloys. The parts in this Yukon Gear and Axle kit are built from high quality, heat-treated metal alloys for long-term durability. Top quality ensures extended use before needing to replace the parts. This complete axle kit includes everything you need for optimal road handling.

    Application. This Yukon Gear 8.8 in. DuraGrip Posi Rear Differential Upgrade Kit with 31 Spline 5 Lug Axles is designed for 1999 to 2004 GT, Bullitt and Mach 1 Mustangs equipped with a 8.8" rear differential housing.

    Technical Note. 1986-2004 V8 Mustangs came factory equipped with 28 spline axles, except for 2003-2004 SVT Cobras which were 31 spline. You will need to reuse your factory 8.8” gear set, or upgrade to a set of our 8.8" rear gears required for this Limited Slip Differential. No aftermarket gears are included. For normal driving conditions we recommend you use 75W 90 rear gear oil. This will give you the same oil weight as factory. For colder temps or race use try 75w 140.

    Fitment: 1999 2000 2001 2002 2003 2004 Details

    MPN# 393820

    CA Residents: WARNING: Cancer and Reproductive Harm -

    What's in the Box
    • (1) 8.8" Limited Slip Differential
    • (2) 31 Spline 5 Lug Axles
    • Carrier Bearings
    • Carrier Shims
    • Axle Bearings
    • Seals
    • Studs
    Installation Info
    Tech Specs
    Will it fit my Mustang?

      Customer Photos (3) Submit Your Photo

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        Questions & Answers (10)

        5 Top Rated Questions

        Hello, I was wondering what differential fluid to use for this part ? Thanks.

        • We offer friction modifier as well as gear oil, of which I can post below: Item 50377 45003

        Helpful (0)

        Most important question what horse power can the axle conversion handle my stock one is only rated for 400 hp I'm well over that ? Thanks 02 mustang gt 3ed rearend

        Will this kit fit a 99-04 v6 automatic and what changes would I have to make ??

        • Unfortunately, this kit was designed for the GT models with the 8.8 rear end and will not work with the V6 models due to the rear end being 7.5. In order to get this kit to work on the V6 models, you would need to make some modifications which would include converting the rear end to the GT 8.8.

        Helpful (0)

        will the moser c clip eliminator kit work with these axles?

        • These axles will work with Moser C Clip eliminators.

        Helpful (0)

        I'm running a supercharger on my stang and a 28 spline aluminium drive shaft and 3:73 gears and automatic do I need to change the shaft and gears or can I use them thanks.

        • The Yukon Gear 8.8 in. Duragrip Posi Rear Differential with 31 Spline 5 Lug Axles will allow you to reuse your driveshaft and gears.

        Helpful (0)
        Post Your Question
        5 More Questions
        My stock axles has abs, will this not work for me? 1 answer
        Does this come with ALL bearings and seals required for installation? Or do I also need to buy a bearing and seal kit? 1 answer
        Stupid question but would this fit an automatic 2000 Mustang Gt? 1 answer
        Can this kit be used to convert a 99-04 V6 to a 8.8" rear end, assuming I acquire an 8.8" rear end housing? Is the driveshaft connection point the same or will that need to be swapped to one compatible with the 8.8" rear end? If driveshaft needs to be changed which one is going to be compatible with the T5 5-spd in my V6? 1 answer
        So what ratio of ring and pinion are with this differential or do we have to use our own? (2000 v6 Mustang with GT 8.8 in. conversion) 2 answers

          Customer Reviews (11) Write a Review

          Overall Rating 4.5

          out of 5 stars

          Installation Time:Full Day

          Installation Cost:$500-$1000

          • Performance Gain 4.363636 4.4
          • Fit 4.909091 4.9

          • 5/5

            Installation Time: Shop Install

            Installation Cost: $500-$1000

            October 26, 2019

            Awesome value and great upgrade

            I had this kit installed professionally A while back with 3.73s and couldn’t be happier. My local speed shop who did the work said they were impressed with the parts and how complete the kit was. It’s still like new after 5,000 miles.


            Year: 2000 Submodel: GT

            Helpful (0)

          • 4/5

            Installation Time: Afternoon

            December 30, 2018


            great fit and finish. installed it with no issues.


            Year: 2003 Submodel: GT

            Helpful (1)

          • 5/5

            Installation Time: Afternoon

            April 27, 2018

            Super fast delivery and great combo

            This was the perfect compliment to my 4.10 years and drag radial addition. Quality axles and the posi kills over the factory Trak Lock


            Year: 2003 Submodel: Mach 1

            Helpful (5)

          • 5/5

            Installation Time: Afternoon

            February 19, 2018

            Best Value Out There And It Is SOLID !

            This Yukon Gear package might be one of the best values on the market. For $622 you get the best 31 spline axels out there (a $350.00 value) along with a top notch posi spring/clutch diff. (a $500.00 value) and all the installation parts (bearings, shims, seals, ring bolts). All told, you are getting about $1,000 worth of top notch upgrade for $622.00. If you plan to put a set of gears or a new diff in your rear, you should get this outstanding bundle and get yourself set up with a 31 spline rear end. Another thing to keep in mind if you cant decide between a sping/clutch diff. like this Yukon or a Torsen set up like the Eaton TrueTrack... The Yukon spring/clutch can be rebuilt if you torch it later on down the road. If you damage a TrueTack, torsen, your only option is to toss it out. If you like, you can also put heavier sprints into your Yukon diff.


            Year: 2001 Submodel: GT

            Helpful (12)

          • 4/5

            Installation Time: Full Day

            February 08, 2018

            if you are a do it yourself guy

            if you're a do it yourself guy give yourself plenty of time to get it done.. for the bad things there is no e-clipse with the package or no manuals on how to set it your homework before attempting but on the good side my car is a lot more torque.. but all i have to say is good job it fits good and performs well..


            Year: 2001 Submodel: GT

            Helpful (8)

          • 2/5

            Installation Time: Afternoon

            February 06, 2018


            Comes with oem timken bearings which I was surprised and happy about which is why it's 2 stars and not 1. The reason I will not go with this brand again is because at about 1000 miles the spider gears decided that they weren't having it and broke into pieces.


            Year: 2004 Submodel: V6

            Helpful (9)

          • 5/5

            Installation Time: Full Day

            January 30, 2018

            Yukon Install

            Have not had a chance to drive yet but impressed with quality thus far. Can’t wait to drive it. Yukon kit combined with Ford Racing 4.10 gears on my 2003 Mach


            Year: 2003 Submodel: Mach 1

            Helpful (7)

          • 5/5

            Installation Time: Shop Install

            Installation Cost: $500-$1000

            June 24, 2017

            Great buy

            For the price you can't beat it. I had some bad bearings so I decided to upgrade the rearend of my 04 GT. AM customer support was a little slack when I asked them did this kit came with all the bearings for the rearend which it doesn't. But besides that it's a great buy.


            Year: 2004 Submodel: GT

            Helpful (9)

          • 5/5

            Installation Time: Afternoon

            June 23, 2017

            Awesome product

            Just had this installed in my 2003 Mach 1 and I can say this was a great investment! Definitely can tell a huge difference from the stock 28 spline


            Year: 2003 Submodel: Mach 1

            Helpful (9)

          • 5/5

            Installation Time: Full Day

            April 14, 2017

            Much better than Ford LSD

            I installed this in my 99 5spd GT. My factory LSD was shot and so where my axle bearings. I went through slot trying to get rid of clutch chatter. My biggest mistake ever was changing fluid brands. Put only Royal Purple 75-90 and only Ford brand LSD fluid, I put 2 bottles of Ford posi fluid. Car always launches straight with equal wheel spin. I tried everything the Yukon techs told me for months. Nothing worked. I broke it in with R.P. and it was perfect. At 500 miles I swapped in Lucas synthetic.... Mistake! So was conventional oil. Clutch chatter to the point it sounded like gears were chewing themselves. Put R.P. back in and it and it is super quiet.. I recommend a larger diff cover to allow more oil capacity. This posi displaces almost 3/4 of gear oil. I went from 3.23 to 3.73 Ford GT 500 ring and pinion bearing install kit also. Rear end is bulletproof now. I changed oil and inspected everything 5 times. Still looks like new a 2k miles, 10k I have zero issues. This is my D.D. too, still get 20-25 mpg


            Year: 1999 Submodel: GT

            Helpful (10)

          • 5/5

            December 23, 2016

            Yukon kit

            Its a great product. Very well built and heavy duty, also a good deal.


            Year: 2004 Submodel: GT

            Helpful (8)

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