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Thread: IRS Friction Modifier Amount

  1. #1
    Senior Member VAHokie's Avatar
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    IRS Friction Modifier Amount

    Hey guys, instructions say to put 3-3.5 of the friction modifier in the diff but looking at Ford workshop manual it states 4 oz. What is everyone doing?
    MKIV Complete Kit #9494 l Delivered 1/5/19 l First Start 11/28/20 l First Go-kart 4/11/21 l Carb'd 347 l Mid-shift TKO600 l 3.55 IRS l P/S l Forte Mechanical Throttle Linkage l RT Turn Signal, Drop Trunk l Breeze Upper/Lower Radiator Support, Fan Shroud l Boig Upper/Lower Cool Tubes & Quiet Pipes l 18" FFR Gasser Wheels l Build Thread

  2. #2
    Senior Member Gordon Levy's Avatar
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    4oz.
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  3. #3
    Senior Member edwardb's Avatar
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    Looks like Ford shows a different amount of friction modifier depending on Mustang model. 2.3L/3.7L/5.0L = 4.0 oz. 5.2L V8 GT350 = 3.25 oz. I've always used the full 4.0 oz bottle of Motorcraft Additive Friction Modifier XL-3, PN EST-M2C118-A.
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  4. #4
    Senior Member VAHokie's Avatar
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    Thanks, Gordon and Paul. 4 it is.
    MKIV Complete Kit #9494 l Delivered 1/5/19 l First Start 11/28/20 l First Go-kart 4/11/21 l Carb'd 347 l Mid-shift TKO600 l 3.55 IRS l P/S l Forte Mechanical Throttle Linkage l RT Turn Signal, Drop Trunk l Breeze Upper/Lower Radiator Support, Fan Shroud l Boig Upper/Lower Cool Tubes & Quiet Pipes l 18" FFR Gasser Wheels l Build Thread

  5. #5
    Senior Member Traveller's Avatar
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    I just used 3.5 based on the following from Ford tech support for the IRS rear diff:

    MK4 Complete Kit #9673 | Ordered: 08/07/2019 | Pickup: 08/24/2019
    Gen 2 Coyote, TKO600, IRS, Power Steering, 18" Halibrands, Kirkey Vintage Race Seats, Gas-N Headers and Pipes
    Build Thread: https://thefactoryfiveforum.com/show...IRS-Build-9673

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