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Thread: Differential Install

  1. #1
    Senior Member
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    Differential Install

    Rear End.jpeg
    Getting prepped to install the rear end. I'm a bit confused as to which bolts to use. As you can see from the pic I've set aside 4 brass colored bolts (2 long & 2 short) for the job. The 2 front mounts are OK since the instruction indicates drilling ⅝" holes to expand the existing holes (B in the pic). Here I will use the long bolts. The rear mounts are the issue (A in the pic). While they are threaded, the two threads on the short bolts don't even come close to screwing into the threads of the mounts.

    I'm lost.

  2. #2
    Senior Member edwardb's Avatar
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    According to my records, the rear mounting bolts are M14-2.0 x 100MM flange head bolts and no nuts. Only threaded into the pre-threaded mounting ears. The fronts are M16-2.0 x 130MM flange head bolts with deformed thread and flanged lock nuts.

    So if you're trying to thread the M16 bolts into the rear mounting ears they're not going to fit. The upper and lower control arms use M16 bolts, so suspect the parts you pictured are for those. Not the diff mount. Check your inventory and parts, you should find the right bolts for the rear diff mounts.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
    Build 3: Mk4 Roadster 20th Anniversary #8674. Sold 09/07/2020. Build Thread and Video. Build 4: Gen 3 Type 65 Coupe #59. Gen 3 Coyote. Legal 03/04/2020. Build Thread and Video
    Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023. Build Thread. Sold 11/9/2023.

  3. #3
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    Thanks Ed. For future reference, what do the numbers for the bolts represent?

  4. #4
    Senior Member edwardb's Avatar
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    M14-2.0 x 100MM:

    M = Metric
    14 = diameter in millimeters (little over 1/2 inch)
    2.0 = thread pitch (course standard)
    100MM = length in millimeters (just under 4 inches)
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
    Build 3: Mk4 Roadster 20th Anniversary #8674. Sold 09/07/2020. Build Thread and Video. Build 4: Gen 3 Type 65 Coupe #59. Gen 3 Coyote. Legal 03/04/2020. Build Thread and Video
    Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023. Build Thread. Sold 11/9/2023.

  5. #5
    Senior Member jrcuz's Avatar
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    Be prepared to shave a small amount off of one of the rear mount bushings to get the bolt to line up and begin to thread. When I installed my 2015 IRS I trimmed the right rear bushing 1/16" or so to be able to get the bolt started.
    JR
    Mk4 complete kit #9059 ordered 1/19/17 delivered 3/23/17, 2015 IRS, Fortes/DART347,TKO 600, hyd clutch, P/S, 12.88 wilwood brakes front and rear, heater/defrost and vintage gauges
    First start and go-cart 4/11/18. Taken To Whitby Motorcars Greensboro, N.C. 2/5/21 for body/paint

  6. #6
    Senior Member CraigS's Avatar
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    Also for reference 16mm bolts are .630 inch. 5/8 bolts are .625 inch. So, if you have a hard time finding 16mm, 5/8 is a substitute.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

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