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Thread: 3.91 Diff Upgrade

  1. #1
    Join Date
    Aug 2012
    Location
    Phoenix, AZ
    Posts
    140
    My Cars
    2005 M3 ZCP

    3.91 Diff Upgrade

    I'm looking to do throw a 3.91 in my E46 M3 and trying to figure out all the detail. I'd like to go BMW Motorsport if possible and keep the M Variable LSD. I'm seeing rebuilds on ECS for about $3100 so i'd hope I could be out the door for under $3600.

    If anyone has information on the best places to source and typical shop hours involved for this swap I'd appreciate it.

  2. #2
    Join Date
    Aug 2017
    Location
    Menlo Park
    Posts
    87
    My Cars
    '05 ///M3
    Look at diffsonline.com Dan is very knowledgeable. If anything, just chat with him.

    Sent from my SM-G950U using Tapatalk

  3. #3
    Join Date
    Mar 2011
    Location
    PNW
    Posts
    935
    My Cars
    LS E46
    A simple gear ratio change doesn’t cost that much. That’s the price of a full rebuild and ratio change.

  4. #4
    Join Date
    Aug 2012
    Location
    Phoenix, AZ
    Posts
    140
    My Cars
    2005 M3 ZCP
    Thanks for the input, I spoke to Dan at Diffsonline and the take away was basically the m variable lsd is garbage, so recommended going with a rebuild and a 3 clutch 35/60 ramp.
    That spec comes out to around $5k pre install/labor

    Anyone have guidance on if full rebuild/LSD change is needed or if a simple ring and pinion gearing change will suffice?

    This mod seems super common, but I can't imagine everyone is spending $5-6k. I'm just trying to find the best option that will cover all bases but not be overkill.
    2005 Interlagos M3 ZCP
    - AA Catless Headers, OEM Sect 1 & 2, Status Gruppe SCZA Sect 3, KW V3's, Eventuri Intake, ESS Tune, Auto Solutions SSK, Recaro Sportster CS's, Apex Arc8's -275/35/18 Squared

  5. #5
    Join Date
    Mar 2011
    Location
    PNW
    Posts
    935
    My Cars
    LS E46
    That’s also way too much. Not sure where people are getting these prices from. That’s the cost of a freshly rebuilt 420G transmission. I paid $3k for a 4.10 gearset and a freshly rebuilt E32 4 clutch LSD to be put in my case. I only supplied the case and the stubs.

  6. #6
    Join Date
    Mar 2011
    Location
    PNW
    Posts
    935
    My Cars
    LS E46
    Speed Garageworks in Duvall, WA.

  7. #7
    Join Date
    Jan 2006
    Location
    Cary, NC
    Posts
    409
    My Cars
    2006 M3 Cabriolet
    As another reference point, this was in 2017.

    East Coast Gear Supply, Raleigh NC

    New Ring and Pinion Install $250 Labor only,

    I supplied the new BMW Gear Set (3.91:1), 3 bearing seals, a nut and crush collar.

    They supplied any shims that were required and break in oil.

    They are great folks - turned this around in a few days.

    Mike
    Mike
    Cary, NC

    My Driver
    - 2006 E46 M3 Cabriolet, European Headers and Cats, Supersprint Sport Muffler, 3.91:1 Final Drive, TTFS Tune

    Past Rides
    - 1991 BMW 325i Cabriolet, European Exhaust (w/o Cat), Bilstein Shocks and Struts, Hella Ecode Headlights,
    - 2000 BMW 323i Sport Touring, 330i Front Calipers & Rotors, Bilstein Shocks and Struts, SAP Delete, Sirius Receiver, HID/Projector Headlights.
    - 1994 BMW 325is, S50 Engine, Schrick Cams, Custom Chip, 3.46:1 LSD Final Drive, 330i Front Calipers & Rotors (Lots of Modifications)
    - 1987 BMW 325is European ECU and Camshaft, M3 Suspension, Headers with Custom Exhaust.

  8. #8
    Join Date
    Jun 2021
    Location
    California
    Posts
    2
    My Cars
    2002 BMW M3 E46
    I'm also looking for a diff upgrade.
    Thinking about 4.10 and Quaife, but at diffonline.com this comes out around 5k.. Is there any other reliable source that does online-shopping?

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