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  1. #1
    VOA Mamba Member
    since 2016
    NY/CT
    ek1's Avatar
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    May 2015
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    Break in for diff and transmission

    My car is getting a new diff (existing one is whining) and a new transmission (existing one has an issue with synchros for 1st gear) replaced under warranty. Are there any specific procedures for breaking them in? I remember seeing something here about a diff years ago, but can't find it.

  2. #2
    Supporting Vendor JonB ~ PartsRack's Avatar
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    Oct 2013
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    Recommend easy-peasy for first 100 or so miles; Moderate next 200-300 ; AVOID WOT runs for first 500 miles.

    Fanatic? Chek your diff oil after 1000 !


    ps: You can drive like hell from Mile 1....but you wont care or see 100k miles on ODO!
    Last edited by JonB ~ PartsRack; 06-04-2021 at 05:05 PM.
    Jon "JonB" Brobst ~~~~:<~ JonB@PartsRack.com


  3. #3
    VOA Member
    since 2020
    Ohio
    Steve M's Avatar
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    I looked into this years ago...I'm no expert, but I'll share what I found. Hopefully it helps.

    One of the major issues with a new differential is how tight it is, but it's by design. New bearings will have a little more preload (i.e. they are tighter) than old bearings. They will loosen up during break in, but until they do, they will generate extra heat. Excessive heat breaks down oil. The differentials in these cars don't hold much oil, so keeping the heat in check should be the #1 priority for the first few heat cycles you put on a new diff. If you are running a differential oil cooler, it would be much less of a concern.

    In general, I've found that companies specializing in differentials will say you need to break in a differential for about 500 miles or so before you go hard on it, but how you put those miles on matters. Stated more bluntly: don't just go on a 500 mile road trip and think you are properly breaking in your new differential. It's all about heat cycles.

    For reference, one heat cycle = warming the differential up to full operating temps (20-30 minutes of driving), and then letting it cool off completely overnight (~6-8 hours).

    The first few heat cycles are where the majority of your heat is going to be generated, so I personally try to keep the first few drives on the shorter end (~20 minutes at moderate speeds). After that, just keep on doing more heat cycles until you get about 10 or so done total. Once that is complete (should be around 250-300 miles or so), everything should be pretty well seated. That's when I'd change the differential oil, and then let 'er rip tater chip.

    The transmission will require about the same...breaking in both at the same time is a good way to do it.

    I wouldn't go more than 500-600 miles on a newly rebuilt transmission or differential before changing the oil, just to make sure any excess metal that is likely to appear during break-in won't keep swimming around in the oil. Neither the transmission nor the differential have oil filters, so any debris generated just keeps getting circulated around. Is it absolutely critical? Probably not, but it certainly doesn't hurt anything.

    That's my $0.02.
    2008 SRT-10 Coupe - Venom Red Metallic w/ White Stripes - 1/4 Mile Passes (YouTube)
    High Flow Cats | Gen 5 Intake Manifold | UDP | HPTuners | 3.55s | MCS | DSS Axles | McLeod RST | 11.027 @ 130.06 (Vid), 1.78 60' (+1,622 ft DA, w/ 3.55s & Hoosier Drag Radials)

  4. #4
    Enthusiast quickster2's Avatar
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    Great advice Steve M. I recommended to change the diff oil at 500 when asked while I was at CAAP. Make sure to utilize the latest factory fill spec. fluid.
    2008 Venom Red Coupe -- Sold moving toward a GEN V.
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