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Half shaft broke!!

Home-org Forums Nuts & Bolts Tinkering Half shaft broke!!

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    • Gear Head
    • ★★★

    Day before yesterday, with my completely stock NC 2013 GT with LSD, turning left aggressively, my driver side half shaft sheared in two at the boot near the diff. 140K, driven hard but no mods. I don’t know if the boot was torn, but I had no warning. Undercarriage has been kept clean and free of rust.

    No noises, no warnings. It looks like the tripod joint pulled away from the socket within the inner boot. Too many burnouts? Could excessive roll cause this? I was turning left pretty hard, is it possible that the driver side wheels approached full droop…?

    The socket or cup that holds the tripod joint is still in my diff. and not attached in any way to the driver side wheel. When I try to drive, the drivetrain spins but I get no wheel movement despite having an LSD. Do I need at least some friction on both wheels to spin them? I think I read this somewhere…

    I have a used replacement on the way.

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    • Pro
    • ★★★★

    Sorry to hear of your mechanical difficulties. Sheering an axle is certainly an unusual situation. The only people I’ve heard of doing that is with super sticky tires on a prepped track and huge power.

    You say you were turning left, that would put the driver’s side (assuming left hand drive) under compression, not droop. But either way the Miata’s suspension is designed to hit the bump stops before it comes apart.I guess if it sheered, then the tripod joint would have the freedom to come apart?

    Good luck with the repairs.

    Dave

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    • Gear Head
    • ★★★

    Thanks Dave, I have a used halfshaft coming.

    Wouldn’t centrifugal force throw the weight towards the passenger wheels in a left turn?

    Anyway, I have a post in the NC section of Miata.net where I’ve included a diagram of where it separated. I will post pics there soon.

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    • Gear Head
    • ★★★

    • Topics- 8
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    • Gear Head
    • ★★★

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    • Ace
    • ★★★★★

    I have never seen anything like that happen on a Miata…

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    • Gear Head
    • ★★★

    Well, today I discovered why the half shaft came apart. My differential mount is broken! One of the “ears” broke in two. That allowed enough play between the hub and the diff to allow the tripod to pop out of the socket. I’m not so bad off, since the mount is separate from the diff and joined to it by 4 nuts, I believe the NA/NB had an integral mount on the diff housing. I may have to drop the diff to do it. Trying to figure a way to get a new mount in there without taking too much apart… oy vey!!

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    • Pro
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    Yeah, wow. I can see how that broken ear would put a lot of force on the axle. Did it come out? Or was the cup sheared? A quick eBay search says that mount goes for $40-50. If you can do the work yourself, that’s not too bad. Look forward to hearing how it goes. As a club we have a lot to learn where the NCs are concerned. Careful, you may become the club’s NC suspension expert!

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    • Gear Head
    • ★★★

    The cup was certainly scarred up, but basically , the tripod had pulled out of the cup because the diff had more than it’s normal vertical movement.

    I looked for a used mount. There were lots of auto mounts but some of the MT mounts had cracked bushings (could be ungraded, but a PITA) and the others, I couldn’t tell. I ordered a new mount $$$Yeesh!!

    It has been a learning experience that I’m happy to share, and this has made it easier to replace my worn out suspension. So, many positive aspects to keep in mind. Looks like the power plant frame has reoriented the fasteners to make it easier to remove on the NC. I can hang if this is all I have to deal with in these times.

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    • Gear Head
    • ★★★

    Broken Diff Mount

    This isn’t my pic., but this is exactly what I have. Same driver side as well.

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    • Pro
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    So you’ve found others that this has happened to, interesting. I wonder if it has a built-in weak point like the NA/NB rear diff housings do to save the drivetrain in the event of a rear end collision.

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    • Gear Head
    • ★★★

    Interesting info, Dave. I didn’t know about the intentional weak spot. Seems like that would be the likely area for a break-away failsafe. Right now, I have both hubs removed awaiting the mount. Have yet to lower midpipe and PPF.

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    • Ace
    • ★★★★★

    man…that really sux…I have never seen that happen on a Miata that was not involved in an accident…the NA/NB diff housing is designed to break if that happens…

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    • Gear Head
    • ★★★

    Yea Joe, luckily the NC diff has a separate mount. The PPF is easier to remove too, as all the nuts face down. Since I’m not working, I’m taking my time doing this and replacing my suspension while I’m in there.

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