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Thread: Heli-coil for lower rear shock bolt '96 M3

  1. #1
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    Question Heli-coil for lower rear shock bolt '96 M3

    Stripped out...anyone have some long term experience with this fix? Car will be tracked (but not raced). It is a $60 fix versus $5-600. Don't want to cheap out (will be installing coil overs too), but not sure replacement needed. TIA

  2. #2
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    Never seen a helicoil used for lower rear shock on the spindle. The "safer" solution would be to swap out the trailing arm assembly that is integrated with the spindle. It's a nice surprise on the highway when the shock bolt comes out and you're riding on spring. Ask me how I know....

  3. #3
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    Drill it out and use a bolt and nut with washers. I don't have first hand experience, but I'd imagine a helicoil wouldn't hold up to abuse there.

  4. #4
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    Quote Originally Posted by LockDots View Post
    Drill it out and use a bolt and nut with washers. I don't have first hand experience, but I'd imagine a helicoil wouldn't hold up to abuse there.
    Yeah, I'd go this route, drill/tap for a larger bolt, or replace the hub assembly.

    While the rear shock isn't load bearing unless you're using coilovers, I wouldn't want to risk shock tower damage from the shock banging around if it were to come loose.
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  5. #5
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    Are you sure it’s stripped? The bolt can be a pain to get started. There is a slight angle. I assume you tried without the shock. Did you try a rethreader — might just be the first thread or two. Worst case, I agree with those who suggest drill through and bolt/washers/nut.

  6. #6
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    I’d be a lot more comfortable with a timesert than a helicoil in that location.

    But I would also try to tap it first.
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  7. #7
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    Helicoil is a PITA in that location. I used a Timesert on mine (after first botching a Helicoil installation). Timesert is more $$ but works very well. I've been running it on track for about 2 years now.

  8. #8
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    All are fine but I would not drill it to a larger tap size. These bolts fall out as they don't have much bolt stretch to begin with, going to a same length, bigger bolt is going to make it worse.

    I'd do the drill through and lock nut the back side - better bolt stretch, and good history of working great.
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  9. #9
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    Quote Originally Posted by Moron95M3 View Post
    All are fine but I would not drill it to a larger tap size. These bolts fall out as they don't have much bolt stretch to begin with, going to a same length, bigger bolt is going to make it worse.

    I'd do the drill through and lock nut the back side - better bolt stretch, and good history of working great.
    These bolts aren't backing out because of not enough stretch, they back out because by design when the trailing arm goes up, the shock goes up at an angle and there is a slight rotation taking place at that point of attachment. Repeat this tens of thousands of times, and you'll see issues. Thread lock and a clean washer is essential in this spot.

    I do not agree that drilling through would be the best solution.

    Tap it. If that won't work, then Time-sert. Worth the wait to do the job right.

    Also see:
    https://www.bimmerforums.com/forum/s...ear-shock-bolt
    Last edited by Hova; 12-09-2018 at 11:52 PM. Reason: Add link.
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  10. #10
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    The shock is not supporting that corner of the car, the spring in the upper control arm does that (unless you are true coil on shock in the rear). Any form of thread repair will work just fine. Heli-coil kits are available at your local Oreilly's for around $24. Time-sert you have to order and to me, drilling a hole through it isn't the proper way to fix it.

  11. #11
    NeilM is offline Member BMW E36 M3 Expert
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    Drilling a through-hole isn't great because the back side doesn't provide a flat surface for a nut/washer to seat. You could take a grinder to it, but then you're also weakening the part.

    I stripped one of mine several years ago and Helicoiled both sides. You do need to be a bit careful when drilling out the hole to keep it properly aligned. It's also helpful to use a cobalt drill bit, since the arm's base material is hard and you're enlarging to a big-ish diameter hole (~14mm).

    Replacing the whole trailing arm would be absurd. Mine is a track car and this fix has been holding like a champ. I'd suggest verifying the bolt torque after a few hundred miles, and after that don't worry about it.

    Neil

  12. #12
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    Quote Originally Posted by NoLastName View Post
    Helicoil is a PITA in that location. I used a Timesert on mine (after first botching a Helicoil installation). Timesert is more $$ but works very well. I've been running it on track for about 2 years now.
    After using Timeserts I'll never go back to Helicoils.

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