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Thread: Stripped out subframe bolt. Solutions..?

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    Default Stripped out subframe bolt. Solutions..?

    On my MS6 I’ve been chasing a small clunk sound on driver side. Happens on sudden braking and acceleration. Went and checked the subframe bolts on that side. One was not quite tight and the other, well upon tightening it just ended up pulling threads out. I can thread it back in, but cannot tighten it.
    My question is, what’s everyone’s opinion on best way to fix this. A few options, drill out and tap to m14, use timesert, use a helicoil, or lastly and most invasive, cut small hole and put a bit on backside of the bolt.
    I’m sort of leaning toward drilling out and tap to M14 personally. I’m a little concerned that timesert or helicoil may not work as well as I suspect.
    2005 Mazda 3 hatch

    2006 MS6

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    Default Re: Stripped out subframe bolt. Solutions..?

    Helicoil would be my first suggestion. Tapping larger (it might already be M14? it's pretty big) could just weaken things further. You might even get a closer size going to the next standard size, 1/2" should be close and you might be able to tap that. Ideally though you get access to the back side and weld in new metal/nut and then re-tap.

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    Default Re: Stripped out subframe bolt. Solutions..?

    Helicoils are great

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    Default Re: Stripped out subframe bolt. Solutions..?

    timecerts is the way to go... way stronger than helicoil
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    Default Re: Stripped out subframe bolt. Solutions..?

    Quote Originally Posted by TheMAN View Post
    timecerts is the way to go... way stronger than helicoil
    Yeah, they're better for sure, just more expensive and less readily available. Also, I'm not sure how much metal there is to work with on the backside of these...is it just a welded nut in the unibody? Or is there reinforced steel that's threaded?

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    Default Re: Stripped out subframe bolt. Solutions..?

    Timeserts are indeed pricey. Helicoil a little more readily available. I’ve never used a timesert before but have heard good things about them.
    The original size is M12x1.25. The bolt seems short too. It’s only 20mm long and only seems to actually grab anything near the end of it.
    I would like to fix it right but cutting into that main channel in the unibody to put in a nut scares me a bit. Also, I don’t have a welder. At least not now anyway.
    I did consider trying to just go imperial. I’ve got most tap sizes of course except the m12x1.25. I have 1.5, but I think threads are too effed for me to even bother trying to just ‘clean’ up threads.


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    Default Re: Stripped out subframe bolt. Solutions..?

    Quote Originally Posted by SomeGuy View Post
    I'm not sure how much metal there is to work with on the backside of these...is it just a welded nut in the unibody? Or is there reinforced steel that's threaded?
    Im not sure either. There isn’t a lot of information on the interweb regarding info on this.


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    Default Re: Stripped out subframe bolt. Solutions..?

    I'd definitely go helicoil. If you want to be even more sure about it, coat the exterior of the helicoil in JB Weld before threading it in; it's not going anywhere! I've also got a MIG and TIG setup if need-be!

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    Default Re: Stripped out subframe bolt. Solutions..?

    Quote Originally Posted by Como View Post
    Timeserts are indeed pricey. Helicoil a little more readily available. I’ve never used a timesert before but have heard good things about them.
    The original size is M12x1.25. The bolt seems short too. It’s only 20mm long and only seems to actually grab anything near the end of it.
    I would like to fix it right but cutting into that main channel in the unibody to put in a nut scares me a bit. Also, I don’t have a welder. At least not now anyway.
    I did consider trying to just go imperial. I’ve got most tap sizes of course except the m12x1.25. I have 1.5, but I think threads are too effed for me to even bother trying to just ‘clean’ up threads.


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    Which subframe bolt is it front or back one? They aren't usually that short from what I remember. It might have snapped off in there.

    I had to buy a special set to get taps in the right size for the subframe...most sets don't include ones big enough. Just checked and the smallest size in that set is M14. So the original isn't even M12. Also, you can't tap a different thread pitch in the same size, it will just tear out more metal.

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    Default Re: Stripped out subframe bolt. Solutions..?



    Yes back one. The bolt is definitely not broken as it’s tapered at end. The thread size and pitch are as posted. I double checked them. I went to chase the bolt thread but realized my m12 die was incorrect pitch as mine is 1.5, not 1.25 which is what bolt is.
    And ya I know I can’t just re tap to a different pitch. I just considered imperial as they’re a little more readily available. But still wasn’t able to find anything this weekend unless I was willing to travel (and pay) to go to spaenaur. I think I’m going to use a helicoil but look into getting a longer bolt. Grade 10.9 (metric) of course.


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    Default Re: Stripped out subframe bolt. Solutions..?

    Sucks there’s so little literature for ms6. I found a slightly better pic online. That’s the one. That bolts into unibody frame rail.



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    Default Re: Stripped out subframe bolt. Solutions..?

    Helicoil is holding in my rear shock lower bolt, which is welded nut.
    2 years strong now

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    Default Re: Stripped out subframe bolt. Solutions..?

    Right MS6...so it's possible (actually pretty likely) the subframe isn't the same as the MS3 and hence different bolt sizes/lengths/etc.

    TSC has higher grade metric and standard hardware in stock usually. Would be a good place to start. I'd find closest next largest size, drill/tap to it, call it a day. You'd have to drill/tap for a helicoil too and the benefit there is that it does preserve original thread size.

    I see you're in Guelph...I'm in KW and could lend my garage for the surgery at some point. I do have a lift, welder, taps/dies, etc...

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    Default Re: Stripped out subframe bolt. Solutions..?

    Hmmm @SomeGuy that’s a pretty attractive offer. I do have most of the tools here but having a lift and a second opinion are also definitely beneficial.
    I’m going to look into the hardware. I’ll need the correct size drill and a bolt. I have 2 M14 taps. 1.5 and 2.0. I’ll check tsc, boltsplus and fastenal this week and see what I can come up. My work will have that size I’m sure but they’ll be standard grade and likely socket head (Allen key).


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    Default Re: Stripped out subframe bolt. Solutions..?

    Quote Originally Posted by Como View Post
    On my MS6 I’ve been chasing a small clunk sound on driver side. Happens on sudden braking and acceleration. Went and checked the subframe bolts on that side. One was not quite tight and the other, well upon tightening it just ended up pulling threads out. I can thread it back in, but cannot tighten it.
    My question is, what’s everyone’s opinion on best way to fix this. A few options, drill out and tap to m14, use timesert, use a helicoil, or lastly and most invasive, cut small hole and put a bit on backside of the bolt.
    I’m sort of leaning toward drilling out and tap to M14 personally. I’m a little concerned that timesert or helicoil may not work as well as I suspect.
    You can try cutting a small hole in the where the nut is supposed to be welded on the inside but that's like last resort if nothing else works. Double check the control arm bushings and bolts as well because it's not common for the subframe to be moving. (There's 3 other bolts holding it down)

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