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This issue just happened to me as well, albeit self inflected from over torqueing a garbage KYB nut that came with a replacement shock mount. Mine was rear driver's side, right hand stud, with about an inch left from the top of the stud to the sheared off end.

I chose the drill out route using a regular 18 volt hand drill and cobalt bits. My car is the sedan, so I had to use a 90 degree adapter for the drill thanks to limited trunk space. I also drilled from the under the car once a pilot hole was through the stud from the top. I drilled a 5/16 hole and used a 44mm long M8 x 1.25 grade 10.9 bolt as a replacement. I used two washers, including a 1 inch wide one, under the head of the bolt to spread force across the drilled out head of the stud in the event the drill through left it structurally compromised. So far I have elected not to glue / weld the bolt in place for easier removal in the event this fix doesn't work permanently. The reattached mount looks properly aligned and nice and flush with the top of the wheel mount.

So far no problems from test driving. Has anyone else who has performed this fix experienced any problems since? Also thanks to those who posted their experiences with this. I don't think I would have attempted a fix without the advice here.
 

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Had this happen on a old Volvo 850 my daughter drove, very common. I would just grind off top that is tack welded and use a grade 8 bolt. I would not recommend a cheapo home depot bolt, get a real bolt, plated would be nice. Either way anti seize goop is your friend here.
 

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sorry for reviving this thread.. I sheared off the driver side rear strut bolt when I over tighten the bolt. It is the left side of the 2 bolt ( the one closer to front )

Thanks for this thread and this video about removing panel, it made this a much faster job than I anticipated.

I first use a center punch, then use 1/8" drill bit to start, and finally drilled out the old bolt with 5/16" bit, the hole is just right for the m8 to go through.

Then I sand off the paint on the old bolt surface, applied the grey jb weld and put the bolt in, with a wrentch on top to keep the bolt from rotating, I fastened the strut mount back in to keep the bolt in place, then applied a bunch more jb weld around it to keep from rotating in future.

Total time spend is about 2-3 hr, including cleaning the under seat area.

Many thanks for the instruction!

Car Hood Vehicle Steering part Motor vehicle


Motor vehicle Automotive tire Machine Auto part Steering wheel
 

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Happy to know I wasn't the only one that ran into this problem. I have a '07 Mazda 3 Sedan, and broke the driver side rear bolt from over tightening. Lucky for me I found this great thread and it helped me tons. For the rear bolt there was enough room for me to get my 4.5" hand grinder in and cut the head of the bolt. After which, all I did was tap the rest of the bolt down and inserted a new M8 screw and washer. Like a few others here I chose not to weld the new bolt on in case I run into trouble in the future. So far looks and feels great, only took about 2 hours to do everything. Thanks all for sharing your experience.
 

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i got lucky with my son's car... he had been driving it for months with that clunking at the rear trunk area...
Gas Circle Auto part Metal Fashion accessory


you can see the obvious weak points of these aluminum casted mounts...
Door Gas Circle Metal Fixture


my local autozone carries BOTH KYB (OEM aluminum) and DORMAN (steel upgrades for $20 each more.Boo)

I went with the cheaper option since they will cover the Limited Lifetime Warranty on either choice.

Material property Packaging and labeling Font Gadget Box


of course, i've use anti seize compound on all the exposed threads to make it easy to remove if they ever break again.
 

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Blind Rivet nuts are much easier to repair these shock areas. Just saying. I see a lot of labor that some have done that was perhaps not really necessary. It what I personally have always used with great success. The rivets are inexpensive, but you do need to buy the installation pliers.

I would also advise to paint the aluminum top shock bracket and maybe after the new shock mount installed to seal the complete area with paint of undercoating to prevent the corrosion in the future?
 

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i say if you don't want to re-do the procedure again, go with the more expensive dorman steel mounts... i posted my pictures of the cast aluminum housings and can see why they'll break apart.

of course, i coated the exposed bolt threads and nuts in anti-seize compound since that's what i got on hand at the time & it's doing OK.

i also coated the lower shock bolt and threads before re-assembly to avoid any rust-jacking in that area for future easy removal once the rear shocks break down/leak

at least it took about a decade or so for these to fail ( but this car was mainly on highways and smooth blacktop roads)
 
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