Rear Stabilizer Bar bushing question - North American Motoring


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Rear Stabilizer Bar bushing question

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Old 03-25-2017, 02:16 PM
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JPKjr JPKjr is offline
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Rear Stabilizer Bar bushing question

I am getting ready to replace the stabilizer bar bushings in my 2010 Cooper. It has the 16-17mm diameter stabilizer bar.

I want to change the bushing U-bracket hold down bolts to stainless steel when I do that. Anyone here know the size of the stock bolts used to fasten down these brackets?

Thanks for any help.
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Old 04-14-2017, 05:08 PM
seandallen seandallen is offline
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The original bolt is specified as "M8X12-8.8-ZNS3". Translated M8 (8mm head) x 12 (12mm long - it's a short bolt) - 8.8 (the class of the material. In this case, medium carbon steel, quenched and tempered) - ZNS3 (indicates a protective coating. In this case, a zinc/lubricated silicate inorganic type). There is no specified thread pitch, but BMW generally uses 1.25mm unless the bolt is inside the engine. This bolt has many applications across the BMW/MINI spectrum. You could easily keep a dozen on hand (you can buy them for about US$1.50), and find them handy.

That said, it's good that you mention that you thinking of replacing them with stainless steel, which I'd recommend against. The stock bolt has a minimum yield strength (the maximum load at which a material exhibits a specific permanent deformation) of 640 MPa (1MPa = 1N/square mm = 145 pounds/square inch), while stainless steel can yield at 210 MPa - 450 typical). It also has a minimum tensile strength (the maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing) of 800 MPa, while stainless can yield at 500 MPa - 700 typical. As you can see, a stainless steel bolt just isn't as strong as a carbon steel bolt. I would think you wouldn't want to sacrifice that strength in your sway bar hold downs.

You might be able to find a M8x12-10.9 or M8x12-12.9 which are a stronger alloy steel bolt. They are stronger (especially the 12.9 grade), but at the expense of being a little more brittle. The carbon steel might be able to stand little more torquing through various driving scenarios.

If you're just looking for a shiny bolt, you might try polishing the stock bolt with a Dremel tool, then coating the head with some polyurethane after you've installed it. Then you will retain the characteristics of the original bolt as engineered.

Hope this is helpful.
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Old 05-09-2017, 04:17 PM
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Quote:
Originally Posted by seandallen View Post
The original bolt is specified as "M8X12-8.8-ZNS3". Translated M8 (8mm head) x 12 (12mm long - it's a short bolt) - 8.8 (the class of the material. In this case, medium carbon steel, quenched and tempered) - ZNS3 (indicates a protective coating. In this case, a zinc/lubricated silicate inorganic type). There is no specified thread pitch, but BMW generally uses 1.25mm unless the bolt is inside the engine. This bolt has many applications across the BMW/MINI spectrum. You could easily keep a dozen on hand (you can buy them for about US$1.50), and find them handy.

That said, it's good that you mention that you thinking of replacing them with stainless steel, which I'd recommend against. The stock bolt has a minimum yield strength (the maximum load at which a material exhibits a specific permanent deformation) of 640 MPa (1MPa = 1N/square mm = 145 pounds/square inch), while stainless steel can yield at 210 MPa - 450 typical). It also has a minimum tensile strength (the maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing) of 800 MPa, while stainless can yield at 500 MPa - 700 typical. As you can see, a stainless steel bolt just isn't as strong as a carbon steel bolt. I would think you wouldn't want to sacrifice that strength in your sway bar hold downs.

You might be able to find a M8x12-10.9 or M8x12-12.9 which are a stronger alloy steel bolt. They are stronger (especially the 12.9 grade), but at the expense of being a little more brittle. The carbon steel might be able to stand little more torquing through various driving scenarios.

If you're just looking for a shiny bolt, you might try polishing the stock bolt with a Dremel tool, then coating the head with some polyurethane after you've installed it. Then you will retain the characteristics of the original bolt as engineered.

Hope this is helpful.
Nice answer!
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