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So what's the final verdict? I have a 2006 Exige. I'm going to have these bolts checked out by my shop when I swap coilovers, but is it worth it to just replace with 12.9 bolts while they're in there?

Yes, and you should replace them every time you remove them IMO since they cost like $12 total
 

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https://www.fastenal.com/products/details/1139623?term=m10+50&r=~%7Ccategoryl1:%22600000%20Fasteners%22%7C~%20~%7Ccategoryl2:%22600039%20Sockets%22%7C~%20~%7Ccategoryl3:%22600040%20Socket%20Cap%20Screws%22%7C~%20~%7Csattr06:%5E%22Class%2012.9%22$%7C~

25 at 50 cents each. Your local dealer can order them and you can save on shiping.
 

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I wanted to add this to my previous post (post#51) but I guess it is too old for LotusTalk to allow me to edit it. This is the video of the bolts breaking on my car. (@09:25)
https://youtu.be/ZCIUPasq2EQ?t=9m25s
 

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I’ve spoken to someone that works on tracked Eliges and they’re hesitant to do 12.9 because they can be more brittle.

Anyone have a source for 10.9 bolts that will work?
 

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I’ve spoken to someone that works on tracked Eliges and they’re hesitant to do 12.9 because they can be more brittle.

Anyone have a source for 10.9 bolts that will work?
https://www.engineersedge.com/hardware/loading_capacities_bs449_bolt_grade_109__14821.htm
https://www.engineersedge.com/hardware/loading_capacities_bs449_bolt_grade_129__14822.htm

https://itstillruns.com/129-bolt-shear-capacity-11415080.html


From what I read it seems shear strength is derived from its measured tensile strength. But if you have proof that 10.9 has a greater ability to resist shearing than a 12.9 grade bolt please post it up to educate us. I am not arguing - I, just like everyone else wants what is best for our cars! Thx
 

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https://www.engineersedge.com/hardware/loading_capacities_bs449_bolt_grade_109__14821.htm
https://www.engineersedge.com/hardware/loading_capacities_bs449_bolt_grade_129__14822.htm

https://itstillruns.com/129-bolt-shear-capacity-11415080.html


From what I read it seems shear strength is derived from its measured tensile strength. But if you have proof that 10.9 has a greater ability to resist shearing than a 12.9 grade bolt please post it up to educate us. I am not arguing - I, just like everyone else wants what is best for our cars! Thx


I really don’t know. That’s why I asked!

For my own edification, which part number in the attached is the bolt in question?

Any other vulnerable bolts or that’s it?
 

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It’s not a bolt, it’s #32 and nut #29. 32 is a ball joint at one end of the rear toe rod.
 

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I've read through this thread several times through the years and one thing I don't really see talked about is the quality of the original bolts that have been subject to failures. Lotus is not known for having the highest quality standards, and like most companies, I'm sure they rely on the lowest bidder when sourcing parts for manufacture. My background in aviation has kept me aware of hydrogen embrittlement in hardware during its service life, leading to sudden unexpected failure. To those that have been asking; yes 10.9 and 12.9 bolts have higher strength than 8.8 bolts but they are more susceptible to embrittlement than lower grade bolts. When reading about how and when some of these failures occurred I just wonder if the bolts are failing due to embrittlement caused by "less than optimal manufacturing" and environmental exposure. Here is a link to a good two-page read on bolt failure due to embrittlement.
http://www.boltscience.com/pages/the-stronger-the-better-is-not-necessarily-the-case-for-fasteners.pdf
 

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I hate to keep bringing an old post back from the dead but I thought I'd show everyone what I found tonight. After seeing this thread pop up again a few weeks ago it spurred me into ordering some new bolts for the steering arm to hub (front) & carrier to hub carrier (rear) (Service parts manual figure 31.01, item 5 & 6 [front], and figure 31.03, item 05 [rear]). I ordered good quality 12.9 hardness bolts from a reputable supplier (McMaster-Carr) and got them installed tonight. Looking at the bolts I removed from my 2005 Elise I found corrosion beginning to form on the center section of the bolt which makes me wonder if the failures people have with these bolts might be due to corrosion and embrittlement (see the post above).

I had assumed that the bolts on my car would be fine due to the low mileage (10,033), but after seeing the beginnings of the corrosion I'm glad I elected to change the bolts now before they had a chance to fail. The bolts are inexpensive and the replacement is easy, repairing the damage if they break while driving is hard.
 

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I don't know whether what you show is a cosmetic issue or a structural one, but I wonder to what extent the mating surfaces (that you did not replace) could also be subject to a similar process.
 

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I don't know whether what you show is a cosmetic issue or a structural one, but I wonder to what extent the mating surfaces (that you did not replace) could also be subject to a similar process.
These bolts are known to fail at less than their design yield strength, no one that I know of has done objective testing to determine the root cause. I know from my years in aviation maintenance that corrosion is typically the root cause when failures occur below design thresholds. IMHO, corrosion is corrosion, 'cosmetic' corrosion is structural corrosion that is just in its early stages. Whether the bolt failures are caused by Intergranular Corrosion, Stress-corrosion cracking, or Hydrogen embrittlement the results are the same. I have a sneaking suspicion that the failures are caused by hydrogen embrittlement, the most common cause is short cuts in manufacturing (typically the elimination or delay of the baking cycle after plating). Manufacturers such as Lotus typically source parts from the lowest cost vendors they can find and I've yet to find anyone that thinks Lotus used high-quality fasteners on their cars.
 

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@Jetblast thanks for your explanation. Should we stick to stainless or titanium? What do you recommend? I will soon change all the suspension bolts in my car and I want to make sure I use the best quality.
 

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@Jetblast thanks for your explanation. Should we stick to stainless or titanium? What do you recommend? I will soon change all the suspension bolts in my car and I want to make sure I use the best quality.
Not Jetblast, but...

Neither one, both are too weak. In general for suspension components you want Class 10.9 bolts from a reputable supplier. I use McMaster-Carr.

Also, use loctite (usually blue) and proper torque as per the Lotus service manual, and paint mark the nuts and bolts for easy visual inspection.

HTH, -Ed
 

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Not Jetblast, but...

Neither one, both are too weak. In general for suspension components you want Class 10.9 bolts from a reputable supplier. I use McMaster-Carr.

Also, use loctite (usually blue) and proper torque as per the Lotus service manual, and paint mark the nuts and bolts for easy visual inspection.

HTH, -Ed
12.9 Bolts are stronger yet.
 
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