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  #21  
Old 03-11-2015, 05:13 PM
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Quote:
Originally Posted by David.X5 View Post
I have a PhD in engineering and I don't get why these bolts are spec'd like this. I am convinced you would tear that thin aluminum panel long before you would break one of those bolts.
I'm sure you're aware that stress is applied horizontally onto plate, therefore they didn't have to make it thick. I'm with you on the bolts, why not have regular 10.9 grade that can be torqued numerous times without issues.
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  #22  
Old 09-07-2015, 04:10 PM
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Coming back to this. Anyone who found alternatives discover anything to report?

Are those Dodge bolts good to use? Do they fit the stock nuts?
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  #23  
Old 09-07-2015, 04:29 PM
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While I appreciate the fast response. I am not comfortable re-using the old bolts.
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  #24  
Old 09-07-2015, 06:20 PM
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Quote:
Originally Posted by cncmastr View Post
While I appreciate the fast response. I am not comfortable re-using the old bolts.
Then, out of curiosity, why are you looking for alternatives to the factory bolts? I realize they are $75, but if you are worried about something, those bolts were designed for the purpose.

To me, any decent replacement grade bolt would do the job. I'm guessing these are stretch bolts/TTY so that they will shear in the case of an accident... so you may compromise that a little, but if you hit something hard enough for that to be an issue... other things might be more concerning.

Personally, I plan on re-using the stock bolts...
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  #25  
Old 09-07-2015, 08:52 PM
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recently had engine replaced, then the transmission went out about 1k miles later.

replaced tranny, and car was great.... Then a squeak developed. slight at first, then horrible. I thought it was the front differential, so I changed the fluid. Helped some, but still there.

Then I realized I had read somewhere someone saying they had a horrible squeak if they reused the old reinf. plate bolts.

so, bought some new ones, reinstalled to spec and...voila. No more squeek.
The old bolts were clearly no longer straight.

so I think after 3 removal/reinstalls, they are done. Check the bolts carefully: if you see that they are no longer true, I recommend replacing them.

so yes, despited all the engineers in the thread, the bolts do make a difference
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  #26  
Old 09-07-2015, 10:49 PM
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Quote:
Originally Posted by cham View Post
recently had engine replaced, then the transmission went out about 1k miles later.

replaced tranny, and car was great.... Then a squeak developed. slight at first, then horrible. I thought it was the front differential, so I changed the fluid. Helped some, but still there.

Then I realized I had read somewhere someone saying they had a horrible squeak if they reused the old reinf. plate bolts.

so, bought some new ones, reinstalled to spec and...voila. No more squeek.
The old bolts were clearly no longer straight.

so I think after 3 removal/reinstalls, they are done. Check the bolts carefully: if you see that they are no longer true, I recommend replacing them.

so yes, despited all the engineers in the thread, the bolts do make a difference
I completely believe you that after 3 uses you can run into issues. And thank you for posting the squeak can be caused by reusing the bolts. Others who have reused them once have reported being okay... so as you say, inspect the bolts and reuse knowing if they make noise you will have to replace.
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  #27  
Old 09-08-2015, 05:53 PM
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Quote:
Originally Posted by trader4 View Post
This is one of the more outrageous examples of screwing
customers.
Sure is, reminiscent of the $90 wiper blades owners used to have to buy directly from BMW for the e39. BMW got in trouble for that if memory serves...
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  #28  
Old 04-14-2016, 03:39 AM
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Quote:
Originally Posted by bmw540san View Post
My only concern with reusing them is that they're probably "tired" and more likely to snap, not necessarily during reinstalling but later on during driving. But, you just might be right about not worrying about them.

Just to play it safe I'll probably go with 10.9 grade M10X60 from Ace Hardware of all places. It's about $25 for 6 flanged bolts and 6 flanged nuts. I've checked online and some local places and $25 is about cheapest for 10.9 grade.

Obviously, I'll check first that 5mm extra is non to long but I'm almost certain that it's not.
Would these be torqued down the same way as the OEM ones or maybe just stop at 41 and ignore the added 90 degree turn?

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  #29  
Old 04-14-2016, 09:40 AM
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This looks like an old thread, but I would imagine you would want to tighten them to the same spec (i.e., with 90deg turn). I just reused my original bolts after changing the front diff fluid, didn't add the full 90deg turn, and am definitely hearing some creaking underneath at slow speeds. I'm going to go back and re-tighten but would consider replacing if I could find a cheaper alternative to OEM like these.
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  #30  
Old 04-14-2016, 04:47 PM
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Quote:
Originally Posted by David.X5 View Post
The prices have gone nuts. They used to be $3-4 each, which was still pricey, but not worth the trouble of finding an alternative.

Those bolts are M10 x 55mm long. Grade 10.9. I think there is space for a slightly longer bolt - 60mm should be fine.

On McMaster-Carr, a M10 x 60mm flange-head cap screw in grade 10.9, Zinc plated to JIS standards, is $7.58 for 10. (part number 95735A661). This is 1.25 mm thread pitch, so you would have to pick a matching nut with the same thread pitch.
Careful with changing thread pitch on these, or any bolts where torque is important.

The standard pitch for M10 is 1.5mm. If you change that to 1.25mm, the torque value and angle value will be different. The angle is easy to consider - 90 degrees on a 1.5mm pitch bolt will stretch the bolt by 0.25 * 1.5 = 0.375mm. On the 1.25mm pitch bolt, it will be 0.25 * 1.25 = 0.3125mm. The initial torque value will be different, but not so easy to analyze because that is dominated by friction.

There is nothing magic about these class 10.9 bolts BMW overcharges you for. During the torquing of the 90 degree angle, the bolt (and maybe nut) exceeds the yield stress and deforms plastically. This work hardens it, making it stronger (higher yield strength; not affecting the tensile strength), but not stiffer than when it was new. This "feature" is usually why TTY is used - you get the increased strength you want, but without increasing stiffness (e.g., when a certain amount of compliance is required).

So when you remove and reinstall them (like I do), you should NOT torque them and then apply the same angle as you would use on new bolts. If you do that, each time you R+R them you will be pushing further into the plastic region, eventually exceeding the tensile strength, at which point they will break, either while tightening them or when you're out driving.

Ideally, you would torque them back to their exact stretch before you removed them, but you do not want any further plastic deformation.

A completely different way to analyze this issue, not relying on engineering, would be to phone a few BMW dealers and ask how long it will take to get these parts in stock. My understanding is they don't stock them because they don't use them. They re-use the existing ones, thinking far less about it than I or others on this list have. I expect they'll do this until it causes a problem - and are still waiting for that to happen. It would be good to know what torque+angle procedure they follow on re-used bolts, but it should be different from that used for new bolts. Hopefully they know that.
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Last edited by oldskewel; 04-14-2016 at 11:25 PM.
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