foskid
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| posted on 23/5/11 at 04:32 PM |
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bolt strength
Hi folks,
At the moment my suspension is assembled using 8.8 grade bolts during the build, are these sufficient or do I need to upgrade them for final assembly
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Cheers, John.
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omega0684
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| posted on 23/5/11 at 04:38 PM |
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8.8 will do nicely! 
I love Pinto's, even if i did get mine from P&O!
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Neville Jones
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| posted on 23/5/11 at 04:55 PM |
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If they're the size most use, 4.6's will be more than enough!
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iank
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| posted on 23/5/11 at 05:22 PM |
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It's been argued that for suspension 8.8 are a better choice than 12.9 due to harder bolts failing by snapping rather than bending when hitting
a curb hard.
Same reason crane hooks aren't made of high tensile steel (or so I was told at school) since if overloaded you want them to bend slowly rather
than snap.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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mcerd1
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| posted on 23/5/11 at 05:57 PM |
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quote:
Originally posted by iank
It's been argued that for suspension 8.8 are a better choice than 12.9 due to harder bolts failing by snapping rather than bending when hitting
a curb hard.
sounds about right to me, but I can't see it making that much difference in real life
there are all kinds of odd grades out there (4.6, 8.8, 10.9 and 12.9 being the most common)
the first number is related to th tensile strength (higher the better)
the secnond is how tough it is (lower numbers will bend more before breaking)
I can dig out the stuff to tell you how strong / tough they are if anyones really bothered...
[Edited on 23/5/2011 by mcerd1]
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snapper
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| posted on 23/5/11 at 06:12 PM |
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Most suspension bolts on production cars are 10.9
Certainly the Sierra diff bolts are 10.9
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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mcerd1
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| posted on 23/5/11 at 06:20 PM |
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quote:
Originally posted by snapper
Most suspension bolts on production cars are 10.9
Certainly the Sierra diff bolts are 10.9
but ford use 10.9 for almost everything, and the sierra is twice the weight 
[edit]I know its not really as simple as that....
[Edited on 23/5/2011 by mcerd1]
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flak monkey
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| posted on 23/5/11 at 06:26 PM |
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I worked this all out ages ago.
An 8.8 grade bolt has a shear strength of about 375N/mm^2. Which works out to be 3.15 tonnes for an M12 8.8 bolt in single shear
All suspension bolts in a seven are in double shear... so 6.3tonnes more or less.
Thats a lot more than you could hang from the suspension brackets.
Mild steel rods would be strong enough at that diameter
Infact you would be better if designing from scratch to use M10 bolts rather than M12...but who am I to argue with convention?
Sera
http://www.motosera.com
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mcerd1
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| posted on 23/5/11 at 06:34 PM |
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^^ but if you use too small a diamiter of bolt you may end up with a bearing failure rather than sear, especial on a thin suspenssion bracket
[Edited on 23/5/2011 by mcerd1]
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flak monkey
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| posted on 23/5/11 at 06:49 PM |
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I worked that out too. Even M8 is plenty big enough for any forces one single bolt could forsee... Bearing in mind that you have 4 times that strength
at the front and a bit more than 4x at the rear...
Sera
http://www.motosera.com
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mad4x4
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| posted on 23/5/11 at 07:12 PM |
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quote:
Originally posted by Neville Jones
If they're the size most use, 4.6's will be more than enough!
Errr no they won't - neither will A2 or A4 Stainless, Suspension can take a lot of loading. Yes I know that this is in the horizontal plane
compared to a tensile pull on a bolt but I'd always had a strong bolt over a piece of cheese. I would expect Mr. IVA would also say no if you
used unstamped or 4.6 grade bolts. For the sake of a few pence use 8.8's
>>>"Grabs FLAC Jacket and Runs for Cover..>>>"
Scot's do it better in Kilts.
MK INDY's Don't Self Centre Regardless of MK Setting !
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flak monkey
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| posted on 23/5/11 at 07:22 PM |
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The reason not to use stainless is different. A4-70 is technically the same as 8.8 to make no difference...
4.6 bolts ARE more than strong enough, but would fail IVA... but there we go...
Like I said before the brackets will give out way before the bolts will...
Sera
http://www.motosera.com
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Liam
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| posted on 23/5/11 at 09:57 PM |
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quote:
Originally posted by mcerd1
^^ but if you use too small a diamiter of bolt you may end up with a bearing failure rather than sear, especial on a thin suspenssion bracket
[Edited on 23/5/2011 by mcerd1]
You shouldn't - because the bolt should not be used as a bearing!
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mcerd1
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| posted on 23/5/11 at 10:11 PM |
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quote:
Originally posted by Liam
quote:
Originally posted by mcerd1
^^ but if you use too small a diamiter of bolt you may end up with a bearing failure rather than sear, especial on a thin suspenssion bracket
[Edited on 23/5/2011 by mcerd1]
You shouldn't - because the bolt should not be used as a bearing!
I mean crushing or ovaling of the bolt or the part that the bolt goes through
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foskid
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| posted on 24/5/11 at 07:49 AM |
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OK, thanks for the advice gents, I guess I'll stick to 8.8 bolts
Cheers, John.
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Doctor Derek Doctors
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| posted on 24/5/11 at 12:25 PM |
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To be honest how the bolts are used is far more critical than the material they are made of. If the positioning and mating is well designed then
8.8's are no problem.
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