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      04-12-2017, 10:48 AM   #1
///ASN
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Suspension bolts

What is the general consensus for the bolts on suspension?
Some saying they can be reused, some say not.
With the control arm bolts, they are torqued to 165Nm + 90 degree, think they are torque to yield bolt and should be replaced?
What about the bolts holding the end links etc?
Many thanks.
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      04-12-2017, 09:54 PM   #2
bradsm87
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I have always re-used them on all of my cars, sometimes several times. No issues.
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      04-13-2017, 12:50 AM   #3
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As I understand it: You're supposed to replace any torque to yield bolt.

Even with that said I've always reused the bolts in my cars over the years and I imagine many workshops do the same.

I'm personally not planning on continuing this trend as hey...they can't be that expensive to replace...Can they?
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      04-13-2017, 12:54 AM   #4
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It gets very expesnive to replace every bolt thats TTY in the suspension. If its not damaged and the bolt still threads in smoothly i usually just reuse it.

I would NOT recommend putting angle on the bolt again. I would look up a chart for a sensible torque value based on the size of the thread and location used.
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      04-13-2017, 03:49 AM   #5
///ASN
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Quote:
Originally Posted by vtl View Post
It gets very expesnive to replace every bolt thats TTY in the suspension. If its not damaged and the bolt still threads in smoothly i usually just reuse it.

I would NOT recommend putting angle on the bolt again. I would look up a chart for a sensible torque value based on the size of the thread and location used.
Attached a torque value file from a member here

1st line below is what I can get from the internet as well as ECS tunning DIY
2nd line below is what the PDF says on page 7 about M12 thread bolt

Front control arm to sub frame = 68Nm + 90 degree
PDF saying this Hex bolt with washer 31106763928 (M12X1.5X115-8.8) = 87Nm?

Rear lower control arm to knuckle/sub frame = 165Nm
PDF saying this Eccentric Bolt 33306784983 (M14X1,5X95-10.9 bolt) = 200Nm?

Also, all those bolt threads M8 M10 M12 M14 that Titium shows in the below thread doesn't have a 8.8 or 10.9 or 12.9 value, may I ask how to interpret the table there?
http://www.e90post.com/forums/showthread.php?t=1362166
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File Type: pdf BMW Torque Values.pdf (172.4 KB, 34 views)
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      04-13-2017, 04:03 AM   #6
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I normally do M10 to 75Nm, M12 to 100, M14 to 165Nm

If you look at an engineering chart for torques those will be about right for high tensile bolts. Most bmw stuff is 10.9 in the suspension . You have to use common sense though, sometimes huge threads are used for drain plugs etc so I would only apply these for stuff like suspension and drivetrain bolts.
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      04-13-2017, 08:20 AM   #7
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REPLACE

Once one wiggles itself loose you'll wish you did. Ask me how I know

I'm talking about the labeled one time use bolts

They're labeled that for a reason
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      04-13-2017, 10:32 AM   #8
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Hi ///ASN - a very interesting question, thank you.

Torque To Yield (TTY) is the (yield) point at which a material has moved from the elastic limit to the plastic zone and permanent deformation will occur according to Young's Modulus of Elasticity.

Once a material has exceeded the proportional limit then the material can no longer return to the elastic modulus.

A TTY would never be applied to a fastener where a gasket would be in place as the fastener cannot expand or contract according to the operating conditions.

In a suspension component, requiring angular force, the torque applied to the fastener takes it to the proportional limit and any further angular force required takes the material into the plastic zone. The 'stretched' fastener is permanently deformed and is NOT recommended to be used again.

BMW AG provides Normative reference GS 90003-2 which details tightening torque for metric thread and calculating procedures. This is the standard to be observed if no cross references are provided for tightening torque in the repair instructions.

Predominately BMW uses thirteen different surface treatment coatings.
(ZN) Yellow and (ZNS) Silver can easily be identified visually. The metric class is marked on the fastener cap eg.4.6, 4.8, 5.8, 8.8, 9.8, 10.9 and 12.9 Thirdly the thread pitch is identified as fine or coarse.

Now that you have identified the fastener then it can be cross referenced to GS 9003-2 and the correct torque settings can be applied without guestimating.

Attached is tightening torque extracted from BMW GS 90003-2.
Confucius said - I hear and I forget. I see and I remember. I do and I understand.
///ASN I hope this is beneficial.
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File Type: pdf BMW GS 90003-2 Tightening Torque.pdf (972.1 KB, 172 views)
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