New springs, broken bolt and opinion on 10.9 vs bolts12.9

[Trevor /chedder]

Started to replace my springs today. The prosport ones looked terrible and definitely sagged over the three years they've been fitted.
Broke a bolt on the front shock, one of the pair at the bottom.
Failed to get it out so awaiting a new bolt removal tools and better drill bits.
I've ordered a new bolt, the BMW one is a 10.9 hardness, Amazon had some 12.9 in the right size and much cheaper. Do you think that will be ok?

 

[ExMX5owner]

Yeah not a problem given its application. . a 12.9 is going to damage the part its bolted to in the event of a catastrophic failure. but then so is a 10.9 in this instance..The amount of springyness "for the want of a better term" is not really a factor nor is it significant in this application, Torque settings should not be an issue, But drilling it out if you ever have to, would be a bigger headache than a 10.9 already is...

The numbers are actually the tensile strength , 8.8 10.9 12.9 and so on, lower numbers or no numbers can stretch and bend a bit, higher number do not , but are more likely to snap under hideous loads or shock, for example I wouldn't worry too much if I had to fit 8.8s where the 10.9s are.... Corrosion resistance is also a bit of a factor, higher tensile are more resistant to corrosion. there is a lot more science to it, much I have forgotten being retired from engineering for so long. but the bullet points are here...When I was in the trade there was no such thing as a 12.9 and I might suggest that when your 3 was built there wasn't either. Such are the advances in metallurgy, and production.

 

[Trevor /chedder]

Yeah not a problem given its application. . a 12.9 is going to damage the part its bolted to in the event of a catastrophic failure. but then so is a 10.9 in this instance..The amount of springyness "for the want of a better term" is not really a factor nor is it significant in this application, Torque settings should not be an issue, But drilling it out if you ever have to, would be a bigger headache than a 10.9 already is...

The numbers are actually the tensile strength , 8.8 10.9 12.9 and so on, lower numbers or no numbers can stretch and bend a bit, higher number do not , but are more likely to snap under hideous loads or shock, for example I wouldn't worry too much if I had to fit 8.8s where the 10.9s are.... Corrosion resistance is also a bit of a factor, higher tensile are more resistant to corrosion. there is a lot more science to it, much I have forgotten being retired from engineering for so long. but the bullet points are here...When I was in the trade there was no such thing as a 12.9 and I might suggest that when your 3 was built there wasn't either. Such are the advances in metallurgy, and production.

Thanks so much, for such a detailed answer, great to be reassured by a pro. Just got to get the snapped one out now

 

[Synclare]

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[B21]

What pitch is the bmw bolt..they tend to use finer threads which provide greater torque capability…the 12.9 vs 10.9 only applies if it’s the same thread pitch..

 

[Trevor /chedder]

The BMW one is M12 1.75 20mm. So I've made sure the thread is 1.75. Thanks for the input, it's always a bit scary wandering off the exact BMW part!

 

[Trevor /chedder]

This arrived today. So I'll be at it tonight!

 

[Scooblitz]

Have you checked prices for BMW bolts rather than going off-piste in the after market?

Generally, not unreasonable and it pays in the long run to show your face in your local BMW parts department. Got to know my parts guy and usually get 10-15% discount. Not much when talking about nuts bolts etc but when doing a cooling system overhaul, sills and other bits, it can add up.

Stevie

 

[Trevor /chedder]

Might pop in after work. Got my MOT tomorrow so was short of time.

 

[bombur]

Have you checked prices for BMW bolts rather than going off-piste in the after market?

Generally, not unreasonable and it pays in the long run to show your face in your local BMW parts department. Got to know my parts guy and usually get 10-15% discount. Not much when talking about nuts bolts etc but when doing a cooling system overhaul, sills and other bits, it can add up.

Stevie

BMW group 1 Lincold (old Sopers), as well as giving a discount also offer free delivery. Not sure if a min spend though