Which bolt grade?

[PotvinGuy]

I just redid my steering with nice stainless hardware, and a machinist rod guy was horrified. He said I should use grade 8 stuff, but couldn't explain why. About all I've found online is grade 8 maybe has more tensile strength than SS. Well, I guess that is nice, but is it necessary for this application?

 

[2old2fast]

I used stainless on all the front hardware on mine ,40K miles w/ no wear I can see...mech. engineer told me bolts are only rated in tensile strength, not shear strength, said on my application , either grade 5 or stainless was up to the task..
dave

 

[choppinczech]

The tensile strength is close. The yield is less.

Still not an issue though. IMHO

 

[Indycars]

What does is say on the head of your bolts? Most SS bolts are considered to be Grade 2 compared to steel.

Be sure to use anti-seize when threading SS into aluminum.

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&ved=0CEoQFjAK&url=http://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf&ei=5xIvVY_BL4PusAXq8YHIDg&usg=AFQjCNG4UhC2wSjIK7FrQFFw0f1xPOJe5g&sig2=w8mqNXGlikYMxZwOdJxgPQ&bvm=bv.91071109,d.b2w

 

[PotvinGuy]

And I find that not all SS is the same. "Ordinary" SS is called 304 or 18-8. But ARP apparently makes SS hardware that is as good or better than grade 8 steel. My head hurts...

 

[benT]

I used high strength SS on my entire front end. Some sourced from ARP, the rest from Totally Stainless which has the larger sizes like 1/2". Not cheap, but sometimes you gotta "pay to play".

 

[ellis8500]

Here is chart with tensile and shear by bolt size and grade. A286 CRES is stainless steel. In the aircraft industry we referr to stainless as Corrosion Resistant Steel [CRES].

 

[ellis8500]

Here is a good primer about bolt grade selection.

http://www.billavista.com/atv/PDF_I...ners/Bolt Grade Info and Cross Reference.pdf

 

[choppinczech]

And I find that not all SS is the same. "Ordinary" SS is called 304 or 18-8. But ARP apparently makes SS hardware that is as good or better than grade 8 steel. My head hurts...

Here's what ARP says-

These gorgeous stainless steel bolts from ARP are rated at 170,000 psi to provide a substantial extra margin of safety over Grade 8 and other hardware. They are available in hex head or 12-point styles and a variety of lengths and sizes for use on cars, boats, and trailers.

 

[PotvinGuy]

What does is say on the head of your bolts? Most SS bolts are considered to be Grade 2 compared to steel.

My bolts are socket head cap screws (allens) and have no markings. They came from Albany County Fasteners, whose website says they are 304 (typical SS). I checked Totally Stainless, but their allens are described as "low strength." ARP doesn't make allens. Apparently no one makes strong stainless allens; wonder why? Guess I have to switch to hex head or 12-points if I want more strength. Or I could switch to chrome grade 8 steel bolts. I think I'll follow 2old2fast and drive it until something breaks. Which is how I address most problems

 

[2old2fast]

Looking at Bill's 2nd chart , a 3/8" bolt is in excess of 10,000 # shear strength . I don't think anything on my car will come close to those stresses... except internal diveline components....
dave

 

[ellis8500]

Under normal driving conditions the loads on fasteners is not an issue. It's when we have impact and acceleration loads that things will fail if they are undersized. Of course, if there is a large impact, i.e., very sudden stop against an immoveable object, stuff, including us, will likely break. So disregarding that, it's things like pot holes, curbs, etc that could cause undersized bolts to fail. In some areas, suspension mounts, it is not the shear nor tensile strength that is the issue; it is clamping force. A 3/8" bolt might be strong enough, but it will not provide sufficient clamping force to keep the parts from moving over time. But, as PotvinGuy proclaims, drive until it breaks. Just hope it's not the one that might cause a serious wreck.