Cory9584

Is 18.8 stainless as strong or stronger than 12.9 steel? I heard stainless tends to be softer, is this true? It would be nice to use stainless in a few places where you really need it but i dont want to give up strength.

jerome951

Stainless is significantly weaker than 12.9. I wouldn't recommend stainless in any hi-stress applications. A good coated 12.9 (like the factory stuff) will be a better choice.

PCinDC

Agreed, a heat-treated 12.9 fastener is far stronger in tension than 18-8 stainless. Also, a zinc plated 12.9 grade fastener has most of the corrosion resistance that stainless offers. One important note is that zinc plated fasteners used in high heat environments can suffer from hydrogen embrittlement after many heat cycles. Zinc dichromate plating solves this problem.

Cory9584

The factory bolts are 8.8. And thanks for the replies, i guess ill be using 12.9 everywhere

Tom M'Guinn

There are a few 12.9s in there -- girdle nuts, balance shaft bearing bolts, etc....

TF

While we are talking about bolt grades I have a question. I am installint Bilstein coil overs without t bars so I want to ungrade the 8.8 lower shock mount bolt. I know 10.9 should be better but am worried that 12.9, even though it is stronger, may snap sooner. Then I was tols that stainless might work better. Any suggestions???

THANKS
Tom

PCinDC

Tom, The best option for the lower shock mount is this piece from Racer's Edge: http://www.racersedge-inc.com/racers...?open&id=7.3.6
I've also seen some knockoffs on ebay for a bit less $$$. Ebay ID of seller was fastech or fastechracing IIRC.

jerome951

Stainless isn't a good choice in hi-stress suspension applications, especially in single shear like you're describing.

As a datapoint, I've been running 10.9 bolts in the same configuration you mention for 2 years with no problems. I spin them on occasion looking for bending but have yet to see any. I carry a bunch of spares to the track in case one breaks but have yet to use them.

ENGINEERMAN

I am running grade 12.9 hardware on all suspension bolts. Garrity at Motorsport set me up with the entire set including bolts, nuts and washers. So far they have only been in for a couple of months so not much data to provide but I see no reason to be concerned that the 12.9 is too hard, i.e. brittle for this application. Garrity recommended this grade as well based on a lot of practical real world experience. MS is a small outfit but he is a good guy and will discuss your objectives with you and then make recommendations.

Good luck!

MOTORSPORTINC.
2121 SO. RICHARDS ST.
SALT LAKE CITY, UT 84115
801-487-6733