Rear end issues

[bobcowan]

Originally Posted by Soundkillr

I can tell you this...I just ordered the bmw brace kit for mine....it comes with a bolt smaller than mine so I would believe bdr does use the 14mm bolt

Mine is sheared as well...and I bought the kit that came with the bolt. So unfortunately I have to find a source for a hardened 14mm bolt...because the one in the kit is too small .

It had a hardened bolt in there to begin with. And that's why it's broken now.

I know I'm going to get a lot of flack for this, but I'll say it anyway. Hardened, grade 8/10.9 bolts are extremely strong along their length, and are great when you need high clamping strength. But in cross section they can be brittle. When subjected to lateral stresses, they will eventually crack and break. Which is what happened to you.

BDR tried to get around that by replacing it with a bigger bolt diameter. Sometimes that works. But here we are.

High grade bolts - 10.9, 12.9 - should only be used for high clamping strength in single shear if there is a locating dowel, or in double shear. Never in single shear in a high vibration environment. .

When I install the support bracket, I will use a grade 8.8. Which is about equivalent to a SAE grade 5. 75,000 psi is plenty in that application.

Carroll Smith once said, "There's no place on a race car for a grade 8 fastener."