Car came home on a flat bed Sunday. I was going about 70 mph, north bound on 580 about two miles from Patterson Pass. Four corvette club members were following me. As we came over the crest of a hill I heard a "bang", felt like I ran over something and then like I had a flat tire. I slowed down as fast as I could and pulled onto the shoulder. I got out of the car and checked the left side tires and all was well. Checked the right side and they were full of air as well. Looked under the car and the left side of my fiberglass spring was resting on the ground. At first glance it looked like the nylock nut had come off. Turns out it had along with about 2 1/2" of the grade 8 bolt. The club member following me said he saw something come flying out from under my car and then the left side tilted down. It wasn't untill I got the car home and up on jack stands did I see that the bolt had broken off. Measuring the right side against the left, there was 2 1/2" missing.

This morning I went out to see my mechanic and he said he has seen a couple of these after market 1/2" bolts break. The spring and bolts were installed about 10 years ago. Pat replaces the 1/2" bolts with 9/16" grade 8 bolts. He had all the parts in stock so I bought them and will replace both sides this weekend.

 

That's why I save alot of "original" GM bolts, such as these, thermostat housing, flywheel, exhaust manifold, intake bolts, etc. Seems as though these "hardware" type bolts just ain't as strong as "originals". Only time I've ever had an original GM bolt break and that was when it was frozen and it just "snapped" off. Never had a bolt break "in-service".

 

I have installed many fiberglass springs and they usually come with a "longer than stock" threaded bolt to allow for height adjustment. After adjustment, it is common for there to be several inches of bolt hanging down below the spring end. This excess bolt can take a hit because of its proximity to the ground... and the thread acts as a "fracture source". The GM bolt is only threaded for about the last inch and doesn't hang down in harms way like the aftermarket bolts. Your bolt could have taken a hit and fractured, or, the nut could have come off first and the bolt got damaged after the fact.

I usually cut the excess off after I have the height adjustment finalized, and double up on the nyloc nuts since they do not have a cotter pin like the original GM design.

(I also have extra bolts in stock in case I mess up.)

Tom