jandackson

Looks to me there may be some corrosion on the outer edges of that broken stud, indicating it was fractured for a while. No simple task to break one of these. From the shape of the displaced steel shown in the closeup, seems to have been a tensile failure( vs shear).

5CHN3LL

So, yeah, I'll be waiting for a nice new set of factory lug bolts to show up. That stud conversion set was from a reputable distributor, not eBay.

I've dodged two bullets with the 996 so far...while I love the simplicity of wheel changes with studs rather than lug bolts, the ones that don't break off unexpectedly are probably at least 20% cooler (confound those bronies...they drive me to insomnia).

Dunno if the distributor will want to do anything about it, but I'll let them know what happened.

Re: tensile vs. shear - until that third bolt popped off, the hub was still perfectly aligned with the wheel. There was some scuffing around the last two lugs (presumably because they were flexing, since the two remaining bolts were adjoining). I don't see HOW the first two lugs could have failed in any way except tensile. As far as corrosion, it's a CA car that has seen rain maybe five times since those studs went in.

wildbilly32

Original studs?

We need a metallurgist to tell why they broke. Is that rust pitting or metal impurities in the extreme fuzzy closeup?

5CHN3LL

I suspect there was a defect in a run of bolts, and that was the wheel that let go first (it's on the heavier axle, on my fat a$$'s side of the car - so it was the wheel with the most weight on it.

I haven't had those lugs installed for more than a couple of years. When I look back at some of the driving events and other drives I've done that could have ended in...well, let's just say I feel pretty damn lucky.

I'll take some better photos of the busted studs with my non-potato camera.

TonyTwoBags

Tensile as in torsional load? Beckham's tazer tells me you may have inadvertently over-torqued the aftermarket hardware - not exactly your fault but unfortunately your problem.

5CHN3LL

A recent over-torquing is an obvious suspect, but I have another theory.

The stud kit I ordered was supposed to have a machined hex socket so an impact driver could be used for installation. These are just rounded on the end, so I had to use two lug nuts snugged up together to be able to drive the studs into the hubs (by hand, of course - I didn't use a rattle gun or anything stupid for installing the studs).

I can imagine the stress concentrations in that specific scenario like I'm staring at the plot. This concentrated a butt-ton of strain onto what, a single turn of exposed thread. I think I screwed the pooch on day one.

jandackson

Hmm, I can see that scenario playing out. Jamming the two nuts together puts a tensile load on the bolt section between them. On top of that, the load is very concentrated oblong a short section of the bolt. Probably easier to cause yield than we think.

JayG

If you want replacement studs, one of the SDR members in Carmell Valley has a bunch. His car is Cupcake

Kalashnikov

Now we know identity of this driver....

Fracture

should probably pull that oil filter,...just to be sure

5CHN3LL

Here’s the failure point vs. the point where the two lugnuts would have met during installation.

garrett376

I've seen many broken studs over the years, but I have not yet seen a broken factory lug bolt. Has anyone else seen a broken factory lug bolt?

dan_189

This was a very near miss, lucky! Looks like the OEM bolts are the way to go.

Don't the studs usually have a female hex so you can install them to the correct torque? Interesting that this set didnt.

sweet victory

I will never use rennline studs (or equivalent) on any of my cars. Far too many reported failures.



All of the systems I deal with at work require specialized fasteners. Rennline states their fasteners are all black zinc 'coated.' This is rather misleading as it's not a coating, but rather a plating. During the plating process, high carbon steels are susceptible to a phenomenon called hydrogen embrittlement. Simply put, the material absorbs the hydrogen and it separates/invades the grain structure (small cracks) of the material. This makes it very weak - typically failing via fatigue...the failure analysis should just state, "cad jockeys/mechanics who thought they were engineers."

wildbilly32

WowOuch! Just glad the wheel didn't leave the car at high speed. That could have been...not good.

"You picked a bad time to leave me Loose Wheel..."(My apologies. It's late.)