3 busted lugs on one wheel
#16
Racer
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).
The following users liked this post:
Splitting Atoms (09-21-2021)
#17
Race Director
Thread Starter
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.
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.
#19
Race Director
Thread Starter
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.
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.
#20
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.
#21
Race Director
Thread Starter
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.
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.
#22
Racer
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.
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.
#26
Race Director
Thread Starter
#28
Race Car
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.
Don't the studs usually have a female hex so you can install them to the correct torque? Interesting that this set didnt.
#29
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."
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."