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Discussion Starter · #1 ·
So the weather in Madison this weekend has been as warm as it's been all year. Timing seemed right to take off the snows and put the stock wheels and tires back on. I got everything switched out and I was tightening the lugs on the right rear wheel, and POP! Broke a stud right off. Needless to say I was very surprised considering I'm not a buff guy by any means and I was using a torque wrench set at the 100 ft/lb rating given in the owner's manual.

I'm sure this has happened to others, but I'm just surprised to have it happen on a new car. Hopefully the dealer can get me in tomorrow to get it fixed.
 

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Discussion Starter · #3 ·
Lubricated. Just a bit of WD-40 on the studs in between taking off the wheels and putting the others on.
 

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Usual, 100 foot pound is near the high side for a 12mm stud but its the spec and should handle it no problems. Torque wrench accurate?, they need calibrating from time to time, Snap-on suggest around every 12 months for regular use, say as a Mechanic. Last time I had a torque wrench calibrated it was out by nearly 20%, it hadn't been checked for over 5 years.
Perhaps corrosion or thread damage caused it to fail.
 

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70% increase in tension on the threads with antiseize or light oil... be careful!
You can't lube threads and torque them to dry specs. It is a random guess but usually 30% less torque is a safe bet.

Still shouldn't break a stud without some serious torque. Though I agree I don't feel comfortable torquing those little lugs to 100 ftlbs. Seems high imo. But think about the monkeys at the tire shop that pound them on and off without a torque stick all the time. They tend to survive well, specifically as the cars are all brand new. It is possible they got overtightened and streched somehow previously.
 

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Did the lug nut come loose from the stud after it broke off? It could of been stripped, especially if had this done and they started them with a gun, I had this happen at a shop, stripped 4 or 5 on the car......

Could also of been over torqued at the factory when the stock wheels were first put on and finally failed as well. Though they are supposed to be done right I always check torque, air pressure, alignment, immediately when buying a new car. I thought these were really tight so set them at my normal alloy wheel rate of 85lbs, I guess I should of looked it up so now I will redo them again.

I torque in sequence as the lug pattern determines and at least two passes, half then full, to ensure seated properly. Also best to torque with the wheels off the ground or if not able to on fronts on a rear wheel drive I lightly touch the tire to the ground to keep it from rotating.

The only car I have seen torque specs so high was on my Vettes, I used ARP studs on them and looking into studs for this car as well.

Rick
 

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Discussion Starter · #8 ·
I didn't know about the increased torque when lubricating the studs. Thanks for the tip.

The lug and the stud came out together after it snapped. What's odd is that now that I've looked at the stud that came off, it's narrower at the end that broke. The threads are farther apart too, like it was stretched. Something I wouldn't expect without heat or an extreme amount of force. I'm going to try and get a pic.
 

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Discussion Starter · #9 ·
Screw Auto part Nut Hardware accessory Household hardware

Not sure of the quality of the pic, but see how it's narrower on the right side of the stud?
 

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Certainly not stripped as that would be easy to see and the stud would be stuck in the nut.

Looks like it was broken in removal, not install as it would be compressed not stretched.

Overly tightened could fatigue, stretch, it etc a bit then when removed it gave way, not instantly but during a few turns it appears.

Or just a bad lug bolt, it can happen.
 

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The stud has been over tension, probably with a Impact gun or overloaded, like something has tried to pull the wheel off, unlikely. The deformation where the diameter has been reduced is called Plastic deformation. Bolts or studs are designed to stretch, they act like a spring keeping the joint clamped together. They are tension to around 75% of their Yield point or Proof load, that's the point where the bolt or stud deforms and still returns back to it original shape.
As someone pointed out lubricating the thread can has significant influence on how far the bolt or stud stretches verse the tension.
WD-40 is fine as a light lubricate and makes little difference verse a clean dry thread, imo
 

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as torque is just an easy way to measure bolt stretch it was factually over tightened as some point to deform it that bad. It would have been easy to feel that much stretch by hand so i agree likely an impact related failure.
 

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The stud has been over tension, probably with a Impact gun or overloaded, like something has tried to pull the wheel off, unlikely. The deformation where the diameter has been reduced is called Plastic deformation. Bolts or studs are designed to stretch, they act like a spring keeping the joint clamped together. They are tension to around 75% of their Yield point or Proof load, that's the point where the bolt or stud deforms and still returns back to it original shape.
As someone pointed out lubricating the thread can has significant influence on how far the bolt or stud stretches verse the tension.
WD-40 is fine as a light lubricate and makes little difference verse a clean dry thread, imo
This man knows his fasteners!
 
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