Sheered off lugs while driving

I worked for the State of California, in their Highway Dept.
We had a fair sized Fleet of trucks.

We used a Tire Shop, that repairs & replaces tires on everything from trailers to pickup trucks & everything bigger, including Earth Moving Equipment.
Sometimes the employees would not check the setting on the Air Impact Guns.
The previous vehicle that had a repair may have been a semi truck & i would drive in with a 3/4 ton pickup, if the employee did not check the pressure setting, even if the guy was quick when releasing the trigger, he had already stretched the threads or sheard a stud right off.

That shop never accepted the blame, they just said that the Lugs were old & stressed.

Our Equipment Manager would cuss under his breath & have one of his mechanics replace the broken stud.
When there is only 1 place that works on Heavy Tires, it is not prudent to stop using that supplier

They were most likely over torqued at some point, Understand too that the torque specified in most shop manuals is a non lubricated value if you apply oil or anti seize and torque to the specified value you will be over torquing the stud conceivably enough to cause this type failure.

You should be able to measure them with a Vernier Caliper but you would have to know the flange thickness of the hub and the stud length in order to detect stretch.

to the OP why would you not just replace the studs instead of he entire hub?

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RamDiver said:

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Maybe the buttons on his phone / PC sheered off.

rneal55555 said:

They were most likely over torqued at some point, Understand too that the torque specified in most shop manuals is a non lubricated value if you apply oil or anti seize and torque to the specified value you will be over torquing the stud conceivably enough to cause this type failure.

You should be able to measure them with a Vernier Caliper but you would have to know the flange thickness of the hub and the stud length in order to detect stretch.

to the OP why would you not just replace the studs instead of he entire hub?

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Lubed wouldn't stretch a bolt if you're using a torque wrench. That would most likely only be 10 % increase on bolt stress. Now tightening with a 600+ ft lb impact gun is most likely the culprit. And if someone did that they most likely didn't start the lugnut by hand, the put the nut into the socket and ramped the gun up to full speed before ramming it onto the lug.

I would agree with the air guns being the cause. If you have road service it's guaranteed that gun is cranked to semi truck. I do the torque wrench.

indept said:

Lubed wouldn't stretch a bolt if you're using a torque wrench. That would most likely only be 10 % increase on bolt stress. Now tightening with a 600+ ft lb impact gun is most likely the culprit. And if someone did that they most likely didn't start the lugnut by hand, the put the nut into the socket and ramped the gun up to full speed before ramming it onto the lug.

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I de-rate the dry torque setting by 20% when I lube my nuts.

You will have to ask an Engineer about the stretch coefficient of wheel studs.

A good friend of mine likely has the education and experience to answer these questions, I'll see if he's interested in commenting.

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