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Old 08-04-2008, 05:50 PM   #1
gripen
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Exclamation 2 lug nuts broke while driving!

so i'm taking a leisurely drive on sunday
and all of a sudden i hear *thump thump thump* noise like i had a flat tire.
so i stop the car and my friend and i get out and look around the car to
see if we had any flat tires, all tires seem normal.

so we're puzzled and keep driving for another 100 meters when the noise gets
worse.

we stop the car and get out and upon closer inspection, we realized that
two lugs are broken off from one of the rear wheels!!!

so i stopped driving immediately and called the tow truck.
also managed to find this broken piece on the side walk.

it seems the lugs were about to break off one by one as we kept driving
seeing that the broken piece was found not far off from the vehicle when we stopped for the 2nd time.

one full lug is shown as a comparison, i couldn't find the other broken lug.


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Old 08-04-2008, 05:54 PM   #2
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WOW...

How does that even happen? Maybe they were loose
Or waaay overtorqued....?
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Old 08-04-2008, 05:58 PM   #3
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Or waaay overtorqued....?
that would be my guess..
it was towed to the last place that worked on my car
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Old 08-04-2008, 06:02 PM   #4
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I had this problem with my Mitsubishi Eclipse, Lugs/studs would snap off within a week of installing new ones. Came to find out that over-torquing and wheel spacers did it
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Old 08-04-2008, 06:35 PM   #5
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Or waaay overtorqued....?
That's what it is. Over-torqueing. You can see that the hex edges on the head of the bolt have been hammered by an impact gun.

FWIW, I hand torque in stages; first 40/lb/ft (with the car still on the jack and the tire wedged with a rubber wheel chock), then 55lb/ft (with the car lowered only slightly on the tire - just enough to keep it from turning), and finally 82lb/ft (with the car lowered gently and fully off the jack).

Even being careful like this, I still replace all lug bolts every year or two.

Scott
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Old 08-04-2008, 07:17 PM   #6
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damm.....
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Old 08-04-2008, 07:59 PM   #7
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holy sh*t!
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Old 08-04-2008, 08:38 PM   #8
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WOAH! Glad you're ok!

It'd be hard to blame anything but over torquing, as mentioned above. Too tight = too much stretch = failure under stress.

I guess we need to link this thread to the other one debating the necessity of properly torquing lug bolts...

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Old 08-05-2008, 12:42 AM   #9
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******** width="425" height="344">******* src="http://www.youtube.com/v/jv4m41viy4I&hl=en&fs=1" type="application/x-shockwave-flash" allowfullscreen="true" width="425" height="344">

but seriously shoot good thing the wheel didnt fall off
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Old 08-05-2008, 09:47 AM   #10
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I would want to take a good look at the wheel once it comes off as well. If it was only held on by a few lug studs the possibility of rounding out the remaining holes is high, in which case you would need a new wheel, and would be obligated to *****-slap the shop you took it to for using an impact to tighten wheels.
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Old 08-05-2008, 08:19 PM   #11
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The fracture surface on the broken bolt is showing signs of a fatigue fracture as indicated by the beach marks on the surface. There are also multiple cracks. What is interesting is that most of the fracture is by fatigue and comparatively little is by overload failure, so this may have been over-torqued once in the past and the rest was by driving. So I am not sure the last shop is guilty. It all depends on how long it was since you had it worked on last.
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Old 08-05-2008, 08:54 PM   #12
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******** width="425" height="344">******* src="http://www.youtube.com/v/jv4m41viy4I&hl=en&fs=1" type="application/x-shockwave-flash" allowfullscreen="true" width="425" height="344">

but seriously shoot good thing the wheel didnt fall off
HOLY CRAP! Not 1 but all 4, I think that was staged..................
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Old 08-05-2008, 09:04 PM   #13
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The story I heard behind the Mazda video was that the driver had just installed new lug bolts. They were the incorrect thread, yet he tightened and 'torqued' them into place anyway. Based on that story (true or not) the resulting failure was most likely not from improper torque - the fasteners were destroyed by cross threading on installation.

The actual collapse is pretty simple to explain - one lug fails, which puts its load on the remaining four. One of those fails, and so on until that wheel breaks off. As (based on the story) ALL of the lugs were damaged, the sudden and escalating increase in load - not to mention shock of impact - causes the catastrophic failure.

Now - if that story is false, other possible causes would be all (or most of) the lugs being loose, all (or most of) the lugs being otherwise faulty/defective, or some elaborate plan to destroy a nice car for YouTube fame...

The first story sounds the most plausible to me...
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Old 08-05-2008, 09:15 PM   #14
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Are these OEM or aftermarket?
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Old 08-05-2008, 09:26 PM   #15
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That's what it is. Over-torqueing. You can see that the hex edges on the head of the bolt have been hammered by an impact gun.

FWIW, I hand torque in stages; first 40/lb/ft (with the car still on the jack and the tire wedged with a rubber wheel chock), then 55lb/ft (with the car lowered only slightly on the tire - just enough to keep it from turning), and finally 82lb/ft (with the car lowered gently and fully off the jack).

Even being careful like this, I still replace all lug bolts every year or two.

Scott
Even being careful like this, I still replace all lug bolts every year or two


Wow - that's wow.
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Old 08-05-2008, 09:49 PM   #16
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so i got my car back today,
they did cover the work at no charge

what they say is that the lugs were torqued to spec by hand on the ground
and it is a strict rule to do so

they suspect that from the time the car was in the shop
and last sunday, a thief tried to steal my wheel and loosened 2 bolts and ran away
when possibly the thief realized somebody coming by

as a result, the loose lug rattled around in place until it broke off while driving.
no rust on the broken piece indicates that it's a sudden break,
if it was rusted, that means it's been slowly breaking over a long period.

so i'm not a 100% sure what happened, there are many many possibilities
but it just leaves a bitter taste, and it's just scary to think that somebody could sabotage my car while
it's parked and i could get seriously hurt as a result under certain circumstances.

i'm just thankful my friend and i weren't hurt and no serious damage was done to the car.
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Old 08-05-2008, 10:05 PM   #17
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they suspect that from the time the car was in the shop
and last sunday, a thief tried to steal my wheel and loosened 2 bolts and ran away
when possibly the thief realized somebody coming by
This is the best explanation they could come up with? I guess it's not impossible, just highly unlikely...
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Old 08-05-2008, 10:42 PM   #18
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so i got my car back today, they did cover the work at no charge
what they say is that the lugs were torqued to spec by hand on the ground and it is a strict rule to do so
they suspect that from the time the car was in the shop and last sunday, a thief tried to steal my wheel and loosened 2 bolts and ran away when possibly the thief realized somebody coming by
as a result, the loose lug rattled around in place until it broke off while driving.
no rust on the broken piece indicates that it's a sudden break,
if it was rusted, that means it's been slowly breaking over a long period.
so i'm not a 100% sure what happened, there are many many possibilities
but it just leaves a bitter taste, and it's just scary to think that somebody could sabotage my car while
it's parked and i could get seriously hurt as a result under certain circumstances.
i'm just thankful my friend and i weren't hurt and no serious damage was done to the car.
The story I heard on the RX7 in the video is that he used 1/2" lugs. Mazdas take 12x1.5, but the evil thing about that combo is the 1/2" will thread and tighten, but it's a little too big, so as soon as it sees any real load, the lug will just skip along the stud and come zipping off. If you're used to wheel changes, you'll feel that the lug wobbles a tiny bit as it's threading down, but it takes an experienced touch to realize something's not quite right.

OP, it's possible that someone got halfway done stealing your wheels, or someone loosened the bolts intentionally. Anyone take out any life insurance policies on you lately?

Were the other 3 lugs still tight and the wheel still tight against the brake rotor? If so, then the shop's theory doesn't sound true. If only 2 lug bolts were loosened, I can see them backing themselves out, but they're not going to break unless enough lug bolts come loose to let the wheel slap against the lug bolt and exceed it's max load.

You can take 2 lug bolts off your car and drive it around for a while on 3 and not have any issues. I don't recommend it, but 3 lugs WILL hold the wheel in place under normal conditions. So there's no reason for 1 lug bolt to break just because it's loose as long as the other 3 or 4 are tightened properly.

I think overtorquing is what killed the one in the picture. As someone else said, the ripple effect in the grain structure of the lug is indicative of a fatigue failure. And the edges of the hex on the broken one have clearly been abused a bit more than on the unbroken one. Also, the mating surface of the broken one shows signs of a lot more radial friction than the unbroken one.

That doesn't mean that the shop that worked on it most recently overtorqued them. But that is the most likely scenario.

Anytime an impact is used to tighten lugs, it has to be done carefully, with the impact turned to a low setting so that the final torquing can be done by hand with a properly calibrated torque wrench.

Hope this helps. Good luck.
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Old 08-05-2008, 11:15 PM   #19
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SO many shops will use impact guns lug nuts, it's pretty pathetic. I had a shop use an impact wrench after I bought new tires and had to go back because I couldn't get the bolts off. They loosened them and I requested they torqued them by hand. They used the "torque sticks" on their guns which still are terrible. Laziness and stupidity.......
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Old 08-06-2008, 03:21 AM   #20
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are the wheels aftermarket or oem? are you running spacers? because i've seen that with a wheel that was running spacers. the spacer expands and contracts at a differing heat rate than the wheel..and loose lugs..and then cracked lugs. if the wheel is wider and there isn't much of the lug getting threaded, it could shear like this( i would think).

but my first guess was that they were over torqued.

my third guess would be they put the lugs on and they forgot to do that ground torque to that one wheel. so all the lugs are loose and results in wheel shimmy and lugs breaking. i would look closely at the area where the lugs sit like previously mentioned. if they are not connical, you're going to have vibration issues as that wheel is toast.
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