Wheel stud failure

I remember testing some on an a torque wrench tester. Depeding on what style torque wrench, how recently it's been calibrated and how clean the bolts/lug nuts are makes a huge difference

 

I retorque after 100-200 miles, then again at 1k, 2k, 3k and again at 4k

 

Makes me want to get some spare studs since the dealer has rotated or swapped wheels 4 times already. I’ll have to figure out when I installed the spacers (maybe they were on before the dealer got their mitts on them, the factory studs)

 

It is hard to tell, but I don't see any necking. I dont see any obvious fatigue features (they could be there, but I dont see them). Some cup and cone features are there, but not totally apparent.

Most of what I see looks like tension failure, not much indicative of torsion failure (brittle or ductile).

Based purely on what i can see in the pictures, I am going with single tension overload of a moderately ductile metal. (Surely not pure brittle, but must be pretty hard material). Definitely a (hard) heat-treated or hardened material.

I am going to say either excessive torque, or reasonable torque with unexpectedly reduced friction (lubed threads). Not ruling out a metallurgy issue, but I bet not.

My 2 cents, worth exactly nothing...

 

i read these types of threads on various boards and it just backs up the whole some people shouldn't touch their vehicle when it comes to maintenance. amazes me how many unsafe vehicles are out there on the road with innocent families.

over torquing those studs is stretching them too far. you have probably weakened all of them with just throwing a breaker bar and your body weight on them.

set your lug nuts and every possible fastener to the proper tq. how hard is that?

 

The dark corner on the left looks like is where there was an imperfection (crack). It was there for a bit and the brighter bit on the right happened at the end. No shinny, shinny stuff, so it didn't rub.




As far as torqueing, I won't argue that torqueing to a specific spec is better, but it's definitely not a super precise measurement that it has to be. In reality, it's a range that you don't want to over torque past. The Toyota spec isn't going to be right at the edge. Otherwise, they'd have to get you a tool to change your tire with. Besides that torque wrenches aren't all that precise anyway. They are just a tool to get "close" to the amount of bolt stretch needed for a mechanical joint. If not using an impact, I'm probably under the spec as I never use a torque wrench and I don't hammer down on the tightness of the bolt. I go maybe a half a turn past snug. If it tightens up really fast, I stop.

I only say that because I kind of get the impression that many place too much emphasis on torqueing to an exact number or it'll fail. There is a point you don't want to torque past, but it isn't going to be the 83 ft-lbs or whatever the spec is.


For the OP, probably the use of a breaker bar and just over torqueing the bolt caused this. You really don't have to put your ass into it when tightening bolts (unless you have a 2 1/4 bolt or bigger and no hydraulic wrench). It probably started awhile back and just now failed.

 

On a different note, When removing either drum or caliper when on stud breaks is the bolt size of the two to remove either m 8 x 1.25 ? Or just caliper or rotor ?

 

I saw it, but just not convinced on the corner you mentioned, but hard to say without a bunch of pictures or seeing it in person.

Agreed on torque. I have built several homebuilt aircraft, and the only thing I have used a torque wrench on any of them is connecting rod bolts, cylinder hold-down bolts, and prop bolts... maybe a wing attach bolt occasionally....

That said, in the factories I have worked in, every bolt gets torqued with a calibrated torque wrench, even a good portion of philips screws.

 

In a manufacturing environment, you kinda need to "torque" everything because you have a variety of people tightening bolts and if you don't standardize it, you'll get people that will over tighten and under tighten and everything in between. Not everyone has spend lots of time with wrenches and torqueing bolts. After you break a couple, you kind of learn how much you can tighten a bolt.

Head bolts, rod bolts I definitely torque. Intake bolts.... nah. I've not done airplanes, but I'd probably torque a prop bolt for sure. I'd probably do the wing bolts too. Those would see lots of stress due to the nature of what they do.

 

See that dark little curved line in the lower right of this picture? It kind of spreads out with the thickness. It's a bit darker than the rest. That's probably where the crack started.

 

I lot of people don't realize that.
I think my CDI & PI wrenches are supposed to be + - 3-5% IIRC, from 20% of full scale to 100% of full scale.

Before spending the money on decent wrenches, I had two Tekton wrenches that were EASILY 25 - 30% off, brand new out of the wrapper. And they were getting rave reviews. lol

 

Bolt stretch is the best way, but not always feasible.

 

I've worked on some older GE Steam Turbines and the manual goes by "flats" of the nut. And it sounds funny, but when you realize that threads per inch correlates with degrees of rotation, it's a measure of bolt stretch. Probably more accurate than a torque wrench. I've even seen some boiler feed pumps that basically have degree markings on the nuts so you can turn the nut just the right amount to get the stretch.

 

Yep, for me I'm just gonna have to rely on decent wrench and clean hardware for anything I deem necessary of actually breaking out a TW to begin with.

 

Possibly, I havent seen enough bolts broke thru the actual thread to know what that will do visually. (I am used to tension failure at the thread run-out, adjacent to full shank).

One thing can see for sure is a very 'pretty' shear cone on the perimeter.
I do feel comfortable saying there was a large tension load on the bolt when it ruptured, and i dont think there was much plastic deformation before it broke.

Looks like that thing was heat treated or work hardened during manufacture towards the upper end of strength capability of the steel. Don't know what steel it was (and if it was wrong), but I would say it didnt accidentally miss heat-treat or anything like that...

(As always, just my random guesses...)

 

Static and dynamic friction coefficients are a bitch.

 

Now you're out of my pay grade, so I'm just gonna like your comment as if I know what you're saying and move along.

 

You probably know this stuff better than me, but that little dark line right at the threads makes me think it started there. If you look close, it kind of feathers towards the center. Since threads are where stress was applied to make the thread, that would be a stress point anyways more so if it was a cut thread.