Wheel stud fatigue...

[sergei]

I was doing the usual put the car on stands and blast it underneath (after driving on gravel and beaches) and do service at same time, when I finished I went to tighten the wheels (using torque wrench set to 85Nm), one of the wheel studs snapped.

The car is ST205, with standard wheels and toyota nuts. Studs where always covered in antiseize.

What really concerns me is that rest of the studs felt "soft" when tightening them to 85Nm. So I dialled down to 80Nm and placed a quote with Mark for whole set of studs...

How common is for studs to fatigue? I drive this thing fairly hard, but never over-tightened wheel nuts, kept them always lubricated with antiseize and always made tyre guys use their torque wrench.

Perhaps 85Nm is too high? Although repair manual states 103Nm, which seems too high.

Reason I am using 85Nm, is because that is what we use on race cars, and I had bad run with wheel studs failing before due to over-tightening (tire shops with ratchets).

[RS13]

Were they there before your ownership? Maybe they've been rattled gun'd up before?

[sergei]

I just gave it a good thought, and I believe because I use anti-seize on the studs it modifies friction coefficient, which modifies tension on the bolt (increasing it).

In other terms with anti-seize if I torque to 85Nm the equivalent dry torque will be a lot higher (proportional to friction difference between dry and with anti-seize).

So, using anti-seize on wheel studs is a bad move.

[sergei]

Were they there before your ownership? Maybe they've been rattled gun'd up before?

I had the car for 3 years. During this time it was rattled up only once - by muppets at compliance (basically when it got in the country).

[evil_si]

You are correct, when a bolt or stud is coated with anti seize, it increases the torque dramatically as the threads are lubricated,

I have a torque chart at work with the difference it makes, I will try and dig it out

[cat007]

You are correct, when a bolt or stud is coated with anti seize, it increases the torque dramatically as the threads are lubricated,

I have a torque chart at work with the difference it makes, I will try and dig it out

I would be very interested in this chart...
Don't suppose you could take a picture of it for us all?

[sergei]

You are correct, when a bolt or stud is coated with anti seize, it increases the torque dramatically as the threads are lubricated,

I have a torque chart at work with the difference it makes, I will try and dig it out

I would be very interested in this chart...
Don't suppose you could take a picture of it for us all?

it will be great if mods place it into FAQ section

[Mr Revhead]

Yes, would be handy!

[jondee86]

Some information extracted from an engineering forum....

That seems like a very low torque for a stud that large. We use
a program to determine torque based on size, thread and lubricant.
The numbers for 50% yield on a 1" - 8 tpi-UNC, B7 stud are as follows:

Dry - 1378 ft-lbs
Oil - 551 ft-lbs
Ni Lube - 413 ft-lbs
Mo Lube - 248 ft-lbs

These values are based on tests with new fasteners, in test-lab
conditions.

For any size and thread, the ratios are always the same. To get the
value for oil, use the number dry times 40%.
To get the value for Ni, use the number dry times 30%.
To get the value for Mo, use the number dry times 18%.

Theories will vary, but you can get the general idea

Cheers... jondee86

[sergei]

No wander why studs failed, I was applying 2 or even 3 times as much force than recommended.

[Burning Angel]

You are correct, when a bolt or stud is coated with anti seize, it increases the torque dramatically as the threads are lubricated,

I have a torque chart at work with the difference it makes, I will try and dig it out

using anti sieze doesnt increase the torque it increases the bolt stretch or clamping force for the same amount of torque applied to the fastener.

[Allister S]

You are correct, when a bolt or stud is coated with anti seize, it increases the torque dramatically as the threads are lubricated,

I have a torque chart at work with the difference it makes, I will try and dig it out

using anti sieze doesnt increase the torque it increases the bolt stretch or clamping force for the same amount of torque applied to the fastener.

Very good point this - I wonder how many people oil the threads on the strut lower bolts when tightening them as stated in the Toyota manuals (for certain Corollas etc. anyway). If torqued dry the clamp load could be much lower than required letting alignment change easily with a good bump.

I'll also clean off any anti seize I may have got on my Rally cars studs after fitting longer ones!

[sergei]

Got 19 out of 20 studs (last one on the way), will start replacing them and see if there are any visible cracks in them. I will also compare length with brand new one to see how much they have stretched.

[gmacrae]

yea dude, made that mistake before, oil or grease on a bolt or stud - amazing how much it reduces the friction. If you put it on all of them and torqued them the same, they're definitely stretched at least

[sergei]

I replaced front ones, definitely can see fractures.