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Be Careful With S550/GT350 Wheel Studs

I have a confirmed stud breakage on a GT350. The member can identify himself if he wants but here's the proof. This car has been driven at 13 track days. The manual states the torque specification is 150 ft lbs + or - 15 ft lbs. Torquing to 135 is within spec and I'm not going beyond that on my car. The good news is Ford Performance and ARP have finally released longer and stronger wheels studs with nuts to match so that should solve the problem.

@Moto
@tim

3D8F2B1C-4EDB-4396-9665-258010741C4B_zpseupsiik9.jpg
 
The break is at the end of the thread which would be a stress riser. I'd like to know more about this. Cordless impact, brand of torque wrench etc. Poor practice by dealer during PDI, did they ever run not to spec. I run the ARP 1/2" to 125. What tire? I had my wheels torqued with stock studs and after one session they all got some turn out of them at my first track day. Fronts see a lot of heat from braking.
 

steveespo

Lord knows I'm a Voodoo Child
Moderator
3,799
1,347
Exp. Type
Time Attack
Exp. Level
10-20 Years
Cookeville TN
By the looks of those rotors it is possible that the lugs were being removed hot off the track. I have galled even ARP studs and many lug nuts being impatient and loosening the lugs while still track hot. You have to wait until they are cooled off enough to keep a finger on them. Wasn't said if this happened loosening or tightening.
Steve
 
It's been 8 years since any failure analysis training but the rotor hat above the left stud. The wheel witness mark right below the N and the T; that shiny spot in the witness mark is indicative of fretting (movement)

The left stud looks like it failed from a torsional stress fracture (twisting-galled threads etc) WD-40 is your friend here.

The right stud is tough to tell from the picture but it looks like a possible lack of torque failure.

The stud below the right one looks fractured when I zoomed in.

What looks like a plastic hub centering ring for a wheel causes me not to elaborate further going off a picture on the interwebs. I assume this is not factory.

The spec is 150, torque them to 150... By hand and use a light thread lubricant to prevent galling and corrosion. Do not use chlorinated brake cleaning products around critical fasteners, they have been proven to cause a type of 'embrittlement' in certain environments.
 

DEye

You can't get there from here...
What kind of "light thread lubricant" do you suggest? A bit of anti-seize, or ??

There have been some thread "care" discussions on some other forums and the "professional" Eng. input was not to lubricate wheel stud, clean dry is the way they were designed...

I'm just relaying what was the "official" word was vs. armchair quarter back.
 
66
61
Exp. Type
HPDE
Exp. Level
5-10 Years
Minnesota
Interesting conversation and anecdotes. Good to hear others experiences. I haven't torqued past 120# on wheel nuts for the past 3 years of tracking. Especially on my flow forged aluminum wheels with slicks. I always check torque after the hubs have cooled from track temps and have never had an instance of the lugs loosening. I use FP pass thru lugs on stock studs. Maybe I'm living on borrowed time? But never any issues and no evidence of stress that I can see.
 

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