Well, that's a new failure mode

It looks like fatigue fractures that started in the threaded rotor removal holes.  Are there any clamshell markings on the fracture surface near those holes?

I sent the original picture to a good friend of mine who is an expert in metal failure.  He thinks metal fatigue starting at the hub.  

Good job and one for the wall of shame!.

Stuff like that is why I moved from driving to an autox and began towing to the autox :)

 I had a left side cv shaft seize in our luckydog K20 civic car into turn 8 at Mosport a couple weeks ago....fast right hander and the car only really wanted to go left.

 Same puckering you experienced just a bunch faster.:)

Because I've done a bunch of them, and so had the guy lending me the tools and part, we had the car up, apart and diagnosed, repaired and on the ground in literally under 20 minutes. As we were letting it down off the jack, a guy paddocked next to us went "So, it can't be fixed here?" "No, it's fixed already." "What? That fast? I thought you guys were just diagnosing!"

I've personally seen it happen twice at the track.  Once during an HPDE and once during a race.  Always surprising!

I'm curios about what wheels you were running, how they fit the center of the hub and how the back side distributes the load across the flange.

on old VWs the splines in the rear drum  will grind away in the hub if the center nut is not tight ,  or if its a bad quality drum

then the car will not move but the stub axle will spin in the drum , 

it does take a long time for this to happen , so months of neglect !

In reply to APEowner :

I'm running 15x9" Konig Dial-Ins. I am running center bore spacers to make them fit the hub perfect. The back side looks like this (Not my wheels, but photo I found online)

@ the OP did you by chance use a puller on that hub at some point?.  It i interesting that the cracks radiate from the threaded holes.  Almost makes me think that if a puller was used it point loaded and caused small cracking at the threaded holes and they just kept getting bigger and bigger and finally failed.  Is there any rust in the crack anywhere or is it a fresh break.

In reply to dean1484 :

Just looked, no rust anywhere in the crack. And, nope, I have not used a puller on these ever. I had them off about a month ago to put the ARP studs in, and I just unbolted the spindle nut, wiggled it a little, and it slid right off. Then I pressed the new studs in and out and reinstalled.

dean1484 said:

@ the OP did you by chance use a puller on that hub at some point?.  It i interesting that the cracks radiate from the threaded holes.  Almost makes me think that if a puller was used it point loaded and caused small cracking at the threaded holes and they just kept getting bigger and bigger and finally failed.  Is there any rust in the crack anywhere or is it a fresh break.

 

  

I dont think I agree with this. To me the crack started in the middle and radiated outward. It stopped at the two holes, but would have kept going at the other two ends. 

Slippery (Forum Supporter) said:

dean1484 said:

@ the OP did you by chance use a puller on that hub at some point?.  It i interesting that the cracks radiate from the threaded holes.  Almost makes me think that if a puller was used it point loaded and caused small cracking at the threaded holes and they just kept getting bigger and bigger and finally failed.  Is there any rust in the crack anywhere or is it a fresh break.

 

  

I dont think I agree with this. To me the crack started in the middle and radiated outward. It stopped at the two holes, but would have kept going at the other two ends. 

Agreed. The threaded holes see virtually no stress in an un-failed hub. Hell, the wheel doesn't even make contact in that area. It turns out that round holes are also better at stopping cracks than they are at starting them..

Speaking as someone who has in a past life memorably been responsible for designing and stress analyzing a hub for use in NASCAR, in this design the stress is almost entirely where the stud pad transitions in the the hub body. That's also why it is appreciably thicker there...Except that it unfortunately has a cut back with a huge stress riser rather than a smooth radius transition. That is the only reasonable place for the crack to have initiated on that hub. Notice that the cracks also propagated to the same point in the other two quadrants, even though there are no holes at either crack intersection. So it would have started directly inboard of the studs, and propagated both directions (mostly) tangentially from there.

Did you happen to have a spare hub?  How'd you get it fixed and back home?

NickD said:

SSo another Miata driver says he thinks the wheel bearing failed and he has a NIB spare that has been carrying for 3 years and the tools to do it. ...

Car was fixed in 15 minutes but I missed my last run, handing the position to the other XS-B Miata. Also ground a gouge in my new Wilwood caliper. But no real damage other than my nerves. Guess I should replace that other one before next weekend.