Well, that's a new failure mode

So I'm out autocrossing my XS-B class Miata (245whp, 245/40R15 BFG Rival S 1.5s, Xida coilovers, big RB sway bar) today and I'm really cooking with it. I get locked in a back-and-forth battle with another XS-B Miata and we're shaving half a second off each run. Come in from my second-to-last run and in the finish chute the brake pedal was hard as a rock. I had just been all over the rev limiter, and the pedal felt normal on the next application, so I thought maybe I'd just had no vacuum (car is supercharged). Drive it around the paddock and brakes feel more or less normal, hard to tell if I'm being paranoid. Go back up for my last run, get into the first slalom, which was done on the limiter in second, and near the end I go to hit the brakes and the pedal goes to the floor, then kicks up, then sinks again and the car kind of judders off to the left with a grinding noise. My thought is I just broke a caliper bolt or bracket bolt. I limp off the track and someone says the wheel is flopping all over. So 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. I jack the car up, take brakes off and find THIS.

Yeah, I've never seen that before. I've put 5 or 6 wheel bearings in the front of the car but always because they started making dubstep noises and were loose. Never a flange failure. My guess, the flanges were made too thin and from pure unrefined Chinesium and I put such insane loads on them that I broke them. 

By this point we had a crowd and the collective statement was "How the hell did you do that?" I guess if you're going to break, break in an interesting way. 

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.

The edge is only known by those who have gone over it.

Holy E36 M3.  That's somewhat terrifying.  

Mr_Asa said:

Holy E36 M3.  That's somewhat terrifying.  

Should have experienced it from the driver's seat, brother. That hiked the old heart rate. Did I mention I was an hour and 40 minutes from home, do not own a truck and trailer and this was my ride there and back?

NickD said:

Mr_Asa said:

Holy E36 M3.  That's somewhat terrifying.  

this was my ride there and back?

That was the part I was dreading hearing.  Imagine if it got somewhat funky on the track and then went while you were driving home?

Had a brake line give me a scare like that a couple years back.  Was about 2 miles off the interstate I had just been driving on, had been driving way over the limit. Was at a complete stop and waiting to turn and the pedal dropped to the floor.  Front left hose had just rusted through.  Had enough fluid and pressure to limp into a parking lot and call a tow truck.

What I find interesting about your part there is that it went out right at one of the two spots where I'd expect the weakest point to be, the threaded holes through the hub.  Always nice to know something intellectually, then actually see it at failure.

Good that it wasn't worse. Is that the factory part or replacement/aftermarket? 

Mr_Asa said:

NickD said:

Mr_Asa said:

Holy E36 M3.  That's somewhat terrifying.  

this was my ride there and back?

That was the part I was dreading hearing.  Imagine if it got somewhat funky on the track and then went while you were driving home?

Yep, I thought about that after the fact as well. I got lucky that it failed there. Although I blew the 5-speed up in it 900 miles from home and got back

I thought miata hub failures were fairly common with sticky tires.

There are a few companies that make stronger ones.  

wvumtnbkr said:

I thought miata hub failures were fairly common with sticky tires.

 

There are a few companies that make stronger ones.  

They are fairly common, but in my experience it has always been that the bearings themselves get loose/noisy. I personally have never seen one split the flange like that, nor had any of the serious Miata guys present. 

Rotor being trapped by caliper kept the wheel on the car. Brake Engineers FTW!

In reply to Mr_Asa :

It's actually required that all cars be dual hydraulic circuit (since the 60s) so that by design there's something left at the bottom of the pedal when you loose a line or caliper like that. Albeit the pedal will go a long ways down when it happens and I have seen people just assume there's nothing there due to reduced pedal height.

Yeash! I'm surprised you got by with only a gouge in the caliper.

Super common(albeit, not so much for autocross). Google "Miata hub failure" and click the link on Miata Turbo dot com. 

Edit:

https://www.miataturbo.net/race-prep-75/sm-weekend-failure-wheel-hubs-90331/

Timken had bad machining on their aftermarket hubs. When you replace, make sure the back side isn't machined to a 90 degree edge in an X pattern. It should be a smooth transition like a "J" rather than "L".

NermalSnert (Forum Supporter) said:

Yeash! I'm surprised you got by with only a gouge in the caliper.

The flange didn't break entirely. It had about a 1/4" segment still attached as well. So it was flexing around a bit but not entirely broke free

Yeah, there are some bad front hub flange designs out there. It's a little more difficult to make sure you're getting the right parts when you're shopping at vendors that are cost-driven such as Rock Auto - they'll change suppliers to shave off a dollar, so just because you got a good one last time is no guarantee you'll get a good one next time. Glad this one was caught in time.

I've never had a front flange come apart, but I have had a rear fail. Sorry Angry, the rotor wasn't strong enough for this one. You can see it making a run down the track when I'm at about 270 degrees.

Wow!

I’m trying to visualize how/why the brakes were acting like that. Was the hub coming apart pushing the disc into the rotor?

That is sop for Neon racers.  I've broken them in several interesting fashions.

In reply to CyberEric :

As the hub was flexing it was wobbling the rotor and pushing the caliper pistons in

CyberEric said:

Wow!

I’m trying to visualize how/why the brakes were acting like that. Was the hub coming apart pushing the disc into the rotor?

Massive knockback from the hub flexing like that is what it sounds like.

Some additional angles. I also took some measurements on them. The general flange thickness was 7/32" and the bosses for the studs were 11/32". It also appears to have filleting on the studs bosses. I have no clue what brand they were.

That's impressive, if you posted just the hub I would have said it was a roundy round asphalt car

Professor_Brap (Forum Supporter) said:

That's impressive,

As the gentleman with the spare hub said "If you're going to break, at least do it in a way that no one has seen before."

This was my first, and still favourite.  I thought I'd torn up a CV joint, or the clutch. The flange rotates on the hub quite nicely, but it doesn't come off.

Streetwiseguy said:

This was my first, and still favourite.  I thought I'd torn up a CV joint, or the clutch. The flange rotates on the hub quite nicely, but it doesn't come off.

I did the same thing on drag slicks. It's setting on my shelf. 

Professor_Brap (Forum Supporter) said:

Streetwiseguy said:

This was my first, and still favourite.  I thought I'd torn up a CV joint, or the clutch. The flange rotates on the hub quite nicely, but it doesn't come off.

I did the same thing on drag slicks. It's setting on my shelf. 

Looks like a quick bead with the MIG welder would have these back in service? LOL