9 replies to this topic

[Jeff Wasilko]

I switched cars part way thru last year, so in the off season I had my shop go thru the car and replace

all of the unknown wear items on the new car.

 

One of the things that was done was replacing the rear hubs and bearings. The parts were from Mazda. Everything

in the corner was new other than the knuckle itself.

 

Last weekend, the LR hub failed, spinning me in the wall at Thompson. Fortunately it was a light tap of the wall, so the car was easily made drivable again at the track.

 

My logs had me at 28 hours and about 1000 miles so far this year. I run in ITA, and time trial, so I run a mix of tires (nitto, ra1 and sm7).

 

In hindsight, I had a couple of odd spins to the left the prior weekend and the lap before it broke. I had written them off to driver error, but they might have been signs of what was failing.

 

I'm going to have the RR disassembled to see if it shows any signs of looming failure.

 

Both corners are being replaced with knuckles from Drago--thanks for getting the parts out to me so quickly, Jim.

 

I know we've seen some other front hub failures recently, but have folks seen the rears fail?

 

-jeff

[ChrisA]

Jeff, was this a hub failure/breakage where the wheel comes off, like some of the fronts we have seen? Or was this something different?

[Jeff Wasilko]

Yes, the wheel departed the car (and then passed me after I hit the wall).

[Keith Novak]

I had a rear hub nut fail last week.  I had been reusing hub nuts despite the FSM saying to replace them because in the past everyone had said they reuse them over and over and they never have an issue. 

 

I don't stake the nuts but I check them regularly with a torque wrench and they have never lost torque.  I think I had reused the nuts once or twice but the car has been through a lot like this little adventure a couple weeks before:

http://dougberger.ze...31f62#h2d0a9ba0

 

There was no sign of impending doom.  The car felt great with no vibration at all.  It felt like a blowout and then I saw my wheel pass me and launch into oblivion over the armco and down a hill.  Fortunately I was going straight and heading for a deep gravel pit used to stop motorcycles. 

 

I will stake them in the future and never reuse them.  As the FSM points out, they should be replaced because they are wear items and the cost of the nut is a lot less than the wheel and tire I destroyed, possibly the brake caliper, and all the suspension work that is needed now, not to mention losing a $3 trophy and half the weekend of racing.

[Ron Alan]

So Keith...in your case I assume the hub came out intact with one outer race and stayed with your wheel? Was it the right side?

[Keith Novak]

So Keith...in your case I assume the hub came out intact with one outer race and stayed with your wheel? Was it the right side?

Yes.  The outer part of the hub came out on the right side leaving the inner hub race in the upright. 

 

 

I thought about it being the direction of rotation where often you would find a reverse threaded nut however after some consideration I don't think it just backed itself off a full inch without the slightest hint of vibration involved.

[Ron Alan]

Exactly as I imagined if a nut were to come off. And the right side would be the logical side for this to occur quickly. So I wonder at what point the rotor broke to allow the wheel to go it alone??

[Keith Novak]

Exactly as I imagined if a nut were to come off. And the right side would be the logical side for this to occur quickly. So I wonder at what point the rotor broke to allow the wheel to go it alone??

It all happened at once from the driver's seat.  It was just after a very busy piece of course and then a 220* ish LH turn called The Carousel for obvious reasons. That would load the whole right side up.  Then you drop off a little hill and at the bottom it just felt like a blowout because that side just slumped and wouldn't brake.

Both the braking and steering inputs were completely normal up to the point where it just failed.

[Ron Alan]

 

Yes.  The outer part of the hub came out on the right side leaving the inner hub race in the upright. 
 

 
I thought about it being the direction of rotation where often you would find a reverse threaded nut however after some consideration I don't think it just backed itself off a full inch without the slightest hint of vibration involved.

To be correct...the whole hub came out with the bearing race still on it(this is how they come out when you change bearings)and what was left was the rest of the bearing in the upright.
Again...it's amazing how the rotor broke. Had the nut already come off and it took a corner or more for the stress on the rotor to finally break it?

[Keith Novak]

 

To be correct...the whole hub came out with the bearing race still on it(this is how they come out when you change bearings)and what was left was the rest of the bearing in the upright.
Again...it's amazing how the rotor broke. Had the nut already come off and it took a corner or more for the stress on the rotor to finally break it?

I don't think it could have been off long.  The preceeding series of corners really put the car through it's paces with sudden elevation changes and high G cornering.  If the nut had come off earlier, I think the wheel would as well.  I'm also pretty fast through that section and the car was not behaving abnormally at all.  It felt like a sudden catastrophic failure.