I had a left rear wheel hub snap on me after exiting a right hand 1.4G turn at the track last week. No warning. If you heavily track your car I'd consider these a wear item and proactively replace them at some point... It could have been ugly. When these break it causes about $5K in damage as it wipes out the brake rotors, upright, axle, etc. Not cheap...

[url=https://flic.kr/p/yuMdAv]

[url=https://flic.kr/p/za9GRV]

 

No damage to your car I hope.

 

Wow, thanks for an eye opener

 

Not really. Besides the hub, the upright and wheel rotor was scratched from where the hub made contact after breaking. I am replacing everything in the rear on both sides with 997Cup and RSR parts to beef everything up. New uprights, bearings hubs, axles, rotors, thrust arms, LCAs toe arms, etc. Might as well while in there...

 

wow nasty!
any signs of excessive heat build up from a bearing issue?...think the ~cup car spring rates may be partially to blame
'new' hubs seem to have a different design but no change made to the bearing transition area...(hard area to 'beef-up')..the Cup/RSR/R upgrade is probably a smart move on many fronts...

 

Glad you did not get hurt and the car is fine! Impossible to check but I wonder if the axle was torqued to proper spec. seems very hard in my mind as the splines of the axle pass through the point of failure so that should act like one solid piece of steel with the axle nut clamping it all together at 325 ft lbs of torque.

 

No signs of heat or a bearing issue. I think this is just a simple case of metal fatigue. Just imagine how much force gets put on the hubs, especially in the rear where you not only have the engine twisting torque acting on the hubs but also the constant lateral Gs that are acting on the hub. I regularly see +1.4Gs on my data logger which translates to close to 3000lbs of lateral force and that can easily increase from loads imposed on the hub as the car comes off of apex curbing down onto the outside wheel. Combine that with a 12 year old part that had seen 100hrs of track use and it's no wonder. I believe the 997 hubs are a beefed up design from the pictures I've seen.

 

Tim, axle nut was torqued properly and checked frequently. 340Ft.lb is the spec if I'm not mistaken. That's the first thing we checked after the failure. As I mentioned in my post above, I think it's the combination of a 12 year old part constantly being subjected to great lateral loads. Our track has mostly right turns and it was the heavily loaded left rear that failed. Even after it cracked all the way around, it was still sandwiched together by the axle nut but the axle torque was now transferred to the hub by the last 1/4" of the splines as opposed to the full +1" or so. The splines finally failed as you can see in the close up picture. I exited a hard right hand turn and as I leaned into the throttle the RPMs just shot up. I thought I lost the gearbox but it was essentially the same as loosing an axle. The LSD obviously couldn't cope with it. No worries though, got some trick RSR and Cup stuff going in. Car will be better in the end.

 

Sorry to see the breakage -- but looking forward to seeing the upgrade path!

 

Check/inspect everything before and after tracking. Every time.

 

Yikes, I have been considering this for a winter mod. This pretty much settles it. Probably going to get new rear LCA and UCA as well. Have heard of those failing too. The rear suspension on our cars take a beating. Especially with the heavy weight and rear bias.

 

Are you trying to say you would have caught this before it happened by looking at the part? X-ray vision? The part just snapped..

OP - Glad you / the car are O.K.

 

Exactly. No way to check the hubs. That's why I'm saying swapping them out proactively and doing the bearings at the same time is a wise choice.. Cheap insurance.

 

Well, the car is back together. I ended up taking this as an opportunity to beef up everything in the rear suspension. I put in new uprights, new bearings, and new hubs. We put in 997GT3 hubs which are indeed thicker than the 996TT hubs. While at it, we swapped in all new wheel studs. Additionally, I ended up installing PMNA 997RSR lower control arms. These are really slick as they have an inner monoball along with solid adjustable thrust arm bushings and a super beefy replaceable outer monoball joint. Since this was one of those "while in there" moments, we also ended up putting in PMNA 997Cup toe arms. These are really nice as they employ a "pinch" collar on both ends to lock in the adjustments. This makes alignments a breeze compared to the jam nut arrangement. Finally, we put in new 997GT3 thrust arms and new 996TT driveshafts. The last piece of the puzzle was the install of 997.2GT3RS brake cooling ducts. This version is much more efficient compared to the old 6GT2 units as it get much more air to the rotor along it's full annulus. All in all, this was a bit of an unexpected project but I am happy to know I have a much stronger set up going forward and can feel confident pushing the car hard again. Just wanna say that this upgrade would not have been possible without the assistance of my "skunk works" shop that suggested and sourced all the necessary parts for this project.

New hubs with new studs. Note how the GT2 heat shields had to be trimmed to clear the RS air duct

997RSR LCA. Note the outer monoball and the RS air duct.

997GT3 thrust arm air guides. Note the belly pan NACA duct exit in the wheel well liner and the 997Cup caliper studs

Rear view of the RS brake ducts and the 997Cup toe arms

Close up of the pinch bolts on the 997Cup toe arm. Note the use of a double jam nut arrangement instead of the stock single nut.

Close up of RSR monoball

 

911porn!