stout

Don't want to get into a "Porsche should have" or "Porsche should not have" debate. Frankly, I have my opinion but it's irrelevant. Porsche did.

I hang out here with some regularity and have grown fond of a number of you — which is the only reason why I am posting this. Certainly, it won't make friends with some camps. I just want to say, please follow the factory GT3/GT2/Turbo centerlock instructions to the T if you run a car with them. Savyboy (and others) have posted on this extensively, as have several track guys who have run without issue. Please also consider additional safety gear, and pick your risks wisely.

Last weekend, a race shop near me had an immaculate GT-class race car (built out of a street car, to a very high standard with ALMS parts) go upside down at high speed in a big way. Saw the car on Friday and it was perfect. Saw the car on Monday and it was a mess. Every body panel affected, windshield long gone, and a crack in a very big frame rail. Fortunately, the car had an over-built roll cage and the driver walked away.

Cause of accident: Failed centerlock stub axle. Theirs was the proven external-style setup, and this is an experienced race team (IMSA and FIA 962, Indy Lights, ALMS, NASCAR, etc.) that very much knows what it is doing and has run enduros with this car. Could they have made a mistake? Sure, but I kinda doubt it given their track record and expertise. I've known the shop for more than ten years, and would not hesitate to go out in a car they have prepared. At all.

Their analysis: They think the steel axle just might have timed out. Unlike GT3 Cups, this car doesn't have the luxury of specified time limits.

Cost to fix the car (my wild guess): $50,000-100,000.

Cost had a similarly fast GT3 gone upside down with no cage: the driver's life?

The team's solution: Replace the stub axles with brand-new parts and hope this doesn't happen again...or move to five-lug hubs. Only thing stopping them from the latter is one particular enduro race. Every other race that the car runs, they say, would be fine to do on five-lug hubs. Tire changes would be fast enough, and they'd prefer to have the safety margin. But I suspect they will stay with the racing centerlocks given the car's usage.

Look, I hate the idea of discouraging you guys from having a ball out there in your Porsches, but I have to say the carnage around the upper bars of that car's cage got me thinking pretty hard about what precautions I take. A well-driven GT3 RS isn't all that much slower than this car, and a GT2 RS in the right hands might turn a couple of laps every bit as quick.

Yes, what we like doing is inherently dangerous, but there are some risks we can minimize.

pete

CRex

Very well said. One cannot butch one's way through wheel change procedures and blame Porsche for the outcome. It's the driver's own responsibility to check torque the wheels off the ground and check the splines at EVERY change.

I have my opinion about Porsche's decision to use something this error-prone in street cars. The complex (but not complicated) procedures with no room for error is a recipe for user error.

911SLOW

Pete eloquently gave the i^]%]'s award for 2012-13 (the third consecutive year) to the £~^|!#(s) in the marketing and "research" dpt that had the brilliant idea of implementing "race wheels" to a perfectly fine street car.

It's 3am here mind you. : )

senna

Thanks for the feedback. It makes me think I need to pay more attention to the wheel change, and maintenance of the parts. I may add a visual inspection request by a Porsche Technician every time I take the car for fluid changes as well. Another set of eyes wont hurt. If I continue to track the car, I may add a front cage too despite of what others say.

paver

That...and there was no performance benefit that I know of.

mdrums

Thanks for the thoughts and feedback Pete. I follow Porsche's tech manual on installing the street center locks by the book and also taking the center locks apart for cleaning and greasing the certain internal parts. I'd also like to thanks Savyboy for posting these tech papers from Porsche and thank Izzone for showing the center lock install procedure in person.

With that said I'm extremely concerned about the durability of the center lock hub on the street cars due to the known center lock hub failures that have cropped up. I've taken a step back to re-evaluate my DE participation. I'm taking a real hard look and thoughts about using my GTS with street center locks in this manner.

Izzone

The fancy harness bars people use won't save you

Porsche makes a proper cage that I don't have problems using in the street, best mod I have done

DRPM

I had my car in at my P dealer this week and kindly requested and received a full (dirty) hands-on tutorial from their lead technician on removing and installing the CL's on my car with my new Precision Instruments 3 piece torque wrench.

The devil is in the details...

mdrums

Did he show you how to take apart the inner guts on a center lock nut?

This step is important to maintain the center lock friction parts on the inside to insure proper torque when tightening.

FFaust

So, what are the time limits on the cup car steel axles?
Could preventative NDT inspections catch cracking before catastrophic failure? Especially since steel does not fatigue as "discretely" as aluminum.
Sounds as though following Porsche's centerlock instructions to the T would not/did not prevent this type of failure...?

Snowboarder54

Pete, as usual well stated! I'm nominating you for the annual "loop diplomacy award",which will be awarded at the next salmon dinner.

savyboy

100 hours is time-out for Cup hubs (not axles) and there is no reason to think otherwise for tracked GT3's.

Here is some info guys, there are several tell-tales that the CL nut has lost torque or been incorrectly torqued. When this happens it allows the braking and acceleration force of the wheel to be transmitted into the hub (Pete S. I presume you mean "hub" when you say "stub axle") rather than the wheel flange to brake disk hat flange as is meant to happen. The drive pins (red nubbies) are proof positive if this has ever happened in the life of that hub.

Also, if the nut got really loose, the CL nut will show damage in the form of areas of metal transfer on the conical seating face. Also there will be a damaged area in the circumference of the hub where the inboard end of the wheel is. In my experience, the damage you see below is unambiguous and indisputable that it is only caused by a CL nut that had in some point in its life lost torque. If this evidence is there, the hub must be replaced.

The red nubbies in pic below are left to right: 1. Wheel very loose and/or for a long time and/or many times. 2. Wheel got somewhat loose sometime. 3. As expected in normal use with perhaps a few scratches from wheel install/removal.

The Porsche inspection bulletin (see attached) is clear that if the CL nut has ever been lose, the hub is to be replaced.

The fact is many shops and trackside support people do not understand proper CL removal/install procedure and consequently the CL nut gets loose and at that point the pin of the hub breakage grenade is pulled and there is no way to know how long the fuse is. Is your car shows the signs of a loose CL, you must replace the affected hub.

***The photos below are the work and property of Pete Hitesman and may not be reproduced or posted in any other forum without my express permission***

10 GT3

I am not going to engage the whole centerlock plus/minus issue, just rather stay in the spirit of the original post on safety. I have a friend who made a very poor driver judgement mistake in his 996 GT3 that resulted in flipping 6-7 times end over end at about 100 mph. It was just a member day and he had an instructor with him in his passenger seat. His car has a Porsche Techequipe rollbar, Euro GT3 seats, I believe the oem spec Schroth harnesses and both were wearing SA spec helmets. Both driver and passenger walked out of the wreck without a scratch. It wasn't until later in the day when they were driving back to town when they were both getting headaches from the concussions they received which ended up being their only injuries. This just shows that even in a street car, there is a huge benefit to having adequate safety equipment. Whether you have 5-lug or centerlock hubs, street or race car; it does not change the need for safety equipment.

CRex

Pete, your info is golden as usual. The bulletin includes extensive pictures which are kind of difficult to make out in low-res B&W but I get the drift. Any chance we can get a better, colored version?

brim

Good post and reminder. It's like anything in life that you expect to keep you alive in a dangerous environment, you need to be mythodical and thorough. There is no such thing as being too thorough when you're life and the lives or your fellow D/E buddies are on the line.

Would you ignore a operating procedure or potential issue with a parachute before you jumped out of a plane expecting it to deploy before you hit the ground. CL (and 5 bolt) is no different - among about 100 other things that you need to be aware of on your car.