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Are you saying that the rear wheel bearings were both replaced in March, and then this failure happened right afterward, or did you drive the car (and fail another rear bearing) since March? If it's the latter, and you had the axle fail during recent rear bearing replacement, that's interesting. Did you really chew through a new rear bearing in a matter of 5 months? It sounding to me as if something wasn't right about the bearing replacement that took place in March. And that may help explain the more recent bearing and axle failure. Could it be that there was not adequate torque on the axle nut at that time? Or that the worn-out bearing back in March caused fatigue damage to the axle that just now became evident?
Rob
Rob, happy to answer any and all questions for you.
I replaced all of the wheel bearings on my car as a preventative measure this past off season. They have around 1500 miles of street use on them and approx 7 days of track use this season.
I do most all of my own mechanical work so that I'm the only one to point the finger at . However I don't have the necessary tools to press the bearings. I had the local Porsche dealer do this for me and I watched the process and saw no issues with it.
I put a torque wrench on everything I can, including the axle nuts, before every track weekend that I attend.
As sated the other 3 bearings on the car are quiet and tight. I'm having a tough time thinking this is anything other than possibly just a bad wheel bearing but would love to hear thoughts otherwise.
What's more difficult for me to really guess on is if the axle is actually related to the bearing failure or just age / use / etc.
** I'll dig out the SLR this weekend and get some better pictures for you guys. Also going to tear apart the CV joints to see how they look**
I don't want this to get too far way from the original topic, but here's a picture of the bearing that literally fell apart when I pulled the upright off of the car.
and the damage to the hub where it was riding inside of the bearing.
Andy, what I find interesting when looking at your picture and mine is that the position of the nut seems to be different, unless it's an optical illusion due to the perspective of the pic.
Your nut seems to be butted right against the splines, whereas mine still has a way to go.
Maybe it's just because of the way it broke, while torquing, but weird, no?
Andy, what I find interesting when looking at your picture and mine is that the position of the nut seems to be different, unless it's an optical illusion due to the perspective of the pic.
Your nut seems to be butted right against the splines, whereas mine still has a way to go.
Maybe it's just because of the way it broke, while torquing, but weird, no?
When it broke I put the impact on it and ran the nut down further to help pull it through the splines in the hub to make it easier to remove. That's not where the nut was sitting when it broke.
Broke out the good camera last night and forgot how difficult it is to really get great detailed shots from a DSLR in low light when you are out of practice, trying to hold a heavy axle in one hand to maximize light and take pictures with the other hand.
Here are a couple of shots that actually turned out, I can take more if you would like over the weekend and do a "better" job next time :-)
Stub / broken off portion
you can see where the teeth are "polished" guessing this is from everything moving around in the bearing
Standing starts and hardcore hitting the curbs wear out your axles much faster and i am sure that heating up and cooling off steadily also plays another factor.
Also heard anecdotal recommendation to reduce the center bolt torque an wheel nut to 270 ftlb's with no ill effects????
That's what my shop also recommends. 996 Cup centre lock nut is torqued to 270lbft (approx 360Nm). Been running a car like this for over 25h now and the nuts never moved even the slightest bit.
That's what my shop also recommends. 996 Cup centre lock nut is torqued to 270lbft (approx 360Nm). Been running a car like this for over 25h now and the nuts never moved even the slightest bit.
I'd like to hear from race shops that prepare, support, and/or race 996 cups on this suggestion to reduce center lock nut torque.
I currently work with a team that runs a bunch of 996 and 997.1 Cup cars in the US. We've been running this type of car for 10 years. I also worked as a crew chief for a Grand Am team for 5 years campaining multiple GT3 Cup cars. All axle nuts and wheel nuts are torqued to 350 ft lbs as stated in the factory manual. We've seen a couple shaft failures at the outer CV but this area is not affected by nut torque values.
I will reiterate that I called a PMNA Engineer that I know six months ago to discuss the "reduced torque" and he did not recommend it on 996 and 997.1 cars.
I have also heard that dropping below the 350lb-ft is not a good idea - perhaps one of the MEs can chime in here.
I torque mine to 350 lb-ft and also lightly grease them (pretty sure the manual indicates this). My tires have been on & off more times than I can count, and usage is pretty high as well...
I suspect that tires (slicks vs r compounds) play a role here, as does driving style (miss vs plow over turtles) as does how hard you drive
They raced quite a lot of 996 back when it was still a recent model. Good thing for me is they have spares which they don't use anymore since everyone is running 997/991 for quite a while now.
My tires have been on & off more times than I can count, and usage is pretty high as well...
As on any race car I guess. The car is transported on 10 year old tires. I never leave the ones that are still good to use on the car before or after an event. Always install them in the morning and remove them after the last session before putting the car back on the trailer.
09-24-2015, 09:21 AM
. However I don't have the necessary tools to press the bearings. I had the local Porsche dealer do this for me and I watched the process and saw no issues with it.
