DJN

CRex,

Thank you for starting this thread and putting your facts, observations and thoughts together for everyone. Excellent!

After reading this through I began thinking about the all of the forces acting of the rearend of a GT3/RS - acceleration, braking, and lateral forces - specifically in the hub, axle and bearing area of the car. In order to to loosen a properly torqued CL rear wheel (say, the right rear wheel as in your case) and not the other (the left rear wheel), there must be one of the following conditions to allow such an occurence:

A) Rear Wheels were not torqued equally - but we can easily rule this out based on the amount of experience you have changing and torquing CL wheels

B) Internal friction or torquing force of the CL mechansim unequal due to the phyical condition of the mechanism - previous wear possible as you suggest, or due to possibly differring amounts of grease inside the CL mechanism. NOTE: Before last year's new CL R&R procedure (the official CL Supplement for owners), I was using much less grease than suggested on my CLs (when I had them! ) - this resulted in extremely high breakaway (loosening) torques after a weekend of track events, on the order of 600 ftlbs or more. This new amount of grease, while specified, will be applied differently by everyone, and could be the cause of some issues.

C) Additional forces acting of one of the wheels - more lateral force the rightside on a regularly visited counter-clockwise race track........or (now this is my bomshell) could this be caused by additional forces on the right rear by a worn out factory LSD? This would cause a greater value of positive and negative forces (an oscillating effect) acting on the right side CL mechanism to slowly but surely work the system loose over a realively short amount of time.


So a couple of questions:

1) CRex, do you still have the original LSD in your car. If not, when did you change it and what is your current mileage?
2) Is you hometrack clockwise or counter-clockwise?

Cheers!
Doug N.

NJ-GT

I have a suspicion on the Right Rear wheel coming loose.

It involves the more than 1,000 ft-lbs of torque generated during heavy braking + ABS + PSM + locking splines unlocking or unable to handle the torque. Think impact wrench, and that's what ABS is doing to the RR wheel.

This would only apply to the right side, because a wheel trying to stop (hub, axle and CL nut are tied), would apply forces to loosen up the CL nut on a wheel/tire rotating forward.

senna

Interesting video on F1 wheels coming off. Not the same design, I know but...

http://www.youtube.com/watch?v=PeIqXgaoSNM&feature=youtube_gdata_player

kosmo

i was thinking the same thing.

The Greek

Rad,

Ironic you said this. I noticed a couple times that the right rear broke easier than rest of wheels. This only happened a handful of time, but still stood out as odd.

Might just be coincidence.

NorthVan

A simple CL to 5 bolt conversion will solve this issue.

I didn't consider a .2GT3 because of the CL wheels (didn't know about the conversion until after I bought mine).

stout

Have been wondering about the RR failures, thinking about the weight and forces involved. The observations you've laid out as well as NJ-GT's theory are pretty interesting. Quite a few interesting thoughts, actually.

Thanks for posting, CRex, and good on you for your thorough approach to safety! By sharing your diligence, you might just be saving more than your own hide...

pete

DJN

Hmmmmm, interesting........

kosmo

Sure. w/ more hp , bigger brakes, & LEDs, i do find the .2 more desireable.

Rob S

Here's an interesting discussion on a British car forum dealing with "knock off" wheels as they are known to the Brits. My first car, a TR6, had knock-off wire wheels that had left hand thread on the right side wheels, which were tightened by (the highly accurate technique of) several crisp blows with a lead mallet. Though we've come a long ways since then, physics hasn't changed at all, nor has the concern about wheels coming loose.

http://www.britishcarforum.com/bcfor...inner_directio

savyboy

I am loving that mental image of hot mechanical interaction but there would have to be evidence left if such a thing had occurred. But I've never seen that kind of evidence on the locking spline mechanism? Nor is there an explanation of what would cause the spring loaded splines to retract once fully engaged into the CL nut.

Nor do we have a full accounting of every wheel that has come off. There may well be an equal number of free-flying left side wheels if one had a full data set to examine.

The only way a CL nut could ever rotationally loosen while torqued down would be if splines were not fully engaged. Many other factors could result in a loss of torque.

In the picture below you can see witness marks on the inboard end of the mechanism, the result of it acting to hold a loose CL nut from loosening further.

kosmo

is reverse threading used in some racing applications like Nascar???

savyboy

Your homework, to be presented to the class (here) is to explain how the Porsche street CL system insulates wheel rotational forces from the shell of the CL nut.

Other than holding the wheel on, there is nothing similar in how the old knock-offs work and how the Porsche system works.

mdrums

Those boys use hubs that look like they belong on a big truck and use 5 lugs on steel wheels

malmasri

Isn't that what the 5 bolts do