[Aces&Eights]

On more than one occassion during my studies on wingless sprints I've seen horrific crashes resulting from the RR axle shearing off in the turns w/o contact or seemingly rough conditions. Why does this happen? Is it a birdcage issue and possibly the bearing froze up and cut thru the axle? Or is it a lack of inspection? What is the rule of thumb on RR axle life span? 2 of the worst I've seen were both at PAS for the 360 Oval Nationals during qualifying. Like Markus Niemelä's crash... I talked with someone familiar with the crew that said it was all new equipment.

[Mattmac05]

That's a good question, that is hard to answer. It could be a combination of things, the car may not make contact just before the wreck, but something could have happened multiple nights ago that could have damaged the axle and it just finally gave out. I would say lightweight axles, excessive re-straightening, and not noticing cracks would be the main cause. And many times all three. Personally I don't believe lightweight axles provide much advantage. Not sure how much weight is saved, but I couldn't believe it is much. There is always the argument that lw axles have less rotating weight, but the radius of which that weight is rotating at is less than an inch so that advantage is slim to none. I believe the risk-reward of LW axles is not worth it, especially when you see how hard sprints and midgets are run.

[LEADERS EDGE]

Not all axles are built the same and there are manufactures recommendations for the amount of laps that they should be run. Many don't follow those guidelines.

Other times a birdcage bearing may have an issue and it cuts the axle causing it to break.

Sometimes it is damage from contact.

[jdull99]

How often did the steel ones break "back in the day"? (like 70s & 80s?). If the answer is "not too often" then they should be mandatory. & if the thought against that is they didn't have the load put on them "back them"; then restrict the motors SOME & have smaller RR tires...

[mike mcghee]

Preventive maintenance can reduce the chances of this. Removing,cleaning and servicing birdcages nightly only takes a few minutes. Having rearends checked and replacing bearings and seals periodically is fairly inexpensive considering the alternative. Same with front hubs and spindles, a front bearing freezing up can cause big issues.

[Aces&Eights]

Thankyou, I appreciate everything I can learn as I work towards my move into sprints. That poor guy I mentioned has permanent brain damage.

[Tim]

Folks,

Any root cause analysis of this problem must start with the location of the break. These axles have several shoulders machined onto them to allow for bearing locations, etc. As anyone familiar with stress concentrations can tell us, square corners at these shoulder locations are stress risers which invite crack development and further propagation (growth). I would assume the axle manufacturers have a designed radius at these locations but maybe some aren't using a generous-enough radius as to minimize the concentrated stress. Another possibility is that the axle radius is proper but the steel spacer used between the bearing and shoulder may not have a radius in the interface location that is more generous than the axle. This would result in a cutting action into the softest member of the interface, the axle, which would further result in crack initiation. Compounding this, the cantilever forces acting on the axle at the birdcage interfaces along with any heating/cooling cycle embrittlement just add to the possibility of a crack. And, just to help things along here, we reduce the axle wall thickness so that the critical flaw size necessary for crack initiation becomes smaller. Any additional high forces resulting from contact pretty much guarantee issues.

Inspection and proper birdcage maintenance along with insuring that stress riser points are minimized are a few of the things I do in an effort to maximize axle integrity. I am also not a fan of the ultralight axles for the reasons mentioned above but I understand the physics of keeping rotating weight as low as possible. I just have not been convinced that the reward is worth the risk.

Tim Simmons

[Gene Franckowiak]

I would say the amount of races on the axle is one cause as things do not last forever and the other is a lot of people striaghen bent axles which also leads to failure.

[TQ29m]

It doesn't take much, catch a rock between the axle and a chassis tube, even a tommy will get the axle into a chassis rail, and put a ring on it, and that's all it takes I'd say any axle with the anidization removal ring on it, has little time left, the rear axle goes thru a lot of gyrations, torque, bending, flexing, twisting, probably more than any piece on the car, so it's a sure hi maint item. Bob

[LEADERS EDGE]

Over the years of watching dad take car of race cars and servicing parts for others througj the 70s and 80s and listening to him talk..... There were several cars that broke the old tapered steel axles and the splined ones.