PLNewman

There was a discussion here recently about lower control arms failing. Mine were about 5 years old and were due for inspection when the left-front gave up the ghost during the sprint race at Road America. It could have ended much worse (as you can see from the video). Five seconds later and I would have been in the infamous high-speed "kink" and probably doing wall-to-wall ping pongs. Replaced all four PSS9s, all the control arms, a L/F upright and bearing assembly, and a new front fender and liner. Walked away with a bill for $7K. Could have been MUCH worse.

mmuller

I have personally had them break at the inner side, but it’s completly expected it could break at the outer like your has. The problem with the 996 GT3 arms are that they are cast. 997 arms are forged and would be better for reliabilities sake, but not legal.

I urge everybody to inspect these items regularly. We are all driving these cars pretty quick these days, using all the track as much as possible and regularly running over the turtles. All bad stuff for these cast parts. Also, when the car has an impact in a corner, it would be prudent to swap these out, even if they look ok.

ace37

Anyone know a cheap version of flourescent penetrant inspection? (We do it in aerospace but costs are on another level.) Seems like a glow green fluid and a blacklight would make an easy inspection technique that would help us detect smaller cracks. Maybe checking the suspension parts would be a prudent part of winter maintenance.

Anyone know the material they use for these parts, meaning the exact alloy? If I get lucky and can track down data I'll tell you guys the critical crack size (where a full load impact would split it) for a few assumed laod levels. I'd need help knowing what loads to use but we could figure that out.

PLNewman

Any idea why PCA considers the stronger 997 arms illegal? Is there an advantage to be gained? Does it outweigh the inherent risk?

CTS

Thanks for posting this. Sharing things like this will eventually save someone some real trouble.

Questions:

Are you running the brake disc heat shields on this car or have you removed them?

Do you know the approximate mileage on the arm that failed? Was it new when it was installed?

Any significant impact history for this arm? I consider an impact strong enough to damage the wheel significant.

Are you in the habit of placing jack stands under the control arms when working under the car?

Are you still in possession of the failed arm?


Thanks,

Chris Cervelli
Cervelli Technical Service

jdistefa

Mike - glad you posted this.

As we discussed at Road America, the prudent thing to do is replace the lower control arms at 50 hrs.

ace37

I'm not sure there's a reason besides it not being the specified part number. I've read here that it's stronger as it's forged, and it's also lighter for the same reason. I haven't seen a figure for the weight. While I expect the real impact of the change alone to be negligible there may be a perception of a competitive advantage going to the guys that install the forged parts. That's probably the biggest hurdle to a rules change. If the cost to swap is sufficiently modest it may be something to suggest as a rules change.

I saw there was a fire in the cabin in one region and the Cayman metal engine cover was recommended as a safety precaution. After posting about that the response was reluctant due to lower weight of that metal cover, somewhat high cost, and perceptions of competitive advantage differences if it isn't a uniform part of the spec formula. If it ain't (very) broke...

jdistefa

The forged 7-cup LCAs are twice the money. Teams often replace them at 30-40 hrs or magnaflux or xray.

Cory M

Grainger sells a nice penetrant kit. I've used it in the field. It isn't FPI but uses a red penetrant and white developer, so no need for blacklight etc. It works well and isn't much $$.

mmuller

You can achieve the same thing with the Boxster cover. You just have to gut all of the sound insulation off it, which does make it lighter

txhokie4life

Sorry it broke on you but glad you are ok.

since I have the same build, I’ll be keeping an eye on things.

mike

txhokie4life

Send pix to Walt with replacement details and inquire about a rule change.

like you said, had this happened some where else or say at the beginning of a race, could have been far worse and might have collected other cars.

mike

hf1

+1
OP should send a rule change proposal with pics attached. The performance gain would be negligible, if any, and far outweighed by the safety gain. This one is a no brainer.

ace37

If this is the case I don't thing a rule change would be of any great help. The same parts would last longer on the Boxster, but it's hard to argue it would be dramatically longer.

The biggest thing that would help I think is if they'd start to be penetrant inspected annually as a part of winter maintenance. If anything is concerning, swap the parts.


This probably sounds a bit strange, but since I come from the aircraft world it's intuitive to me... can we get a set of required annual inspections specific to each platform? We could simply do a due-diligence level of inspection for any unique and dangerous failure modes that have been discovered over the years. No inspection items if nothing is known or observed. Tie it to the annual race inspection...

Matt Romanowski

I haven't used this brand, but check out and then look at the frequently bought together link. About $25 for everything. Magna Flux dye penetrant kit is about $100.