When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Here's my theory on this:
front springs too soft
needs thicker or heavier bump stop
soft cast top plate is punched out when shock bottoms out
really not acceptable.
Wonder if the 991 GT3 has stiffer front springs than GT4?
This thread began with a GT3 shock tower failure but due to a crash-type impact with a curb.
I'll add to your theory and suppose that multiple bottoming impacts of the shock can cause stress fractures and fatigue cracks and then a dip in the road like Joe hit finishes it off.
EDIT: Last weekend I was driving my GT4 on some fun backroads, but there was a 2 or 3 mile section that was pretty rough with lots of patching and a few whoop-de-doos. I felt my rear shocks bottom at least twice, but don't recall hearing the fronts bottom. Car had 3/4 tank of gas and about 400 lbs of passengers and cargo on board.
I'll add to your theory and suppose that multiple bottoming impacts of the shock can cause stress fractures and fatigue cracks and then a dip in the road like Joe hit finishes it off.
How hard are people hitting holes or objects to do this?....obviously hit an decent sized object or really big hole at high speed and something is going got to break, hence trying to understand it more.
If I hit something really hard, as a driver I know something simply has to give or likely break...so the engineer in me wonders if this failure at the strut top seems a fairly safe way vs wheels disintegrating at high speed upon impact, or ripping suspension or steering arms off in ways that leave the car uncontrollable post impact and lead to potential massive secondary incidents. Ie...maybe these failures, examined in the context of the scale of the hit, are remarkable in that the cars could even be driven.....there's a contrarian glass half full thought for the day.
I wish I could drink from that half full glass, but this failure mode is unacceptable to me. I could accept the uni-body taking a permanent tweak from a heavy rolling wheel impact (like the GT3 that started this thread), and the tweak could be un-done with a session on a frame straightening rack. Taken at face value by Joe's description of the event, his car has been used like it was intended to be used, and the failure occurred. What looks like a very expensive failure based on the earlier post where it cost $30k. Unacceptable. The shock tower should be stamped steel or aluminum, not a cast part.
Just wondering, is anyone aware of a shock tower failure on a non-GT car that occurred when there was no severe crash-like impact?
To the engineers and metallurgists out there, do you think a strut tower cross member would add any support? Pictured is one offer by Schnel for a 981..
I'll second that the strut tower shouldn't be a casting, poor choice of material on Porsche's part.
Other parts should be the first to fail, never the body structure.
I hit a pothole at highway speed in my Audi, only damage was that the front forged wheel cracked, causing a slow leak.
To the engineers and metallurgists out there, do you think a strut tower cross member would add any support? Pictured is one offer by Schnel for a 981..
A strut brace won't do a thing to stop this mode of failure.
To the engineers and metallurgists out there, do you think a strut tower cross member would add any support? Pictured is one offer by Schnel for a 981..
No this won't help at all. You need to hold the top of the strut tower down . Look at the club sport body Porsche has plates on the top of towers that are attached to the body to prevent from the top getting blown off. Carl
I agree it could be that over time, with multiple 'hits' some small fractures occurred, which lead to the final BIG failure. As noted along the way in the tread Cast Aluminum is on the brittle side. While a good choice for weight reduction it is not the best material for higher loads. If these possible stress fractures occur first in the wheel side they might be hard to find without a disassemble and a full on NDT of the casting. One should have a very close look at the torn edges on the failed casting. If they are all 'fresh' they would all be the same color, if there was some smaller older ones, they might just show some aging, so a different color in the torn material. With a aviation background I have done some reading on post crash analysis, looking at various structural failures. The fresh verses old stress fractures can be telling.
Last edited by sctanton52; 11-19-2016 at 07:11 PM.
Reason: Spelling
It was at regular freeway speed, 55-65. I am anxious to hear if there is any other damage underneath that will give more info about whether I actually hit anything.
And I only autocross, and drive to/from events. Never a daily driver and never been on a track with it. I hope they can read the chip data and see the car's never been at track speeds etc.
This is what a clubsport looks like.
I'm aware of a similar failure on a 991gt3 in the rear.
The gt3 and gt4 are similar front ends. Spring rates different but unsure of other differences.
I just went out to the garage and had a look at the Boxster. You get a decent view of the underside to the strut casting. If the car was on stands and the front wheels removed I would call the view very good. What would be interesting, but very hard to do, would be to have a look at the various failed strut castings to see if there is a 'common weak point'. Again getting back to aviation, that is a technique used to locate design/fabrication flaws in all certified aircraft. But aviation is much, more controlled and has systems in place for tracking multiple failures. Joe, if you can, take a nice bright flash light and have a close look at all the torn edges on your failed casting.
The post by Spyerx, with the photos, I think is telling. Those added black steel (I am guessing steel) plates look like they are designed to transfer some of the loads to elsewhere on the frame, taking some of the load off the castings.
Just looked at my car and the plates in their present configuration won't work. because there is extra bracing running from the firewall to the tower that the plates bolt to. I do think someone could design a simular plate that would work on a stock car. Carl
11-19-2016, 05:50 PM
