trkshoe

I finally got around to removing a strut (yeah... I know) and it does in fact have a bump stop.
I think stiffer sprigs are very necessary... and don't freakin lower the car.

gbeaty

Great info, thanks. Does the front suffer from a lack of bump travel? This is, does the shock bottom out a long time before the tire or wheel would hit anything? On race cars with steel strut mounts, I usually remove the string and modify or re-position the upper mount so the strut bottoms just before the tire starts to dig into anything.

trkshoe

I imagine any mfg would do the same... once I have the spring off, I'll compress to see where the strut bottoms (tops) out.
I was spit-wadding ides, and a top hat with an extra inch or half of travel would be helpful as well, along with a longer bump stop.

G-forceGT4

^^ Thanks for doing that & sharing the info. I'd like to get some idea as to how much the Swift springs alter ride quality. I could see a real advantage of switching them for track purposes, & if the ride isn't bad with them to use for street as well for added protection.

switchface

Regardless of how pervasive this failure might be, wouldn't stiffer springs only exacerbate the issue? By nature, wouldn't a progressive spring help alleviate the initial transferring jolt?

chapmans

I think the goal is that the stiffer spring won't bottom out as easily and will avoid the big shocks to the tower.

trkshoe

Exactly... that's the 'jolt' we need to avoid, so the stiffer springs further dissuade the shock bottoming out and transferring the 'impact' force to the hat.
The bump stop does the same, but in a less progressive space (distance).

911F1

Is this the actual cause? The shock bottoming out. Has anyone identified this?

chapmans

Noone has actually real time documented a failure so the exact mode of failure isn't really known.
I think a reasonable assumption is that big impacts bottoms out the shock, from there that force travels directly through the top mount into the aluminum strut tower.

The GT strut mounts don't have the rubber isolation that base cars do and thus lack additional absorption that mitigates this. Base cars have both longer bump stops (I assume?) and rubber isolated top mounts to absorb and spread out the impact jolt which seems to keep everything under that critical force value that causes failure. This is in addition to the extra ride height on base cars that gives the suspension more time and space to decelerate and absorb impacts. That's my guess as to why you don't see it on anything but GT cars.

The lingering question that I have is, is this a cumulative fatigue problem or a catastrophic failure from a single impact? Or both?
I think some people said theirs failed on smaller impacts that likely didn't bottom out the suspension so that would lend credibility to the fatigue idea.

If the bottoming out hypothesis is right then stiffer springs should help. If it's a issue of fatigue failure due to a series of smaller impacts then they probably won't.

I think the best thing you can do is run some lightweight 18s to add some impact absorption back in until some vendor comes out with a good reinforcement solution.

Michaelpickett

I have a deposit on a GT4 and after seeing this am thinking of cancelling purchase for safety reasons related to this failure Porsche does not seem to stand by this and repair under warranty any thoughts?

HelpMeHelpU

Immediate thought is that your concern is overrated and an incident is highly unlikely. GT4s have driven hundreds of thousands, if not millions, of track miles and the number of incidents is very small as well as being unconfirmed in many cases if there was damage prior to entering the track. YMMV.

Yargk

It's an issue, but it's still a minority of cars. Not sure I'd base a decision on it, but the ones who have had the failure might beg to differ

mcomet

You should absolutely cancel your deposit and then send me the allocation spot... on second thought I'll keep my 981 GT4....

Michaelpickett

I may not have been clear, my deposit is on a 981 GT 4 with 12,000 miles. Very concerned about the shock tower failure and assume it is s stress related issue so the older the car the greater the chance of failure. I understand that one failure was on the freeway with no track use ever.

d00d

I'm assuming most or all fail completely without an intermediate hard to see failure, but use Zyglow and a black light to confirm there's no damage.