BioBanker

GoKart Mozart

I agree, to prevent this from happening we need to avoid bottoming the suspension. What about helper springs? I am not an expert on what their purpose is, but based on what I see, it looks to me like they are for just that. They looks stiffer to me and might only come in to effect when the suspension travel is used up.

4carl

I still haven't seen what bump-stop is supposedly inside the shock. All the normal shocks have an external bump-stop at the top. Thats one reason why you dont see the failure on the reg suspension unless you really run over something like a curb . Ive always wondered if they eliminated the bump-stop it to get the car lowered and still have enough suspension travel?? carl

911-140.6

Agree- even a thin high density rubber bump stop would absorb a decent amount go load shock. Hmm...might pull off my front suspension this Spring to have a look at what might/can get fitted there.

ajw45

The helper springs are fully compressed when the suspension is loaded and they are primarily to keep the main springs seated when the suspensions gets unloaded. Running stiff suspensions with short springs and no helper is fine, you just get the occasional cartoon spring noise when they pop into place. That said, I think I read somewhere that Porsche found on the RS cars the helper spring does round the the initial spring response curve so maybe during transitions and in that phase from static to dynamic load they add a touch of measurable compliance.

I'm liking the idea of stiffer springs more and more.....

GoKart Mozart

Thanks for the clarification. Sounds like they do something completely different.

jkfuel

Wow, I was just made aware of this after a local owner had this issue. Apparently PCNA is "aware" of the issue and that there are service bulletins illustrating how to fix it just like others have alluded to.

911F1

Adding a clip on style bump stop might help out

Petevb

The issue with putting anything flexible/ elastic between the shock top and chassis is that it would always be loaded. If it were polyethylene you'd tighten the shock down and it would "creep" under load (like nearly every plastic does) until the the stress was relieved and the bolts were loose. If you put something elastic there it would threaten to deflect when you didn't want it to. Thus what you really want for that location is something like foamed aluminum with a known crush strength- rigid until it takes a big hit, then it deforms to absorb impact.

Adding a bump-stop (essentially an extra spring) to the suspension is a good thought however it will threaten to dramatically change the handling. It will need to come into play early due to the short suspension travel, and when it does it will work just like increasing the spring rate or tightening the swaybar- the handling balance will change in significant ways, and you'll likely only find out how mid-corner near the limit right when you hit a bump. So while it's an easy fix on paper it's much more complex than it would first appear.

4carl

interesting idea? you could cut it in half if its to thick to maybe 1/4"? carl

GoKart Mozart

Disclaimer, I am not an expert on suspensions, so correct me if I am wring, but I don't think a bump stop would come in to affect under "regular handling" situations. Even though the GT4 suspension doesn't have that much travel, does it really get loaded up to the last inch unless you hit a massive bump? Just look at my Avatar for example. Inside wheel of the ground, so the outside suspension is about as loaded as you could expect, but it appears far from bottomed out. Don't forget we have PASM (active suspension) which should help in most handling situations to stiffen up the suspension, but a bump is different.

I could see this being an easy fix. Maybe not 100%, but might help a little

speedy974

Do you guys think that the strut tower brace from the GT3 Cup / GT4 Clubsport would help with this?

A432

CardiffDweller

There was an update yesterday on youtube's "vehicle villains" channel for that yellow GT4 that had the strut tower fail. The link is easy to find. It was hard to understand the Scottish mechanic through his thick burr but I think he was saying that the first crack started with one of the vertical bolts on the right side of the tower if facing the windshield. The owner said Porsche told him it wasn't covered due to some sort of external forces verbiage. Interestingly, his repair quote was on the order of 5 or 6k pounds. They discussed removing the fender for the repair, plus some of the panels, and pointed out the glue that Porsche uses to secure the strut tower. None of them mentioned using a jig for the frame straightening so who knows. I had a little laugh when the owner wiped off a big deposit from a flying bird off the fender, smeared it onto the tire, then put his hand right into his pocket, then continued to drink his coffee with that hand and the lid off the cup.

ajw45

Thanks for posting! I read through the comments, seems like 991.2 GT3s are also failing the same way...