peritus

The Canadian garage queen Turbo S, transformed to Ring-Tool has completed nearly 8000 km of exclusive Nurburgring Nordschleife laps last season and this season so far. Upon regular inspection, my garage noticed that the rear control arms on left and right side bent the bolts and pushed them into the rear sub-frame on both sides, requiring them to be replaced. They've asked local experts for a second opinion, and no one has seen this before, even though 911s are a dime a dozen here.

Yes, I thrash the ring over and over as I hunt the clean sub-8 lap. I get some good air off the jumps. I smash into the Carousel and sometimes take the odd curb.....,but I can't wrap my head around how this would be possible, no matter the punishment, even on the Nordschleife. For suspension, I have KW 2-way clubsport, and poly bushings. Control arms and sway are stock.

I've searched the depths of the interweb, and can't find any hint of this happening to any other 996... Anyone heard of such a thing?

Carlo_Carrera

Congratulations, you've done something that no one has ever done before?

peritus

LOL, not sure if congratulations are in order… new left and right sub frames will cost me a kidney!

Carlo_Carrera

True, but some would say that is a small price to pay for all the fun you have had lapping the Ring.

Bernard IV

You must really be thrashing that thing. Looks like a blast! I run the ring on my simulator. Someday.

sabba

Is that the eccentric bolt for the caster control arm digging into the subframe? Unfortunate but good thing this was caught before failure occurred..

What tires were you running?

peritus

Sabba, I was running Nankang AR1, as they are a super popular tire option over here, but get this, I had 3 rear passenger tire blowouts on the Nankangs. The first two instances, the tire blistered on the inside and I pulled over and then pop goes the weasel.

the last time it happened about 3 weeks ago at 257km/h! It exploded and took with it the inner wheel arch, the intake pipe!

switched to Cup2 but have yet to try them out since this issue arose.

Blowout at 257 km/h

moburki

These eccentrics are known to move under heavy use. It appears yours are still lined up with their respective marks, however. It is possible they moved, then moved back? There are ways to lock the eccentrics in place. My handling was noticeably whacky when mine moved (NA 996, but same set up).

powdrhound

The camber eccentrics can move or slip because they have a tendency to go out of "square" when doing the alignment if the chassis is not allowed to unload during certain steps of the camber alignment procedure. If the eccentric bolt ends up slightly out of square when you tighten it down, it will move/slip under load and you end up with the obvious drastic change in alignment or possibly with what the OP is seeing. I've done plenty of alignments on the 996 chassis and this is one thing to absolutely positively watch out for. This is why you have so many people complain of the eccentrics slipping but it's generally due to a sloppy alignment procedure. I do my own alignments and I will say that I've never ever had the eccentrics move and I track my car heavily on slicks where are see 1.5G of lateral cornering force on data with regularity.

moburki

I would be interested to find out which steps I might have overlooked. I didn't do the alignment, but was very much involved (not my equipment).
Any case, I'm still baffled that OP eccentric could have moved and returned to its original position.

peritus

Yes, it appears they moved enough to damage the subframe, and moved back. I'd go for the locking bolts and upgrade to an adjustable rear toe control arm, but the locking bolts are not TUV approved, and therefore illegal here for a road car! They're super strict.

powdrhound

Adding camber with the eccentric while the car is loaded on the rack is very easy. Reducing camber on the other hand can be problematic as it oftentimes causes the eccentric bolt to go out of "square" relative to the subframe when you force it. This creates the inevitable problem which everyone complains about with the eccentric then slipping under load.

Whenever I'm doing an alignment and have to reduce rear camber, I normally lift the car off of the alignment surface until the wheels are in the air (last pic below) and then reduce the camber past where I want it with the suspension unloaded. After lowering and loading the car back on the platform, I then add camber to my desired target. Obviously you may have to repeat this procedure several times because as you adjust camber it will naturally change your toe and vice versa. Doing it this way precludes any eccentric slippage issues and as I mentioned above, I've never had one slip when following this procedure. The alignments we do are based off of the wheel hubs and NOT the wheels themselves which precludes any errors as a result of wheel run out that invariably you will always have with traditional alignment rigs that clamp onto the wheel lip.

I will caveat this with the fact that in order to do it the way described above, you need to have an alignment rig that allows you to lift the car off the platform during the alignment process. Not many do however. The rig we use is pictured below and allows for precise race alignment of the whole car including setting corner balance as the car is resting on scales which have a ball bearing platform on top of them. Each platform has adjustable legs and is leveled relative to the others with a laser.

As far as control arms and all associated hardware, I've found OEM Porsche Motorsport parts superior to anything on the market.

2fcknfst

You're living my dream, good on ya!

powdrhound

I don't do this for a living but I do find it therapeutic in a way to wrench on these cars...

2fcknfst

I think I should retire and go and figure out how to do some mechanical Porsche Apprenticeship Program, if that even exists.

Then, spend 8k kms on the Ring. Good times.