Just got a call from the dealership... apparently the final diagnosis is that my LSD has gone bad and I need a new diff.

 

yikes, thats gonna be expensive. might as well go after market. UPGRADE TIME!

 

Yeah no kidding... I've got a couple other small things I'm going to try as a last ditch effort (swapping tires, changing swaybar), and if that doesn't fix it I'll be ordering a Puddy stage 1.5 diff.

FML

I'm still trying to figure out how I managed to break a diff. I've never launched the car and only tracked it once (rather timidly I might add). I drive the car hard on the road, but I never beat on the drivetrain.

 

Try Amsoil 75w140

 

Just to give closure to this issue. The actual problem turned out to be a failed rear shock absorber (Koni). Under hard cornering, that one shock basically quit working - basically leaving nothing but spring action at that one corner. This caused the wheel to judder heavily when you got on the throttle.

I'm now back on the OEM suspension and the car is cornering like a champ. I just wish the real problem were discovered before I spent $1000 on a diff. Oh well.

 

Your only fault was listening to the dealership. How long did you drive on the shock before it failed?

 

Which is hilarious because this problem stumped EVERYBODY I talked to - including the dealership. Not one single person I asked about the problem (including the forums) suggested that it might be the shock absorber.

As for the failed component, I have reason to believe that it very slowly went bad over the course of about 2 years. The vibration started off as being very subtle, then got worse and worse as the damper performance degraded.

 

Well usually when a damper goes bad you can tell because then there's nothing controlling spring movement. It's kind of hard to infer a bad shock as a cause of vibration. But...you live and you learn, I'm in the same boat don't feel so bad, the POS Taiwanese coilovers that were on the car when I bought it are shot on my end. I'm going to cannibalize any part I can reuse and stick it on some Koni yellows. I didn't even know they were shot car drove fine, no unusual vibrations, but it was the fronts for me.