After some homework, I found a shop in "central" Florida that could align my car including measuring/setting rear caster.
Stingray Chevrolet in Plant City, Florida confirmed that they had the tools to do so and a week or so before Roebling I took the car there. Their shop foreman (Robert Hoover) did the work and showed me the Kent Moore tools he used to measure and adjust rear caster.
This is the pre-track alignment and Robert confirmed that (since their Hunter rack doesn't measure it) the rear caster was zeroed out.
What we're looking at here is the "actual"...

Target was -2.0* camber and .05* toe in with 7* caster front and 0* rear. This wasn't bad.
Minimum corner speeds were up at several turns at Roebling, including T3, T5 and T9. First session out the car ran several :18's. Second session it "only" ran a best of a :19.01 and several :19's with my father in the car and the AC running (lol). However, after that it pushed to :20-:21's in the afternoon with temps in the mid-90's.
I attributed it to track surface temps of 140*-145* and greasy conditions. While that may have contributed, so did this...

(I mark the eccentrics before on-track).
We're looking at "before" here...

Front toe went from ~.05 toe in to ~.50 toe out. Rear is similar. Camber significantly changed. And left rear caster (not shown on print out) went to "2 degrees".
I put the car on my lift today after returning home and made sure the CA bolts were tight after marking the eccentrics. Will be watching this at the track in a few weeks.
S.

 

This will be a huge PITA, and surprising that it's not a known condition since they have been using this eccentric bolt setup for a while now. Why now are they slipping? Is it the adjustable rear caster?

My alignment cost me over $500 labor at a local race shop because the dealer didn't have the tool to measure caster. I don't want to have to keep resetting this after every event.

 

Isn't this the same prob it had at VIR against the Nismo?

 

My 2009 CTS- V had same problem after alignment. Eccentric moved enough for steering wheel to go off-center.
Fix was to over torque the bolts by a huge amount in order to keep eccentric from moving.

 

What's the torque spec and did they use a torque wrench?

 

As I continually point out to those that don't know: the torque spec for those eccentrics is MFT. No torque wrench required. If your alignment person tightens them down to the service manual specs, they will move on track. It's been that way since at least the C5.

 

Yep. And it's my fault for thinking that the dealer would torque the crap out of them. When the car was on the lift and I marked the eccentrics, I should have put a breaker bar on them as we did when my friend aligned the car at his store.
S.

 

How is the back of the nut/captive washer combo surfaced? It seems it needs a higher coefficient of friction to reduce movement of the concentric at a reasonable level of bolt/nut compression.

Alternatively hire the guy who installs the oil filter on the Duramax diesel engines at the assembly plant in Ohio to torque them down Both of my pickups required an incredible amount of force to remove the factory filter.

 

I know how tight those are on from the factory; it's still not tight enough.

 

I think I would be a little careful about overtorquing those bolts given that the cradle is magnesium. When I was running Hoosiers which gave a huge increase in load over the stock tire I usually found that the bolts would loosen because of insufficient torque, but even if they were torqued to specs, you couldn't just forget them. I think part of your track prep should be to recheck the torque on those parts, as well as other bolts that hold important things on the car.

 

I do check them between events. The alignment was done a week or so prior to Roebling. I found everything loosened up after that and while prepping the car for the next event in two weeks. The alignment was set and marked prior to my first event with the car at Daytona in April. The eccentrics were marked and I checked it again prior to Sebring and then Roebling (in May), including throwing a bar on them to make sure they remained tight even though no movement was seen.
So yeah, checking these regularly is good advice.
S.

 

In the Dark on this subject......

Hope this thread goes on to explain things in depth, thoroughly.

Links to reference material on this appreciated....

 

Hrmm i should go get mine double checked since ive tracked it a few times. The shop i go to is known for working on track setups and race cars and the owner himself does time attack in his C5. So hopefully it should be good.

 

I'm not sure what you're after. The learning from this is "School of Hard Knocks" meaning years of experience with Corvette eccentric bolts. It's one of the reasons why (on previous gen cars) camber kits have been developed: to remove the %#!@'ing eccentric bolts and replace them with blocks that can't move. No such kit has been developed for the C7 yet that I'm aware of.

The service manual has a listed torque value for those eccentrics. That value is too low and has always been that way. If it's set to that value (likely what happened in Snorman's case) and the car is shod with sticky tires, the eccentrics will very likely move and re-adjust themselves, knocking the alignment all out of whack.

If you want a good education on how these bolts work, ask your alignment guy if you can watch him adjust your camber when he does it. That should clear things up, if there's any confusion.

 

Getting close

 

Nice mod!!!

 

Does that picture mean that Van Steel is making the plates for the C7 now?

Bill

 

These are for a C6 but they are very close and might be fine. There is less than 0.5mm clearance but I think there should be a bit less. I'm working with Van Steel to get them done.