Agreed

 

Agree. Mine slipped after my first alignment and 3 track days. Second alignment was done right by a different shop with 111lb ft +90 degrees and it hasn't moved. It is a ton of torque.

 

I had mine aligned with the torque + angle procedure and it slipped after two track days. That said I also use a lot of curbs at my home track. The shop that did the alignment has the fancy torque angle feature as well. 90 degrees after 111 ft/lbs was usually between 190 and 220 for total torque.

 

You might try these. I have not used them, but they seem to have been created for this problem:

https://amtmotorsport.com/products/a...WAHcT83C1WGiA1

 

That's just so much torque... M14 wheel stud spec is 140 and I do 125 given how often I have my wheels on/off.

 

Dialing in rear castor on these cars is a massive pain in the *** w/ the AMT kit. I ran them on my C5 racecar (no rear castor) and have them for my current C6 trackday car project (no rear castor). But when you have to loosen the UCA and shim it and then re-settle the rear suspension it's basically impossible to get it right.

I'm curious if everyone is actually marking their eccentrics and verifying 100% they're moving?

I tracked 3 of my C8s hard, but 2 had aftermarket alignments. The shop I used did 125 and marked them. All tracking done at VIR in instructor group and use all the curbs in the uphill esses.

I will up it on the next one, but 190-200+ seems nuts.

 

I marked mine with sharpie before I left the shop.

I've looked at the AMT kit, but since I usually only do 5-7 track events a year I'm not too worried yet. That'd be an off season part add if I did it. I have One Lap starting next week, then Grid Life Mid Ohio in June, then TTNats at Pitt Race in Sept. Probably a few other small events locally. If it slips again between those then I think the AMT would be worth it. The front is more likely to slip than the rear it appears.

 

Odd because rear has the 345s and all the weight.

 

It also doesn't turn or hit curbs as hard on track. About the only time I'd expect the rear to slip is if you go off track.

 

This is the proper way to stretch a bolt to its elastic limit without danger of over tightening.
a) You tighten to a particular TQ number on the wrench--this is a friction on the thread measurement.
b) you then turn it another number of degrees--this takes over to stretch a known amount over the TQ spec.

If threads were perfectly smooth with a known lubricant and a specified temperature, you could do it all with a TQ wrench.

Most race car motors {F1, WEC, NASCAR} use this on head bolts and a few others.
Yes, it is a PITB, on the other hand, so is a broken head stud after doing the first 13 nuts.

 

mine slips constantly. Pretty much after every track day I need to have it re-aligned. Sometimes mid day the steering wheel will turn 4-6 degrees and stay that way. Really annoying.

 

Well it's time to update this thread.

My OP was about a year ago. I had another alignment done to get more aggressive camber and they got everything spot on...the alignment report looked perfect. Car drove great. Then I did another HPDE a couple weeks later. After one single session, I came back into the paddock and noticed the steering wheel off to the left a few degrees again. Maddening.

I immediately took the car back to the dealer after the event and the shop foreman with whom I have a good relationship took this problem seriously. Flat out said "that should not be happening. period." I left it with them for a few days and then he called me with a discovery. First, the car measured terribly for alignment on all four corners. He noticed that when they initially unloaded an eccentric bolt, the whole suspension dropped like it was bound up. He did a new alignment, drove it, and noticed a popping sound from the rear end over an uneven part of the service drive. Put it back on the lift and went on a hunt for the source of the popping.

He discovered one of the rear eccentrics had a lip of extra metal on it, presumably a defect from casting. It wasn't allowing the eccentric to sit correctly. The hypothesis is they'd tighten it down but the forces on the suspension could cause it to move (from being incompletely seated) and then it would bind in the new position. The ground off the lip of metal and got the alignment spot on again. No more popping.

So far so good. The alignment changed (steering wheel suddenly off center) once when I quick-jacked up the car to change tires. That was enough to load and unload the suspension causing a shift. This tire change, no changes in the steering centering. So far so good. Hopefully the next HPDE shows it's all good to go.

 

Thanks for the update OP. I hope your alignment holds. Mine is going to the dealer tomorrow for it's re-alignment after it's first track day. I told them about this issue with C8's and they said they've never had this problem with any other C8's in town - I guess those cars don't go far beyond Cars and Coffee...

 

+1 these cant slip...Good luck finding a shop to do the alignment though, only one around here that would do it is a race shop. I ended up buying all the stuff to do my own alignements for what they wanted for one.

 

Well my issues persist.

After one of my alignments, the tech noticed there was a burr on one of the arms preventing an eccentric from seating completely. He fixed that. Got it all dialed in and spot on. Then I made an assertive turn out of a side street onto a main road and my steering wheel was suddenly 2 degrees off and I had a left pull again. Just lived with it for a while, did an HPDE and finally just today got it back to the dealer to check the alignment.

Complete mess again. Sheet attached showing what I came in with at the top and where they have me again as of this afternoon.
I'm either going to need the AMT kit or just call it over and done with my C8Z. Really had enough of this issue.

 

How do you know your steering wheel was 2 degrees off? Where did you get the 2 degrees number? How hard was the "left pull"? Typically if a pull is hard it's caused by either a tire problem or EXTREMELY far off caster settings...the caster numbers on your car were not off enough to cause a pull. Furthermore, caster causes a pull to the least positive or more negative number...so in your case if anything...it should have pulled to the RIGHT not the left....so it appears something else was causing your pull. I performed over 2,000 alignments as a technician when I was in my 20s...and I've seen many people confuse a steering wheel that's off center for a pull...not saying you're doing that but something is not adding up.

 

To avoid semantics of a pull or being 'off', I'll just describe it. Initially the car drove straight when the hash mark on the wheel at the 12 o'clock position was oriented directly upward at 12 o'clock. After the turn I described, the dead ahead position of the steering wheel with hash mark at 12 o'clock would make the car turn left as if I were trying to change lanes to the left. To track straight ahead, I had to make right steering input of what I estimate to be 2 degrees. This was evident with the red hash mark on my steering wheel being oriented right of center when traveling straight ahead.

I hear what you're saying about the paper specs vs what I was experiencing.

For whatever it's worth, here is what Gemini thought of that alignment and my real-world experience of a left pull, right correction on the wheel. To Gemini's point, I'd say the car was darty, unpredictable and required varying amounts of correction at any moment in time to travel dead ahead. And our roads have lots of crown and tire ruts, so the Z06 is always a PITA as it seeks around the lane. Gemini's last line seems to explain it best.


Gemini:There is a technical reason why your real-world experience (pulling left, wheel right) contradicts the typical "paper" logic of that printout.

The key lies in the Front Toe and the Caster relationship.

1. The "Toe-Out" Instability

Your front right toe is -0.75° (significant toe-out).

1. When a wheel is toed-out, it wants to turn outward (away from the center of the car).
   
2. In your case, the right front tire is "prodding" the car toward the right, but it is also creating massive drag.
   
3. If the left front tire has more "bite" or a more aggressive grip angle, the car can sometimes "dart" or "wander" toward the side with more stability, which in this setup is your left.
   

2. Caster and Road Crown

You have a Caster imbalance: 8.4° (Left) vs 8.1° (Right).

1. Generally, a car pulls toward the side with less caster. Your right side has less caster, which reinforces a right-hand pull.
   
2. However, if you were driving on a road with a heavy "crown" (sloped to the right for drainage), and your front toe is as messy as it is here, the car becomes hyper-sensitive to road inputs. If the suspension was "loading" the left side more heavily due to that -1.34° rear toe, it can override the camber/caster logic.
   

3. The "Steer Ahead" Reality

The report shows a 0.77° Steer Ahead.

1. This means that for the machine to "see" the wheels as straight, it thinks the steering wheel should be turned.
   
2. If your wheel was angled to the right while the car pulled left, it suggests that you were actively "fighting" a leftward drift caused by the rear end "dog-tracking."
   
3. Because your Total Rear Toe is -1.06° (toed out), the rear of the car is incredibly unstable. This creates "Rear Steer." If the rear tires are fighting each other, the car will often take the path of least resistance, which is often the direction of the most aggressive "out-of-spec" tire.
   

Summary of the Paradox

The reason it feels backwards is likely Total Toe Instability. When both the front and rear have such high negative toe values (toe-out), the car loses its "centering" force. Instead of a "pull," you're likely experiencing a "drift" where the car follows the rear axle's geometry, which is heavily skewed toward pushing the chassis leftward.

 

You can see (on his alignment sheet) how far off the toe was off - meaning that the alignment slipped significantly.
Spearfish, did your tech know to torque the bolts 90 degrees past 111 ft/lbs?
I get mine aligned at the Chevy dealer and the Corvette tech knows to do this. Thankfully, I haven't had this problem after the one time it slipped last year.
I wouldn't abandon the C8Z platform because of this, since the problem can be fixed by torquing properly or using the AMT kit.

 

Ok, so you don't really have a pull...you have a steering wheel that is off center. Since that was caused by a one time event (the turn you took), it could have been caused by slippage of one of the eccentric cams causing the alignment to go out of spec, or less likely a bent suspension part. I assume the alignment got the steering wheel back on center. I wouldn't make too much of it. Now that the car is aligned and the wheel is straight, drive it and enjoy it. If it happens again, tell your alignment guy to tighten those eccentric bolts a bit tighter lol.

By the way, small differences in any alignment angle can be simply caused by equipment variation or setup variation. In other words, if you take a car in and have it set up on an alignment rack, print out the measurements, take the car off that alignment rack, take it back the next day and have a different mechanic (or even the same mechanic for that matter) set the car up on the exact same alignment rack, and print out the measurements before doing any adjustments, the measurements will be very close, but likely will not be exactly the same.

 

Admittedly I don't know how the toe is set on a C8, but let's assume it's set like most other cars with a tie rod and a jam nut. If so, it's very unlikely that toe itself would "slip". More likely is that the eccentric cams that are used to adjust caster or camber slipped, and this will in turn impact toe...which is what I alluded to above.