This morning I took my '19 to who was considered the best alignment guy in my area. He uses a Hunter machine. Tire inflation checked and are at 30 lbs all around. I wanted to try to set specs to the DSC "Street/Occasional Track" specs. The following readings are in degrees. My original alignment read out was as follows: Left Front: Camber -1.0, Caster +7.4, Toe +0.07, Right Front: Camber -1.1, Caster +7.8, Toe +0.05 Front Total toe +0.12 Steer Ahead +.0.01 Left Rear: Camber: -1.0, Toe -0.07, Right Rear: Camber -1.5, Toe -0.06. Rear Total Toe -0.13, Thrust Angle -0.01

New alignment read out is: Left Front: Camber -1.3, Caster +7.4, Toe -0.07, Right Front: Camber -1.2, Caster +7.8, Toe -0.07, Front Total Toe -0.14, Steer Ahead 0.00
Left Rear: Camber -1.3, Toe -.07, Right Rear: Camber -1.3, Toe -0.07, Rear Total Toe -0.14, Thrust Angle 0.00.

So I am driving home, and depending on the road surface (maybe some roads have grooves or crowned) the car jerks violently to the right even under moderate braking. Feels like it is coming mostly from the rear, but not 100% sure. On local interstate, this did not happen with moderate braking. But car is now borderline safe to drive. Car tracks well on acceleration, braking seems to be the issue, violent on some roads... On the Hunter printout, the left front & right front toe readings are highlighted RED as is the Total Toe.

Called the guy back and he says he thinks it is the front toe which was originally positive and now negative. Those readings are in degrees, DSC specs are in mm for Toe?

I am going to take the car back on Thursday. Is the new toe settings the culprit here? Differences between degrees and MM?

Not sure if he changed rear caster at all - no measurement tool (he could not use my angle gauge)

Looking for suggestions from resident techies and racers...

Thanks

 

Conversion between mm and degrees = https://www.corvetteforum.com/forums...n-degrees.html For what its worth. the .07 degrees is really close.


Initial thoughts on your specific alignment.... I dont like the cross camber and cross caster differences up front. I always want them even. Yours isnt terrible, but its not perfect either.

Secondly, its possible to get rear camber in spec, and have caster be WAY out. Moving mine around on the alignment machine, you could get camber in spec and have 3 or 4 degrees of caster in the rear which is a massive change from where factory wants it. This would be my initial guess on whats going on with your car.

 

EASIER TO READ FORMAT FOR YOU (US)

BEFORE

FRONT :
Camber -1.0, -1.1
Caster +7.4 +7.8
Toe +0.07º +0.05º
REAR:
Camber -1.0, -1.5
Caster ? ?
Toe -0.07º -0.06

AFTER
FRONT :
Camber -1.3, -1.2
Caster +7.4 +7.8
Toe -0.07º -0.07º
REAR:
Camber -1.3, -1.3
Caster ? ?
Toe -0.07º -0.07

 

Having front toe out will increase wander on irregular road surfaces. You had a slight toe in before and have a slight toe out now. It might be an issue but is hard to say. Steering pulls toward the side with the most positive camber and toward the side with the least positive caster. Your current settings should provide a slight camber pull to the left along with a slight caster pull to the left which just might let the car steer straight when riding on the right side of the road crown.

Did the guy tell you why he couldn't use your angle gauge to measure rear caster? It is a fairly simple thing to do with a lot of us forum member morons able to do it. It seems like any well trained and knowledgeable alignment guy should have been able to use the gauge. Or is it they didn't believe there was such a thing as rear caster? However, I am not sure that if rear caster was way out of whack it would cause the pull you are getting under light braking. Rear caster is used to counteract bump steer and you shouldn't be having that much suspension movement with light braking to get bump steer.

Right now the only thing to do is to go with the front toe adjustment and have it set like it was previously. I would also talk to them about measuring rear caster and adjusting it. What type of gauge do you have and do you have the GM Gauge adapter? If you don't have the gauge adapter supposedly two quarter inch bolts will fit in the holes and provide a reference for a gauge like an iPhone if you have the angle gauge app on the phone.

When adjusting rear camber and caster I believe the front arm of the lca affects caster more than it does camber and the rear arm of the lca affects camber more than it does caster.

Bill

 

Sounds like exactly what happened with my car. It was ok to begin with but I read a lot of horror stories of alignment being out of wack from the start so I took it in to get aligned. They informed me AFTER they were done that the Corvette "doesn't have an adjustable rear caster" and after that day under acceleration or even divits in the road the cars rear end gets very loose. It's definitely a rear caster issue and I am hoping to have mine fixed soon.

 

Thanks for the responses, guys. I was just trying to get the car baselined - the other day got the required GM 500 mile oil change, kept it below 3500 RPM until then and was happy to see the Yellow warning line disappear on the tach. Putting the Level 2 Aero on the car, finished the rear myself but will need the car up before the front pieces go on. Most of the new Vettes I bought were somewhat off on alignment, and this time I thought "why not use the DSC Street/Occasional Track settings" as a new baseline.

Now, in light to moderate braking except on the local interstate, the car is evil - always jerking sharply to the right, I guess because of a crowned road. I asked the guy to use my angle gauge (one of the ones Bill recommended I buy and I do NOT have the GM gauge adapter - I didn't think GM sold it to the public)) and he said he does not have any attachment tool for it and anyway, after aligning corvettes for over twenty years (including Corvettes) I am the first guy to ask him about setting rear caster. I am pretty new to this area, but this shop came very highly recommended to me from several sources in this area.

He also suggested just going back to the original toe adjustment I don't see any problems with the camber front and rear - agree? I will try to get him even out the front caster settings. I still do not understand why the recommended DSC toe settings (he set mine pretty close to them) are causing this severe problem? How could these settings wreak so much braking havoc? Pretty unsettling!

 

It isn't the settings you have now, it's the rear caster that was changed by him changing the other settings. If he doesn't adjust the rear caster along with everything else it's going to be out and that's what's causing my problems that sound a lot like yours.

 

The small gauges won't work unless you have the adapter. Did you provide him with the GM Track Alignment TSB (attached) that shows how to measure rear caster? It can take several weeks to get the GM Adapter if Bosch Tools is out of stock. Order it here: https://gmtoolsandequipment.com/en-U...KU=CH-47960-10

However, if you can't get it quickly try using two quarter inch bolts stuck in the adapter holes in the knuckle and an iPhone bridged across the bolts to measure the angle. I don't know if the iPhone is accurate enough but it will get you in the ball park. One of the key things is to remember to zero the gauge to the level of each side of the car. Zero it to the alignment rack on the driver's side when doing the driver's side measurement and then zero it to the passenger's side of the alignment rack when doing the passenger side measurement. If zero'd properly then you don't need to do any additions or subtractions to understand the measurement. It will be displayed in the units you need.

Bill

 

Well, I will be going back to the shop this Thursday. I think, based on what I am hearing, Step 1 is to go back to the original front toe settings (rear seems to have not changed). Possible Step 2 is to even out the front caster to 7.4 where now it is 7.4 on one side, 7.8 on the other. If I can get the guy to look at rear caster with either the angle measurement tool I bought OR an iPhone App, we can look at that. If he won't do it and the car remains evil - well I will cross that bridge then??

 

Bill, just saw this. I will provide him with this info. Thanks!

 

I will be interested in seeing/reading the response of the excellent alignment shop that hasn't kept up with the most recent Corvette Stingray ability to set rear caster.* Either he will be surprised and gracious, or .... well, we'll see.

* I believe it's now been around for at least a few years, if not longer. Bill D can correct me.

 

I suspect most alignment shops have no knowledge of the requirement. How many align C7s? The number of cars isn't that high and the number of people looking to get the alignment done is much less so not many shops know about it. Even GM Service people have to be instructed to read their own service material. The Corvette mechanic at the dealership where I get my car worked on didn't know about it until I started asking him. Then he looked it up but the Service Manager refused to spring for the equipment to align just one car although they had sold several C7s. The body shop where my Z06 is being repaired after nailing the wall at VIR didn't know about it. I told them I had the tools and could show them how to measure/adjust the caster as it will need to be done since the right rear UCA, LCA, Knuckle, Hub and toe link were all replaced.

Bill

 

Hi Bill,
Technically, shouldn't it pull slightly to the right since the right side camber is closer to zero (LF=-1.3, RF=-1.2)? Or did you mean to say the most negative camber?

 

OP, 90% chance its the rear castor. Frankly I cannot believe a shop would even attempt to align a C7 without having the capabilities of checking\adjusting rear castor. While you notice this issue under braking I may have an explanation. These cars have a progressive rear toe curve. When the back of the car goes up as in braking or down when under acceleration the rear toe moves in and out. So, if your car has a positive rear caster on one side and a negative (upper rear ball joint leaning forward) on the other side the car will react just as you described. One side the rear will be toeing out and the other toeing in at the same time! If you can imagine this will move the rear to that side almost like rear steering!

I hope this helps explain this and be careful until its been fixed. I will monitor this thread in the case you find something else. Your final toe specs and everything else does not seem to be the issue to me. Just to eliminate the possibility have the brake calipers checks to make sure clamping pressures are similar. A bit of air \water in one caliper can cause a pull. Good luck!

 

Yup. This is exactly what I was saying. Definitely the rear caster because I am experiencing the exact same thing.

 

Been incredibly busy at work recently, so just getting back to updating my original posts. Late last week, went back to the alignment shop and now the evil (borderline dangerous) handling problems with my '19 Z are totally resolved. Per Bill's advice, I downloaded the Rigid Tools Level app onto my iPhone 8 Plus, picked up the 1/4 inch bolts and used that to help set rear caster (which was way wacked) as well as redoing other settings such as moving front toe from negative settings to very slight positive. The alignment shop (considered the best in the area) had previously done a number of C7's but had never been asked before to address rear caster. It took a bit of time to get a level of comfort using the iPhone App and bolts plus doing several readjustments, but the car is now dead ***** on for the street, and will have a very mild track oriented setting for my occasional forays to the track. And the alignment guy confessed that after doing this for over twenty years, he does not often learn new things from his customers, but he did that day! He is going to use my settings as a recommended base for his C7 Z customers.

Thanks to everyone who contributed and helped, especially Bill Dearborn.