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Alignment advice - Z06

Old 10-11-2018, 12:13 PM
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NineVettes
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Default Alignment advice - Z06

I have the DSC recommended alignment specs but it seems that rear caster is exceptionally important on these cars. Supposedly, the ONLY way to set rear caster on these cars is with this nearly "unobtainium"GM Tool #CH47960-10 which costs over $750. Local Chevy dealers cannot or do not want to do. Local Alignment Shop with superb reputation does not have this tool, but claims he has done C7's including Z06s without it.

Can the caster be set accurately ANY OTHER WAY without using this particular tool?

Recommendations?

Thanks!
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Old 10-11-2018, 01:09 PM
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Mr. Gizmo
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Will be interested in hearing from the experts on this. FWIW, I had a street alignment done in my 2017 at the 500 mile oil change. I donít think the caster was done . Car tracks smooth and straight and doesnít get too squirrelly with hard acceleration
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Old 10-11-2018, 02:47 PM
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Bill Dearborn
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Originally Posted by NineVettes View Post
I have the DSC recommended alignment specs but it seems that rear caster is exceptionally important on these cars. Supposedly, the ONLY way to set rear caster on these cars is with this nearly "unobtainium"GM Tool #CH47960-10 which costs over $750. Local Chevy dealers cannot or do not want to do. Local Alignment Shop with superb reputation does not have this tool, but claims he has done C7's including Z06s without it.

Can the caster be set accurately ANY OTHER WAY without using this particular tool?

Recommendations?

Thanks!
First, GM has a program to loan the proper tools to any dealer who wants to borrow them.
Second, the expensive tool is the CH-47960 not the CH-47960-10. The -10 is the adapter that adapts the CH-47960 so it can fit the C7. The gauge wasn't designed for the C7 it was designed for the Pontiac Solstice/Saturn Skye. The CH79760-10 can be purchased directly from this supplier: https://gmtoolsandequipment.com/en-U...KU=CH-47960-10

You can use a magnetic saw blade angle tool to measure the rear caster using the above adapter. Just make sure the one you purchase has a +/- 0.1 degree accuracy. To use the gauge you need to zero it to the alignment rack/floor on both the left and right sides of the car. This follows the procedure defined for the GM gauge which is zeroed for each side of the car.

Some people use two quarter inch bolts stuck into the holes in the knuckle and use their iPhones angle measurement feature to measure rear caster. There are two concerns I have with that. First, is there any difference in the vertical plane defined by the two bolts and the vertical plane that is part of the actual GM adapter? Second, how accurate is the iPhone angle measurement feature? We are talking about a measurement that can vary between -0.8 degrees and +0.8 degrees. Any what would seem like a small error could be huge on that scale. I did some searching in the App Store and found an App that says it is accurate to +/- 0.2 to 0.3 degrees depending on the device it is used on. That sort of indicates the phone may not be accurate enough for the task.

I am attaching the GM February 2016 TSB telling dealers how to perform the track alignment. You don't have to use the numbers they define but it is best to follow the procedure so you are sure you get what you want. The rear caster adjustment is also defined in the factory service manual for each year of the C7 along with the recommended street settings.

Bill


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Old 10-12-2018, 11:20 AM
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In a thread Poor-sha posted saying you can have 1 extra washer behind your rear upper control arm which will set the rear caster to a static positive value? Is this still valid? I did this on my car and the car feels great coming out of corners.
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Old 10-12-2018, 02:50 PM
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Originally Posted by 2005vetteTT View Post
In a thread Poor-sha posted saying you can have 1 extra washer behind your rear upper control arm which will set the rear caster to a static positive value? Is this still valid? I did this on my car and the car feels great coming out of corners.
Too a certain extent that is true. However, both camber and caster are affected by placement of both the UCA and the LCA. To make it so the UCA provides a positive caster bias you have to remember that shim is only added behind the front dog bone and not the rear. If you added shims behind both dog bones then you did nothing for caster and just reduced camber. It also depends on how the lower control arm is adjusted as well. If the LCA is adjusted so the ball joint of the control arm is pushed to the rear that will provide a negative caster that will offset the UCA. Everything is interdependent. Increasing positive caster using the front dog bone of the UCA will reduce negative camber, Increasing positive caster using the rear cam of the LCA will increase negative camber.

Bill
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Old 10-12-2018, 03:57 PM
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Originally Posted by Bill Dearborn View Post
Too a certain extent that is true. However, both camber and caster are affected by placement of both the UCA and the LCA. To make it so the UCA provides a positive caster bias you have to remember that shim is only added behind the front dog bone and not the rear. If you added shims behind both dog bones then you did nothing for caster and just reduced camber. It also depends on how the lower control arm is adjusted as well. If the LCA is adjusted so the ball joint of the control arm is pushed to the rear that will provide a negative caster that will offset the UCA. Everything is interdependent. Increasing positive caster using the front dog bone of the UCA will reduce negative camber, Increasing positive caster using the rear cam of the LCA will increase negative camber.

Bill
This makes sense - I see why he said to only manipulate the camber via shims on the UCA and leave the LCA then. If my LCA has been adjusted for camber, is it safe to say I'm going to have to get the angle gauge to get a proper reading?
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Old 10-15-2018, 03:25 PM
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Keep in mind that the '17's and newer do not need to have the shims removed from the control arms.

http://www.corvetteactioncenter.com/...2017-1350.html

Last edited by IM4A2Z; Yesterday at 11:10 AM.
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