Mad Dog 24

Just ran across this picture from last fall. For those new to your C7 the rear caster is adjustable on your car. Very few cars have this adjustment, Saturn Solstice is one other. This was our rear caster after lowering the car and alignment. GM suggest 0 degrees ours with 90 being 0 was off more than 2 degrees! Street cars not to worry but if your tracking the car get your caster checked. Many dealers do not have the bracket to adjust or even understand it. Check before you waste your dollars.

z51vett

Dealers may have it but does tech know how to use it.
z51vett
Doug

FastestBusaAround

Didn't the C6 Z have it as well?

bryberg

Dealership tech here. That measurement is being taken incorrectly. The wrong tool is being used. The mounting bracket is correct, but you need a gauge that measures in relation to the alignment rack. The correct tool has a base that attaches to the rack, connected by wire to a sensor that attaches to the mounting bracket. The measurement in the photo is probably pretty close, but if floor has isn't PERFECTLY level, the reading will be off.

z51vett

Well where do you work you just might have more business than you want.
z51vett
Doug

5thGear

Thanks for sharing this info with us.
Dealer did my track alignment so I have to look into it. They handed me 8 washer (removed to get the right camber I was told). Does this sound right?
Attaching my alignment sheet <br >

bryberg

They took too many washers out, you are only supposed to remove 1 washers from each front lower control arm bolt, 4 total, and none from the rear suspension. The numbers are pretty close, front caster is .4 too positive, needs to be 7.0 on both sides. Rear camber is .10 off, needs to be 2.0, rear caster won't show up on a printout, but needs to be 0 for track usage.

These specifications are only for track use, need to be switched back when you're done at the track, unless you like buying tires.

5thGear

Thanks for the info.
I just read the manual and it doesn't say to take the washers out of the front only. Also, each of the upper control arms have four bolts (connecting to the frame) so if they take only the front washers out then there would be 8 washers total. If they take one washer out from the front and rear then there should be 16 washers total. I could be wrong. I really have to look into it and see what others have to say.

BEZ06

Well...you're a dealer tech, so I know when you review that you'll realize you made a mistake in that analysis.

The LOWER Control Arms are attached with eccentric cam bolts in order to move the LCA's in/out to adjust the camber/caster.

The UPPER Control Arms are attached such that washers can be removed to move the UCA's inward - and that will increase negative camber.

The 2016 Owner's Manual says:
There's absolutely NO mention of removing washers from the FRONT ONLY. You can remove washers from the rear UCA dogbones that attach the UCA's to the frame, and that's the only way to get as much camber as you might want for track driving.

Here's a picture of my old C6 Z06 I traded in on my C7 Z06, but the UCA's are exactly the same - and you can see that the dogbones are attached with 2 bolts, i.e., 4 bolts per corner of the car; 16 bolts total:




Below you can see some washers between the dogbone and the frame. Just as on the C6, when adjusting the C7 camber you may need to remove a washer in order to increase negative camber to your track spec:




The 2016 Owner's Manual also says:

As it says, "Alignment values are targets". There are WIDE tolerances in the specs in the Service Manual.

For Ali_Z06's alignment, front caster is excellent - it's the same both sides and well within spec, and not worth distorting front camber and toe to get less. It's the same both sides, but normal street alignments often call for different caster left and right for better tracking down crowned/sloped roadways. For the track I like the same both sides, but am happy with "close" - i.e., not more than 0.4* difference between right and left caster settings.

I think there's nothing at all wrong with Ali_Z06's rear camber - it's going to be well within the WIDE dealer specs, and was probably the max negative camber they could achieve be cranking the LCA eccentrics all the way out and removing only one washer from each rear UCA dogbone bolt. There are 2 bolts on each UCA dogbone, and 2 dogbones - therefore 4 bolts per side. I'm pretty sure that the 8 wahsers they gave him probably came from the 8 rear UCA bolts.

The problem I see with his track alignment are the toe settings. It looks like he's got Zero toe front and rear. Many of us track rats like a very slight toe-OUT up front for better turn-in. And, you pretty much MUST have some toe-IN for the rear for better stability when getting on the throttle as you track-out of turns. The rear end can be very squirrely with toe-out, or even Zero toe, at the rear wheels.

Finally, there have been a couple performance shops that have analyzed the rear toe-change (the toe-curve) on the C7 with shock compression/rebound. There's quite a bit of bump steer (toe change) with shock movement. It seems to have a much more acceptable toe-curve with a bit of positive rear caster. The GM rear caster spec is -0.8 to +0.8, which is of course a ridiculously wide range. The track alignment recommended in the Owner's Manual is Zero rear caster, but the performance shops' recommendations are that a bit of positive rear caster gives a lot better toe-curve to reduce bump steer. I'm going to set my C7 Z06 up with about +0.8 rear caster for the track. At least one forum member says that really improved the rear end stability.

Bottom line - Ali-Z06, I like your alignment except for the toe settings, and I'd get your rear caster checked and set to Zero or slightly positive.

Have fun at the track!!

5thGear

Thanks a lot for all the detailed info. I will have a the toe adjusted and rear caster checked.
Heading to Spring mountain next weekend to run the 3.1 mile course (The Hunt). After that will check the alignment again and will be at Auto Club speedway first week of May. Thanks again.

BEZ06

Sounds like that should be a lot of fun!!

You may have seen this long thread, but it may be worth another look:

https://www.corvetteforum.com/forums...alignment.html


Take a look at Poor-sha's posts# 14 & 17 to see that he really liked his car set up with a little positive rear caster.

Tech Contributor Bill Dearborn's post# 41 is very interesting, and Schaibaa's post# 42 has some good info about bump steer, the toe curve, and camber and toe for his track set up.


.

Mad Dog 24

ACTUALLY the tool when used properly does all it needs to do. We first start by zeroing it off the alignment deck so yes the numbers are accurate. For those that don't have a full alignment rack this tool will also do front caster sweeps. Used in NASCAR regularly so good enough for our cars. The GM digital gauge ($900!!!?) is crazy priced and in the end just easier to read while adjusting. The bracket is cheap, $110.

While your here GM tech... to be clear a positive rear caster is the upper CA is back correct? We were planning on going .8 caster in the rear before our next track weekend. As others have tried it seems to be the ticket!

schaibaa

Yes sorry mad dog I had incorrectly quoted negative rear caster but positive 0.8-1.0 seems to be the sweet spot. This means the spindle lays back, lower ball joint foreword of the upper ball joint.

tracer3030

I had to weld up the cam for the right rear toe cam bolt to get the toe right with 2 deg camber. The slot was long enough for the adjustment. I did not take the upper control arm washers out in the rear

Mad Dog 24

I'm not following you on the welding of the cam can you post some pics and why just one side an issue?

Schaibaa, 1.0 caster in the rear sounds like a lot. Have you or anyone else tried that much? For what its worth, mine has been at least 2.0 positive caster and .02 toe for the last 4k miles driven hard with one fall track day at that number without checking caster. I must say it tracked well enough that myself or my "pro" driver did not experience anything out of the ordinary. I'm wondering if the 2.0 is creating even more toe "in" under compression for the rear which usually helps when your back on the throttle. Your thoughts..... Are we on to something this adjustable rear caster my be our friend!

Where's the other track nuts?

Bill Dearborn

You aren't familiar with this particular tool. Like the gage that GM calls for it can be zeroed to the rack. It has a zero adjustment feature that permits that setting. The only thing is the zero is set at zero degrees horizontal so when you make this reading you are looking at 90 degrees as being equivalent to 0. I have this gage and I am waiting for delivery of the bracket. The biggest issue I have run into when holding my gage up to the bosses in the knuckle withouut using the bracket is reading the direction of the caster. The gage has arrows to indicate direction but they are hard to see from the angle shown. My goal is to get the caster close to zero on each side and not worry about + or - since GM doesn't specify a cross caster setting.

If I go to any of the local dealerships I have to take my gage and bracket with me and show the mechanics how to use them since none of them know about the caster adjustment.

Bill

Bill Dearborn

While trying to find a dealership that could do the rear caster setting I got a copy of the latest GM Tech Bulletin on doing the track alignment. It says that on the Z06 you can only remove one shim (washer) from the front. Not the rear. I am not sure why but when I look at my car I see two shims behind each front UCA and only one behind the rear UCAs. They may want those shims in place for some other reason besides alignment. I asked several mechanics and they had no answer to the question, just the typical deer in the headlights look.

I attached the Tech Bulletin to this post.

Bill

RapidC84B

Alignment settings don't need to be exact... just eating a heavy meal and sitting in the car will change things on all the gauges. Most of us string align our racecars and don't get nearly the precision of the fancy digital readouts. Don't sweat a little imbalance here and there.

Don't worry about washers... they're usually behind the UCAs. I've found many cars that had uneven amounts from the factory to account for slight frame variance. I always count how many are there to start (if I know the car has never been touched) and remove equal amounts. Normally we end up removing all of them shooting for around -3 degrees front camber running Hoosiers. We install blocks in the LCAs to move them out and lock them in place as the eccentrics can move on race tires.

BEZ06

Thanks for that info, Bill. It's very curious that you can remove a washer from the rear on the Z51 but not the Z06!

I removed all of them on my C6 Z06 and never had any problems. I'll probably do whatever I need to do on my C7 Z06 to get the alignment I want.

I believe I've read here on the forum that if you do remove washers on the rear of the Z06 that you may have problems being able to adjust the rear toe into spec.

I don't like that eccentric toe adjustment - I'd much prefer to have a normal toe link that you can adjust by turning the tie rod. It looked like Baer was going to make one, but apparently they never made it available for purchase.

Bob

Bill Dearborn

Agree, they don't need to be exact. But it would be nice to know if they are in the ballpark. If you don't have the tools required to make the measurement it is hard to know. GM got people wondering about this after the Randy Pobst test drive at Laguna Seca where he complained about corner exit handling. GM said the rear caster had to be corrected and when Randy retested the car it handled much better. None of us on this forum are close to his driving skill level but it does make a person wonder if Randy had an issue would somebody with less skills have more of an issue?

Bill