Let's start our discussion here...

Assumptions:
corner weights are set
ride height is set
floor is flat
suspension stichion is removed by slip plates or roll-off rig or other method
correct air pressure in tires. New tires are best.
sway bars disconnected

 

First sorry for the pictures they are out of order pulled from various places and have some omissions but the theory holds.

The items here are all I use to align. They fit in a very small place and are easy to take to the track for a quick alignment change or repair if say you knock out your toe going off track.

The "L" is cut to the exact size of my 18" wheel edge

 

I'm working on a lift but you can do this other ways too. Floor is level you can see some of the 1/8" flooring tiles used to get floor flat. 3/16" steel greased slip plates are used because my pea brain thinks the plates will not flex for more friction and the grease will let them slide. Car is corner balanced and yes my car is a pig for my race class with 1/2 of my fuel load estimated during my next race.

A trick to absolutely know if you have your suspension settled is after you let the car back down on the lift is if the corner weights are the same. The steel slip plates work really well for me because I can get exact corner weights to the pound upon settling. I'm not sure if it matters but I'm running a delrin suspension that settles. My OEM rubber suspension was all over the place.

 

Typically, you would want to set thrust first. Everything starts with back wheels pointing in a direction so the chassis is not dogtracking down the track. But the Vette is weird. Camber change dramatically effects the thrust. So set the rear camber first. My class rules changed so I had to reset camber. I was going to just use the adjustable cams and forgo the solid plates because I'm lazy, have to order them, hardbar is MIA, and pfadt is outta bussiness. But once you realize how much a moving camber plate can effect your rear toe it is down right scary. When rear cam locks move it is not the camber chance that makes your car undriveable but the radically changing rear toe and chassis thrust.

So I broke down and made some camber plates out of simple aluminum bar stock. The trick was setting the camber with the camlocks. Then carefully measuring the camlocks on the car and making the shims to that size. That was not totally accurate but got me within about 0.1* of where I wanted to be.

Sorry for the fabrication segway but the camber moving is so unsafe I really feel strongly enough about it to go to all the trouble of making the shims. So here is how to make them yourselves.

 

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So you use the bubble and zero the laser level. Then you place the "L" on the wheel and measure the camber on the digital level. Do this on slip plates. Picture just to show position and it is lame as I tried to hold all that stuff with one hand and shoot the photo in the other. Note my picture also has the L not on both rims of the wheel. It must be exact but you get the idea...

 

Keep it coming!

First question: could you not get the same measurement of rear camber without the L? Just use a straight edge sized to the wheel and hold the digital level vertically?

 

Now measure the Thrust. This is done with the same "L" cut to size for your wheel. The laser level has a notch in it that slides right into the "L" and you shoot the laser down the side of the car measuring the ruled distance from the front hub center. You want this to be the same on both sides. If you do the math you will find this is extremely accurate because a tiny off at the rear makes for a huge off at the front. 1/2* off at the rear magnifys itself over the 100: wheelbase to visually almost 1"! So lets say you can easily see the ruler at the front hub to +/- 1/8" (which would be very sloppy work) that would mean your thrust would be off 0.07* per side. That is pretty darn accurate.

sidenote: the ruler you see must be level. Small deviations as the ruller rotates around an arc with central point as the hub will change the reading on the ruler. I'm on slip plates on front too and flat. Yes it is that accurate and it makes a difference.

 

I fix the ruler with a contraption like this on a jackstand and the ruler is level and on the hubface.

 

Once thrust is done I adjust rear toe. Then I adjust front toe. I was skeptical about not putting toe plates or something like strings measuring directly to the wheel face. I did not like the fact that Toe plates rest on the tire face not the wheel face. I had fears of poor accuracy when measuring from plates on rubber. However, I took new mounted hoosiers and placed a straight edge accross the tire and measured from tire to wheel 180* apart. With the tools I have I could measure no problems with toe plates on tires. So I accept using toe plates. Still I'm on slip plates and leveled floor and two identical tapes. I guess that makes sense. I mount my own tires and the tires are so well made today that a straight wheel and new tire can be used unbalanced but that's for another thread.

Off to the side you see my scales set to corner weights so each time I move the car to make an adjustment I can get the exact same weight upon settling the suspension.

 

my method for thrust angle is similar
here are some of my tools
laser level mounted on a jackstand with an angle to make sure it is longer than the sidewalls

 

magnet on ruler mounted with an L bracket.
round magnet from Harbor freight sets on hub flange

 

I use smart strings to set toe, i center the strings by measuring the string to axel shaft ends in the rear with a digital caliper (the depth measuring probe) this allows me to adjust to .01 MM. the actual toe I measure to the rim flange with the same caliper.
on the front I measure to the flange on the hub.

 

Here is a shot of my corner weights with a full tank and the drivers seat weighted to my weight

 

Mine is all on video, one for camber & another for toe so I can't easily post pics, but I'll just pop a few questions off here and there & maybe add to the discussion.

I thought that thrust was more of an axle to axle measurement?

If you measure off the rear wheels or tires to the front axle the rear toe (which could be off a little at the start of the alignment) is going to mess with the thrust check.

I could see checking it at the END to confirm it's ok.

As for the camber it's pretty straight forward. The Smart Camber tool is just a digital level mounted in a frame that adjusts to different rim sizes. The "secret" IMO of using any digital level is that you can calibrate it, which Smart Camber has a (somewhat involved) procedure to do. I calibrate every time I use it.

I also have the Craftsman digital level. I don't recall if it has a calibrate feature? Does it?



My slip plates are 2 Home Depot bags (4 thicknesses of plastic) which slip really great. Those are on a flat (slippery white finish) particle board cut to fit on my ramp top & let the tire rotate clear of any edges of the ramp.

 

I don't know what it is. I think of it as front and rear axle square with chassis centerline. Maybe what you are saying means the same thing. I knew nothing about strings before I saw your video. What I am thinking is strings save time? Am I correct in understanding that setting rear toe with strings is setting the thrust to zero as a byproduct of setting rear toe? My method takes more time 2 steps. In my method you set thrust by adjusting toe to whatever it needs to be on one rear wheel to get equal measurements to zero the thrust "then" you adjust toe again on both rear wheels to get desired toe in or toe out.

Maybe I place too much importance on equal right and left turns and thus a zero thrust. I wonder about the relative accuracy of strings where you are measuring from front lip to string and rear lip to string over only 18" while I set thrust over the 100" wheel base. I think I got you beat on accuracy but perhaps accuracy here is not that important? I place emphasis on thrust due to my own bias from science backround. One small error at the start magnifys itself as the process evolves.

Perhaps a good test would be to sort of use a hybrid approach like Ernie with stings and a laser. When I read his method I first thought...if Ernie is using strings why the laser if strings can do thrust? But maybe until we amateurs can confirm alignment science doing strings for thrust first and "faster" (killing two birds with one stone) then confirm thrust with the laser make sense. Once proven that measure over 18" is as good as measure over 100" then ditch the laser if you want to save time and effort.

 

Yes you can calibrate the craftsman level. It is fast and easy and presumed accurate. You set zero on the level by using the level's bubble to gain perfect horizontal then press the "zero" button on the level. I have confirmed that is how it works by other gyrations I won't explain here. Then the "L" rule cut to fit my wheel is similar to the smart camber but of course the smart camber is adjustable and self contained but can't be used to help me set thrust and project a laser.

For slip plates the only requirement is removing stichion. So anything that achieves that is good. I chose thick steel greased plates because I was thinking about how I work. lifting the car up and down on a lift and the bags blow and I'm chasing them around the garage. I was concerned about debris acting like friction. Nothing can get between the plates. I chose thick steel to reduce flexing over surface irregularities to prevent bending of the plates introducing friction between the plates. Overkill is very likely. I still like a fixed plate and for easy and lightness perhaps I would try sheets of plexiglass if I were doing it again. I am not a fan of sand between plates or bags. I have only gained confidence in my slip plates and delrin suspension once I could confirm reproducible corner weights. When my suspension was rubber the suspension stichion was a real bear. Corner weighting a car with rubber bushings was an exercise in "hoping you got close." Now any error is because I screwed up.

 

Ernie,

If you are using strings why measure thrust with the laser?

 

It probably is for a track only car. Mine is a daily driver too and accumulates over 20,000 per year as such I am fussy about tire wear

 

Yes you can. As long as your laser level has the ability to measure that way and be "zeroed" that way. The other issue is level are more accurate if longer. If you take a level to a jobsite and use long vs. short levels you see what I mean. Sometimes you will see people fastening a short level to a long straight edge to simulate a long body level to gain accuracy.