Castor measurements confusing

[nreed]

Ok I'm kinda feeling my way with DIY alignment. I am using a Smart Camber gauge. (and I calibrated it). I took one set of measurements:

Height at front fender 25 inches.

Wheels Straight - Camber = -0.4 deg
Front of wheel 20 deg out from chassis - Camber = +3 deg
Front of wheel 20 deg in toward chassis - Camber = -2.4 deg

Add these two numbers and multiply by 1.5: answer = 8.1 deg castor

Now the weird part:

I moved the top of the strut .5 inch toward the front of the car for less positive castor and I get the same numbers.

What am I doing wrong?

[WinRice]

Norm,

How are you measuring the 20 degrees each side, with turn plates? Are they free to move in all directions? If they're not, and the suspension is binding, it'll give erroneous readings.

Before I bought good turnplates, I used the highest load ballbearing turntables I could find at a wood supply store with a square of 3/4" plywood top and bottom. Then set those on eight old V8 pushrods per each wheel to allow lateral movement. Worked pretty well.

Another option, is to get a few squares of cheap linoleum floor tile at the local home store and put a little thick axle grease between a couple to allow movement. It can get a little messy though.

Forgot another thing, are you holding the SmartCamber perfectly vertical? I hold a small torpedo level to the side of the SmartCamber frame to check.

[nreed]

Thanks, I've got some floor tiles and I'll use a level as you suggest. The thing I just can't figure out is that I get EXACTLY the same numbers after I move the top of the strut forward.

I've got Elephant adjustable front camber plates and poly-bronze bearings in low friction mounts.

[WinRice]

If you figure a compressed strut is roughly 22" long, a 1/2" of movement at the top is about a 1.3 degree change.