Adjusting the caster will change the camber. When you shim the UCA you are moving its mounting point outward, which is increasing negative camber. The problem with the way the '65-'66 cars are done is that you have to compromise between caster and camber, and are not going to be able to get optimum settings on both. Mostly, caster is going to suffer so you have proper camber. Unfortunately this is just how these cars were designed. In the '60s the emphasis was on easy steering, not straight tracking. 0 degrees of caster, or negative caster was not seen as a bad thing. Today road feel is important, and every car has power steering, so a lot of caster isn't a problem from the standpoint of increased steering effort. Modern cars run at least 3 degrees of positive caster, and many run 5 or more.
The Shelby drop helps caster by moving the UCA rearward by about 1/8" as well as lowering it by 1". The 1/8" rearward move adds about 2 degrees of positive caster because you are changing the angle of spindle inclination directly. If the strut rods are non-adjustable further caster adjustment would then need to be made with shims, and you are in a better place than stock, but still back to the dance between caster and camber. Adjustable strut rods allow you to further change the angle of spindle inclination by moving the LCA forward. This will get you another 1.5-2 degrees of positive caster, and allow you to hit 3.5 degrees positive without the need to shim the UCA at all.
Once the caster is set, and I would advise doing that without any shims on the UCA. You then can set the camber by shimming the UCA as needed. The goal is 0-0.5 degrees negative camber (assuming the Shelby/Arning drop), which shouldn't require much shimming and you should be able to shim the UCA evenly. Without the drop you want more like 1.5 degrees negative. More would be better, but will place the balljoints near bind, wearing them out quickly and creating a dangerous situation.
As far as how many shims or their thickness, no real way to tell. These cars were built with tremendous tolerance variation. Even new that question wouldn't get a reliable answer. Add 50 years of wear and tear, wrecks, backyard "mechanic" work, etc. and its even worse. The adjustments exist mostly to correct for these things. The idea of a performance alignment wasn't really even on Ford's radar, which is why there is so little adjustment in the stock system.
The issue with lowering springs is that they lower the front of the car by pulling the suspension up into the body. In so doing you change the static angle of the UCA, shorten its effectvie static length, and the top of the tire tilts inward (negative camber), which is good from a performance standpoint; to a point. A 1" drop can likely be corrected with shims and get you back to an acceptable degree of negative camber. The thing to remember is that you must not run more than 1.5 degrees of negative camber or you will start binding the ball joints and wearing them out. People sometimes talk about Shelby having run more than that on his race cars, but they forget two things. One, these were race cars. Parts only needed to last one race. Two, they put the ball joints in a mill and relived the areas that would bind. This work was hidden by the dust boot so the tech inspectors were none the wiser and the parts were consdiered "stock". This also weakened the ball joints to a degree, and shouldn't be used on the street.
The Shelby drop has two benefits. First, you are lowering the front of the car by dropping the body down onto the suspension. Now, this to a lesser degree still induces stzatic negative camber, because you are lowering the rear of the UCA and changing its static angle, and in effect shortening its length at static ride heihgt, which is going to tilt the tire inward at the top, BUT its not to the same degree as a lowering spring because the 1" UCA drop isn't the same as a 1" shorter spring. The stock configuration is a right triangle formed by the shock tower, the spring, and the UCA from its mounting point on the shock tower to the spring. Both a lowering spring and the Shelby/Arning drop change the triangle from right to scalene (three different angles, none of them a right angle). The difference is in the way they effect that change. The lowering spring removes length from what was the hypotenuse of the right triangle, whereas the Shelby/Arning drop adds length to what was the long leg of the right triangle. Shortening the longest side has more of an impact than lengthening the second longest side. So the Shelby/Arning drop lowers the front end less, but also doesn't induce as much negative camber.
AND, that's not the whole story, but only a snippet. Suspensions don't exist in a vacuum with no movement. Where the Shelby/Arning drop really outshines the shorter spring is when the suspension starts to compress as in cornering. The shorter spring has made the front end sit lower, but its still tied to the stock suspension geometry, which under compression has a lot of camber gain. That is, the tire tends to start tilting outwards at the top when the suspension compresses, so your static setting of say 1 degree negative quickly becomes 0, and then starts going positive. What camber is really measuring is the contact patch of the tire on the road. Obviously the bigger the patch the better the handling. The goal is to have 0 camber under compression in a corner. In a suspension that gains camber you set it with some static negative camber so that under compression it gets to zero. With the stock setup you simply cannot dial in enough static negative camber to do this. It gains too much camber under compression and there isn't enough adjustment. What the Shelby/Arning drop really does is change the rate of camber gain in the suspension, making it gain FAR less camber under compression. This requires a static setting that is both obtainable and not so far negative that it wears the outside edges off the front tires.
The difference in operation is quite noticeable. I've run my car both ways. I got acceptable handling from maxing caster and going to 1.5 degrees of negative camber on stock geometry. The handling with the Shelby/Arning drop and only 0.5 degrees of negative camber is substantially better. Its without doubt the best change you can make to the suspension of your car.
As far as alignment goes, I would advise just learning to do it yourself. I bought some turntables and the Fastrax system for about $300. Alignments typically cost $90 here, so in a couple of alignments on my fleet of vehicles I paid for the setup. I also know I have the specs I want, and can easily change parts now without worry about tire wear or a trip to an alignment shop because I can just do it in my garage.
Last edited by TKOPerformance (7/08/2019 4:57 AM)
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