What I ment by 'preload' was to spread the spring ends a inch or so and then attach the shackles flat. I've always had to do that on front and rear cross springs to get them to end up with the right shackle angle (about 45 degrees). I usually fab up a screw jack thing with some tubeing and a threaded rod, and spread the ends. Any time I've attached them without the preload-- the shackles hang straight down under load.
I've seen rear high arch springs that the shackles hang straight down, that work, but they need a panhard bar to hold the side movement, where if you have the shackles at a 45 or so--that holds the rear from swaying back and forth too much. Same for a front end--I don't have a tracking bar on my front axle on my 26 and it has a 45 on the shackles.
Panhard bars are probably better, no matter what though.
Just engineer it as you go along--even 'wrong' stuff works--often pretty good--like ackerman -- I've never built a car with the 'right' ackerman and I ain't dead yet
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Ts are great-- If a guy could only have 1 hotrod--it oughtta be a T.
PA41