If caster is set with the front crossmember and no spring is used but instead coilovers, and a panhard bar is used in place of spring to control lateral move. How is caster set?
It is set during the build process, with ride angle and height figured in. Minor adjustments can be made when finished.
No matter what type of springs an shocks,you'll still need 6 to 7* of caster on under 2500lbs,an a little less on car that are more lbs. so 5 to 6*caster.
Assuming that you are removing a cross spring and installing coil-overs, there must be some kind of hair pin, four bar or split wishbones locating the axle. With luck you will have enough adjustment to get the correct caster. With split wishbones you will have to raise or lower the wishbone-to-frame mounting point, if it's too low you may have to pie-cut the wishbone near the axle, adjust and reweld it. With hairpins or 4 bar be careful that you have enough thread engagement on the adjusters when you are done. All of this is best done by a competent chassis guy.
^^^^ Yes, caster is set by wishbones, 4-bar, or hairpins (tube wishbones). As far as thread engagement on rod ends, I've always gone with a minimum of 1.5 X diameter of the rod end as a good rule of thumb (ie: 3/4" rod end, minimum 1 1/8" threaded in). Lynn
It is a common misconception that caster is set by the crossmember. It is not. The spring pad on the crossmember needs to be perpendicular to the swing of the arc of suspension movement, not to the caster angle. That angle is required to minimize attempting to flex the leaf spring the "wrong" way, as in bending it fore and aft, rather than up and down. Getting this angle wrong is the reason why so many people think that hot rods are supposed to ride like crap. Caster, as others have correctly mentioned, is set by the relationship between the suspension link, or links, and the axle itself. If you have links, you set caster by changing the length of the links. If you have wishbones, it's much the same. If you have a set of split original, or original style split bones, you set caster by pie-cutting, and welding up the bones, or altering their mounting point on the frame end.
You only modify a crossmember for increased caster to compensate for the increased caster that we as hot rodders tend to like to help the rods track at speed. The reason is spring bind if you don't. Bchctybob nailed it and Lake-Harley gave great explanations on setting the caster. One thing, coil overs usually go hand in hand with a tube axle and split bones don't work the best with tube axles. If you have a tube axle that is.
Thanks so much guys, it makes sense. The front crossmember is degrees to match to swing of suspension travel to prevent bind. More sense that caster is set to the bones.
In your original post, you mentioned "no spring is used, instead coil-overs" , the front crossmember doesn't have any relationship to caster. If you are using bones, set the chassis height, check the caster, correct the caster by wedge cutting and welding the bones. Mount coil-overs last.
Re: The amount of caster needed When I built my '33 Willys coupe (2350# with me in it) I set it up with 10 degrees of caster. THAT WAS TOO MUCH. It gave me wheel shimmy ("death wobble"). I backed off on the heim ends to end up with 7 degrees - the most adjustment I could do - and added a Fiero steering damper. Now it steers, drives, and tracks great. https://www.fierostore.com/Product/Detail.aspx?s=58026&d=324&p=1
I’m getting ready soon to weld in my flat crossmember( no spring pad, maybe some tilt to prevent spring bind, but how much). My car is set at ride height. The bones I’m looking to buy have 10* caster built it. To adjust that shorten the hiems? I’m using trans spring, bones, 4” I beam.
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