Hi Guys maybe a dumb question but how do i accurately measure the angle on my front axle and front Crossmember ? is there some kind of formula ? I understand the front crossmember needs to be laid back about 7 degrees but I didnt build the chassis and want to check it. have asked several rodders and got completely different view points Model A Roadster on 32 rails, Model A front cross-member, Roadster Supply front axle, multi leaf front spring.
Most smartphones can run an app that will read angles. Place the phone on the chassis and zero it, then place it on a suitable place on the crossmember to read that angle, then repeat the process for the axle. Simples. If you're awkward and don't want to use a smartphone, you can pick up a digital angle measuring device from the likes of Amazon for cheap.
Caster is the angle between a line that's perpendicular to the ground and the front spindles. It should be between 5-10 degrees. You can measure it with a cell phone app or a hardware store angle finder, placed next to your front spindles.
Measuring the angle is easy. You just need to know when. By that I mean you need to have the frame set in a position that included frame rake and tire rake. The 7 degree layback is where you want the axle to wind up. That may, or not, be the crossmember angle depending what crossmember and when it was installed. As example many aftermarket crossmembers come with the center layed back 10 degrees. This is done to make it easier to install into a frame that is sitting level in a jig during fabrication. Then the typical 3 degrees of frame / tire rake reduces the 10 back to 7. Ideally you don't fully weld the crossmember until you have checked it with tires on and enough simulated weight on the springs. If the car is assembled you can adjust the caster by pie cutting the bones or adjusting hairpins / four link or their attachment points.
Caster angle is relative to a line perpendicular to the ground, isn't it? It has nothing to do with the chassis. Once you have your chassis set where it will ride, the cross member needs to be set so the caster angle will be correct in relation to absolute vertical.
Yes - 7 degrees is the recommended caster angle. (My sedan has 10 degrees and I have read on here of some having 5 degrees). although this may cause the spring to move or bind.
Of course my bad, I meant more the crossmember in relation to the chassis. But obviously the better way is to set everything at ride height with full weight then measure from a smooth flat floor.
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