I know there was a change in standard Caster angle about the time when roads were going from dirt to pavement (late 30's early 40's) and with it came higher average speeds and therefore the need to switch to positive caster angles. And as this car is seemingly untouched (and mostly undriven), I'm taking all four springs off to clean and inspect everything. Once I pulled the front springs I found that the front wedges are thick in the front ergo tilting the axle forward. I haven't actually checked the caster angle but every indication suggests that the car is still running with negative caster. So.... having said all that, and acknowledging that I will most likely be running well above parade speed, I'm assuming upping to a positive caster (removing the wedges) is probably the way to go.
Does anyone have a good argument (or experience) one way or the other.
I was under the impression that positive caster is the condition when the king pin is tilted so the top is to the rear (backwards tilt) when viewed from the side. That is the condition shown on page 45 of the 1937 Chevy shop manual. Positive caster gives steering stability.
I also was under the impression that a wedge between the spring and axle that is thicker in the front increases positive caster. It “rolls” the axle to the rear.
I agree that I would not change anything with having measurements.
Yes you are right about positive caster sloping the top of the king pin towards the rear of the car.
Yes that gives stability to the steering.
But... if the wide end of the wedge is to the front, it will push the front of the spring saddle down, thus rolling the top of the axle and king pin "forward", reducing positive caster or even giving negative caster if carried far enough.
As we both know, the wedges are there to adjust or correct the caster if necessary and may be configured differently form car to car. And we both agree that no assumptions should be made on what Skidplate's caster is presently based on what wedges are there. And so we come to the same recommendation... Measure first! 🙂 👍
. There's an old saying, "Do it right, Do it once." . After you rebuild the steering box and king pins and AFTER you re-arch the leaf springs, the photos describe how to set the alignment. I would suggest setting to factory specs. If it doesn't track well, increase the caster. If it's hard to steer, decrease the caster. Zero caster, toe in, king pin inclination, and/or camber produces shimmy. . . When you apply the brakes, your axle twists top forward, changing your caster. Most alignment shops don't know what a caster shim is. They will tweedle with toe in causing excessive tire wear. Don't go there. But, they can tell you what their machine says your numbers are and you can adjust from there, . . Lou .
Thank you for catching my error. I agree that with the thicker part of the wedge forward on a '37 it will "roll" the axle forward and reduce positive caster.
I have been looking at too many different vehicles lately. I forgot that the front axle is mounted below the springs on a '37 Master.
