Once and for All...Caster Angle

[popeyet]

So I have been investigating all the front suspension specs of my newly rebuilt front end.

Camber is built into the spindles. Not too much to do here except note that the 26-27 spindles have a bit less.

Caster is set by the angle of the wishbone studs into the axle perches. The perches have an angle built into them to lay the axle back. The angle seems to be about 6 degrees in the perches. The wishbone lays theoretically "flat" in a stock setup from the ball to the studs, so by just the math the caster would be about 6 degrees without any other influences.

When I bought my car the wishbone had 2-3 degrees of bend of the studs. When I rebuilt the assembly I wanted to set up at "stock" so I bent back to zero. I assembled everything with new bushings and attempted to measure to see where I was at. The Ford service manual says it is to be 5 1/2 degrees. As we all know it also gives a measurement between spindle bushings. This is a pretty difficult measurement to do because the spindle forging is larger than the bushings and it is very crude the way they describe. Also, as has been discussed, the trig on the angle described matches up more at 3 1/2 degrees more than 5 1/2...so it seems wrong.

I decided to make an inspection tool: and my results surprised me at 3 degrees.

An old timer T guy described to me that when the caster is correctly set is tracks straight and it helps even out the tire wear from outside to inside by making the tire hug the road a little flatter, especially in while cornering.

I really want to get this right! I know I can lay the angle of the wishbone studs to get more caster. Did the previous owner have it right?... I will be installing new wire wheels and tires this winter and want the car to ride the best it can.

DOES ANYONE HAVE THE TRUE AND FINAL ANSWER TO THE 5 1/2 DEGREE QUESTION? Please don't turn this thread into a bunch of hogwash of opinions, that has already been done. I want to know if there is a validated answer from the most experienced and knowledgeable T guys. btw, I had my modern car on the alignment rack recently and it had 5 1/2 degrees of caster, in spec with the car's callouts.

Thanks in advance, There are many things to learn about these cars.


Chris.

[RajoRacer]

I use a 90 degree square on a known level floor with the square against the bottom spindle bushing and one should be able to place a #2 wooden pencil against the top bushing.

[Allan]

When you come to alter the 3 degrees caster you have, it is done by using a heavy bar over/around the axle and using it to bend the radius rod in situ. 5.5 degrees is the target. A little more is better than not enough. More will make the steering when in reverse a little more squirrely but less will do the same for forward gears.

Hope this helps.
Allan from down under.

[1923Touring]

This has nothing to do with your question, and perhaps you are not done rebuilding the front end, but please don't forget to peen over your hub bolts.

-Joshua

[TXGOAT2]

I would go for 5 1/2 to 6 deg. caster. I believe that with caster at the high end of the spec range, you'd want to set the toe in to the higher end of the spec range. As noted, caster has a huge effect on how well the car tracks. Caster should be even on both sides, or very close to it. Caster, camber, and toe-in are all related, and all of them need to be in the correct range. Of course, the frame needs to be straight and the motor mounts in good order, and the rear axle and spring needs to be in good order for the car to track and handle as it should. Inadequate or split caster will make the car wander all over the road, no matter how good everything else is.

[Norman Kling]

One thing which will affect the castor is the arch of the front spring. If the radius rod is exactly flat or if the spring brings the front lower or higher than the ball. Even the load on the car will make a difference. So try to get it as close as you can and if the car steers straight and the pitman arm is approximately straight up and down when the wheels are pointing straight ahead it should be fine.
Norm

[TXGOAT2]

Check caster with the car on a level surface, resting on its wheels and fully assembled.

[Art M]

I like Rajoracer's method of measuring caster except my sliderule indicates a .44 inch spacer should be used in order to obtain 5.5 degree caster.

Art Mirtes

[speedytinc]

I like Rajoracer's method of measuring caster except my sliderule indicates a .44 inch spacer should be used in order to obtain 5.5 degree caster.

Art Mirtes

Thats a good dimension. Years ago I did the math & the given ford dimension didnt jive with the given angle.
Anywhere between 3/8 & 1/2" makes the T want to track straight, especially good for hi speed running.

[popeyet]

All good stuff...Thanks Y'all!

Surely going to adjust to the 5 1/2 range. No more confusion.


Chris.

[Allan]

Chris, you need to do something about the six bolts at the hub. Once tightened, these are peined over to stop them coming loose. Yours are a tad too long to pein, so they need to be cut back a bit. A few miles/trips later, the nus should be re-tensioned and the bolts re peined

Allan from down under.

[popeyet]

Allen,

I am aware. As I stated in the first message I am going to wire wheels this winter. I only got the car going this past summer and basically drove around dialing in things. The front end alignment is one thing that I really want to get right. The wheels on the car now wobble quite a bit and at this time they will not be the long term solution.

So thanks for your concern and input. but not to worry.


Chris.