The spring shackle mounts were not in a straight line when measured across the top of the axle between the spindle bolts.
I bent the axle at the center so the four holes (spindles and shackle mounts) are now aligned.
Now the axle is no longer "flat". It has a 3/8" gap between the center (the section held in the vise in the attached image) and the floor if it is laid "front side down". In other words, the center of the axle is 3/8" further back than at the ends when installed in the car.
I assume this means that the axle actually needs to be bent just inboard of the spring perch holes on both sides and not at the center where I have worked it.
Question: Will the "not straight" axle be of much concern as long as the holes are all in alignment?
The holes need to be parallel in both directions, that is front to back and side to side. The center part is merely to hold everything together. You need to assemble things and then check the castor and camber to see how it is affected.
I would imagine at some point in time someone used a chain to pull the car that axle was on and gave it a jerk and pulled the center of the axle out, or it could have been driven into a stump and bent it backwards.
Here's an older post showing how someone else took the bow out of their axle:
The two end holes need to be aligned with each other. In other words: the spindle bolt holes need to be parallel.
The two spring perch holes also need to be in alignment with each other, but not aligned with the king pin holes for the spindle bolts.
Forget the string at the top. Sight the two spindle bolt rods and get them aligned with each other.
The inside holes need to be behind the string in order to give the spindles caster.
Having all four holes parallel will cause driving problems, that's why it is important that the axle not be put in backwards.
Aaron, your post is at odds with what I had always thought. Perhaps I have been under a misapprehension.
I thought all the holes in the axle were in the same plane, and the caster in the axle was a result of the spring perches being off-set. The eye in the perch is at an angle to the shaft which goes through the axle.
Perhaps others can put me straight.
Allan from down under.
I don't think much of anything makes any difference at all.
Allan -- You are correct, all 4 holes in the axle need to be aligned with each other. Aaron is mistaken. The caster is provided by the perches, not the holes in the axle. The axle cannot be put in backwards; the caster is in the perches.
I'm with Allan & Mike.
Ancient history here, but, about 30 years ago, one of our members mounted his perches back to front and because of it, ended up flipping his '18, very nearly totaling it, himself and his lady.
Allen and Mike, you are right.
When taking the bow out of an axle, you can't just bend one place, there may be several.
The string should be around the two end rods so the string is on the out side of all the rods, in the middle. A string over the top of the rods won't tell you a thing to get an axle zeroed.
When all four rods are in a straight line, and the rods measure the same at top and bottom, between the rods, the axle is straight, and can be put in either way, and that is all there is to do with the axle, for straightening.
If you have bad spindle bolt holes, they should be fixed first.
If that is your rods you are showing, they are made wrong, and will not work.
Unless you have cones in the holes on each side of the axle holding the rods straight, you never will be zero.
Yes, I am mistaken.
The offset is in the spring perches,
I knew that, just have not worked on front ends for a while.
I have had to turn the axle around on a couple of cars because
I couldn't get the spring perches out.
No problems flipping the axle if it's needed to get the perches right, just remember to keep the spindles so the RH spindle has LH threads and the LH spindle has RH threads - otherwise the front wheel bearings will tend to tighten up while driving and may destroy the hubs.
I used a bottle jack and two chains; one bolted to each spring perch hole and another from the center of that chain to the leg of the metal work bench to stabilize the bottle jack once the pressure was on.
It worked quite well apart from only being able to bend near the center of the axle. I think mine actually needs to be bent nearer the ends which would get the four holes in alignment without having the center of the axle bent 3/8" rearward.
Here are a couple views while the axle was under pressure from the jack. Ford's steel behaves a little like chewing gum, very ductile.