Cross steering on straight axle.. Steering box angle

[Crosley.In.AZ]

If I understand this:  the steering box pitman arm needs to be perpendicular to the axle?

So the pitman arm swings in a level path left & right  with the axle tube.

Steering box , bolted to the frame rail, with steering pitman arm shaft straight down  ?

[enjenjo]

Not necessarily straight down. Many are angled back at the bottom as much as 15 to 20 degrees. The Pittman arm then describes an arc that is higher on the ends that it is in the middle.

[Crosley.In.AZ]

thought,  I would post up a couple pics for reference.  

This is a Corvair cast iron box I  have for show n tell here. Not the box I would use

Enjenjo:  you are correct on the pitman arm swing.   I have seen both, box straight, & angled slightly.

Angled up slightly would be better for my application I think.


I did not know what problems if any a slight angle would do to the steering  action.

[chimp koose]

If you are running positive caster , tilting the box as you have shown will raise the pitman arm as it swings in its arc side to side . If the tilt as shown was equal and opposite to the caster angle and the pitman arm was close to the same center to center length as the steering arm from king pin to tie rod end , then the steering shaft from pitman arm to the opposite steering arm would likely stay at the same angle (horizontally ) throughout its arc of movement . In theory this might result in consistent movement of the steering system in relation to the amount of steering wheel movement except for the fact that as the wheels turn, the steering arms move closer to the axle centerline(viewed from above) while the pitman arm moves away from axle centerline , creating an angle between them that constantly increases as you turn sharper  . If the pitman arm was tilted at a steeper angle, the steering shaft would not stay at the same angle but the pitman arm would also not swing away from axle centerline as much . Which is better , or is it all that important ? I don't know . I think the angle the steering shaft made in relation to the axle centerline (as viewed from above)would be the one that would change the most so that an effort to reduce it (tilting the box more than the caster )might do more to help steering geometry than trying to keep it at the same angle horizontally . Experts please chime in . I would like to learn too !

[GPster]

If you are running positive caster , tilting the box as you have shown will raise the pitman arm as it swings in its arc side to side . If the tilt as shown was equal and opposite to the caster angle and the pitman arm was close to the same center to center length as the steering arm from king pin to tie rod end , then the steering shaft from pitman arm to the opposite steering arm would likely stay at the same angle (horizontally ) throughout its arc of movement . In theory this might result in consistent movement of the steering system in relation to the amount of steering wheel movement except for the fact that as the wheels turn, the steering arms move closer to the axle centerline(viewed from above) while the pitman arm moves away from axle centerline , creating an angle between them that constantly increases as you turn sharper  . If the pitman arm was tilted at a steeper angle, the steering shaft would not stay at the same angle but the pitman arm would also not swing away from axle centerline as much . Which is better , or is it all that important ? I don't know . I think the angle the steering shaft made in relation to the axle centerline (as viewed from above)would be the one that would change the most so that an effort to reduce it (tilting the box more than the caster )might do more to help steering geometry than trying to keep it at the same angle horizontally . Experts please chime in . I would like to learn too !

That's an excellelent explanation (i don't have a good use of words). One thing I would add is that you need to make sure that when the steering box turning is centered (half way between full left and full right) that an imaginary line of the pittman arm between the steering box splined shaft and the tie rod end hole is 90 degrees to the imaginary line between the spindles. That way straight ahead will be at the center of the pittman arm's arc so that there will be an equal amount of stroke to full left and full right from center. I understand that but that doesn't mean anything. GPster

[Crosley.In.AZ]

Gasser type car build.  A bout 7* of caster in axle.  

I dont want any funny steering business as the car wheelies and carrys the tires for a couple hundred feet or 4 feet, which ever happens

[chimp koose]

Do all you can to eliminate bump steer. Wheelies have a tendency to go bump at the end!