Axle Movement and Steering Geometry

[David]

'lo,

A couple of question... this is all for a solid xle, leaf sprung front end.

1) First of all, can anyone explain in simple terms what the hell Ackerman (sp?) is? I could never figure it out.

2) When you lift a vehicle, you reduce castor. I have heard that you can add shims to add more positive castor/return castor to normal. Where do you put these shims? (Wouldn't make to sense to put them on the spring perches as that would change yer pinion angle)

3) This is the most important one. If I move my axle forward, all other things being equal (i.e. same size, mounting location for all steering components) what will this do to my steering geometry? Obviously camber and toe would not change, but I assume castor would. Any other comments on how this would affect the steering of the vehicle?

David

PS
I don't think this is uber tech but my last post got moved here so I'm going with the flow =)

[lars]

Originally posted by David
'lo,

A couple of question... this is all for a solid xle, leaf sprung front end.

1) First of all, can anyone explain in simple terms what the hell Ackerman (sp?) is? I could never figure it out.

2) When you lift a vehicle, you reduce castor. I have heard that you can add shims to add more positive castor/return castor to normal. Where do you put these shims? (Wouldn't make to sense to put them on the spring perches as that would change yer pinion angle)

3) This is the most important one. If I move my axle forward, all other things being equal (i.e. same size, mounting location for all steering components) what will this do to my steering geometry? Obviously camber and toe would not change, but I assume castor would. Any other comments on how this would affect the steering of the vehicle?


1. David, do a search of this message board for "ackerman" and you will find your answer.
2. The only place you can put shims is on spring perches. And yes, it will affect the pinion angle as well. If you don't want that to happen, you'll need to cut and rotate your knuckle yokes. You can buy some yoke inserts that provide up to 2 deg of caster adjustment, though.
3. Nothing would change except that you will get a little more side to side range for your pitman arm, since the pitman arm would be closer to the axle.

...lars

[chris siebert]

One thing to watch in moving the axle ahead would be possible interference between the pitman arm and tierod. This may only be an issue with highsteer setup, but could be with a dropped pitman arm as well.