Dana 30 and Dana 44 Front Axle Caster Adjustment

Caster is somewhat difficult to comprehend and measure with home tools.  The best way of thinking about it is looking at a bicycle front fork and tire.  The forks arrive at the center hub at an angle.  The positive caster allows the tire to return to center (the reason you can ride a bike with no hands).  Another example of extreme negative caster is shopping cart front wheels, they will follow in any direction that it is being pushed.  Most Jeeps were equipped with about 4 degrees positive caster with no adjustments.  Adding lift kits can mess with the castor decreasing the angle sometimes to the point of becoming negative.  This will cause the Jeep to wander about the road.  An improper caster angle can make flat towing dangerous and coming out of sharp corners exciting due to the wheel not coming back to center.

Castor Correcting Degree Wedges aka Shims

See:  Installing Caster Adjusting Leaf Spring Wedges aka Shims

Degree wedges are usually the easiest to install and "experiment with".  They also are available in greater degree variations.  Ball joint sleeves are more involved to install but aren't prone to wear and causing noise or causing u-bolts to come loose.

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Caster Correcting Upper Ball Joint Sleeves

See:  Installing Caster Adjusting Upper Ball Joint Sleeves or "Caster Correctors"

Other options

Installing a shackle reversal kit can drastically change the caster in a positive way due to the front shackle mount becoming fixed and the rear mount becoming longer causing the spring angle to change making the caster move in a positive direction.  This option would be for someone with an advanced skill level.

Altering the steering knuckles.  This option involves cutting off the steering knuckle, resetting the caster angle, and re-welding the knuckles to the housing.  This option is usually best left to a professional.