Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot) then the caster is positive; if it's tilted forward then the caster is negative. Conventional steering systems are designed with a positive caster angle to achieve good self-centering of the wheels while driving.
By installing BD's Cam Caster Adjuster Kit on the radius control arms of the Ford 2005-2010 Super Duty pick-ups (Diesel or gas), correcting the caster to a more positive angle is made easier.
The Cam Caster Adjuster kit will help prevent a number of potential steering problems and have your rig driving straight again!