a pretty comprehensive explanation and procedure can be found in this
samba thread

http://tinyurl.com/276rk8v

alistair

On 1-Nov-10, at 1:02 PM, Larry Alofs wrote:

Having replaced the rubber bushings on the radius rods on my '91 GL, I
would like to check the castor, since it is affected by the rod
measurement.  The Bentley mentions this and give castor specs, but
does not seem to give any clue about how to actually measure or check
the castor.  Maybe it's there and I just haven't found it.
    Anyone?

Thanks,
Larry A.