Specifications

(You can make up the measuring tool by picking up a cheap plastic protractor, file a small notch
at the 0 center on the flat side. Then capture a knotted string in that notch with a weight at the
end of the string hanging down to indicate the degree of angle - not rocket science. Of course, if
your eyesight is as bad as mine, get a big protractor.) Also, note that early versions of the P
Chassis Service Manual had the words 'added' and 'subtracted' in a & b above reversed and c &
d above reversed.
As an example, let's assume you previously measured front ride height on both sides as 4 1/2”.
The table says the CASTER should be set to 3 ¼ degrees. But, you then measured the frame
angle and found an up-in-rear angle of 3 degrees. (b) above says you need to add that figure and
you wind up with a setting of 6 ¼ degrees. That's the figure you should tell the alignment shop
to use for CASTER – in this example.
If you should measure the frame angle on both sides of the motorhome and come up with one
side positive angle and one side negative angle, stop and get some help. But, this would be
rather extreme.
Two more settings to go for the alignment: CAMBER and TOE-IN.
Here's the table from the same 1995 manual. Note that there is no line for “P-20, 30.”
Interesting.
http://users.sisna.com/cebula/P-Chassis-AlignmentProcess.pdf 20 Version 0.7 –Sep 14, 2005