Specifications

FRONT:
Coil springs sometimes break near the end and wedge in place without obvious indication of the
failure. Look hard. If you think this might have happened, the only way to prove it is to remove
the spring.
In the front, the measurement is checked on each side between the lower control arm rubber
bumper bracket and cross member flange. This measurement must be perpendicular to the cross
member flange. It is from “iron to iron”. The rubber bumper is ignored. Look at the illustration
below.
Key here is that both sides of the front axle should be the same, and this measurement is used in
the CASTER determination. The front air bags should be inflated to the recommended pressure
for your chassis. Don't attempt to raise or lower the chassis measurements using the air bags. (If
your motorhome has air bags that have been added to the rear to compensate for sagging
springs, make sure they are set to the pressure you plan on maintaining in them.)
Now, take that front measurement and find it in the top row of the chart below, then go down
to the “MOTOR HOME” row to get the degree setting. This is the initial point for the
CASTER setting. This chart is from the 1995 “Chevrolet Motor Home Chassis Service Guide”
for the P Chassis.
Note the various vehicles in the first column that use the P Chassis. Also note that there is a
separate line for the MOTOR HOME version. It is different from the “P-20, 30” line. There is a
distinct possibility that an alignment shop will use the incorrect numbers if you tell them to align
“my P30 chassis”. But of course, we intend to TELL them the CASTER angle we want – once
we go through this entire process.
INCHES 1 1/2 1 3/4 2 2 1/4 2 1/2 2 3/4 3 3 1/4 3 1/2 3 3/4 4 4 1/4 4 1/2 4 3/4 5
G-10, 20 3 1/2° 3 1/4° 3° 3° 2 3/4° 2 1/2° 2 1/4° 2° 2° 1 3/4° 1 1/2°
http://users.sisna.com/cebula/P-Chassis-AlignmentProcess.pdf 18 Version 0.7 –Sep 14, 2005