Now tag axle pressure

[Glenn Allen]

Repost with the correct subject....sorry

Scott,

I believe this is the way the rear air works for ride height, but I'm
sure someone on here can correct any mis-conceptions I have:

There are two ride height control valves in the rear that controls
the rear frame height by controlling the pressure to the drive axle
air bags. You can adjust the control height rod to change the height
of the rear, but this only affects the drive axle air bags. This
must be done on a level surface, and there are specs for the actual
height that should be measured when adjusting.

The tag axle air bag pressure is controlled by a pressure reducing
valve located on a cross member just behind the tag axle. This is an
adjustable valve. Conceptually, the tag axle should not be used to
control ride height, but should be used for load distribution. As
you increase pressure on the tag, the load will be removed from the
drive axle and shared by the front and tag axles. Too much pressure
in the tag can cause too much load on the front axle. Too little
pressure on the tag, can cause wheel lock-up during agressive braking
and also possibly overload the drive axle. So, depending on your
load distribution, the required tag air pressure will vary from coach
to coach.

The pneumatic diagram for my coach recommends a 40psi setting for my
tag. I think this is too little based on braking tests. I believe
45 to 50 psi seems to be better for me. I will be weighing the coach
soon and making final adjustments based on axle weight distribution.

I replaced my leaking Tag pressure reducing valve with one I ordered
from NAPA (they ordered from Bendix). My docs call for the RV-1
279926 40 psi. I ordered the RV-1 278247 50 psi version. They are
both adjustable so either one will work. NAPA has some "cloans", but
I don't recommend using them because the ports are arranged
differently and will require a plumbing change.

So, hopefully, I have all of this correct.

Glenn Allen
1986 PT-40
Marietta, GA