Proportioning Valve Test?

[Robert Phillips <r3rfp@dax.cc.uakron.edu>]

This concerns the rear "proportioning valve" on the axle of my 87 4000S:

I was wondering how one would know if the brake proportioning valve is 
working properly.  I have no weird handling/braking traits, but when I 
try to cycle the valve by hand, it seems to be rusted shut/open.  There 
doesn't seem to be any movement of the piston shaft of the valve at all.  
I am assuming that the valve is rusted due to Ohio salt that it has been 
bathed in for 8 years.  How can it be checked with "normal hand tools"?  

By normal hand tools I mean:

Not the pressure gauges in the Bentley manual or any tool 
that would be used by the cast of Star Trek.  

I have the assortment of required metric wrenches and a reasonable amount of knowledge concerning 
the brake system, including fundamental knowledge of the system used on 
my 4000S, but don't know how to "test" this part. 

 I have an 84 4000S that I acquired as a parts car, and would possibly be able to salvage the 
valve off it if need be.
				Thanks
			---Bob