Airk Brakes won't pressure up

[bluebirdfitz]

I just started up my 1978 Wanderlodge FC31 bus after a long winter
hiatus. It started right up (in a sea of blue smoke), but the air
brakes won't pressure up past sixty. The same thing happened last
year, but it seemed to fix itself when I went back out a week later.
The bus is old, but only has about 30,000 miles on it. Any ideas of
what I should be checking first.

Thanks very much for any help.

John Fitz
78 Bluebird FC 31
Maynard, MA

http:http://www.johnfitz.com