Rust Master,Those were great trucks.I worked on them as new when I worked for the Chevy dealer.The brakes sound like it is a Bendix dual hydrovac system.I have the service and overhaul manuals for the 1971 C40-70 that should be the same system as your '72.Send me a PM if you need them.

Wanted Good Woman:
Must be able to cook , clean , sew , tune engines and polish trucks. Must have old Stovebolt and garage. Please send picture of old Stovebolt and garage.