Unless I am mistaken, that is a HydroVac booster setup for Airstream's mid-to-late-1970s HydroVac disc brake setup.
Kevin
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Kevin D. Allen WBCCI (Lifetime Member)/VAC/PrideStreamers/Wisconsin-UP Unit (Primary)/Missouri Greater Ozark Unit (Affiliate Member) #7864 AIR #827
1964 Overlander International
1978 Argosy Minuet 6.0 Metre
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