On my '59 Canadian GMC 9600, the check valve was on the firewall immediately below the voltage regulator, and there was a 3/8" hose connecting it to the engine intake manifold. It is a brass casting about 2 inches square.
Mine actually contained two check valves in one casting - one supplied the two-speed axle circuit while the other supplied the hydrovac.
It might be worth taking the check valve apart and cleaning it - old oil might gum up the springs and affect how much vacuum it supplies.
Last edited by Puffie40; 12/31/2024 7:21 AM.
