Master Cylinder Vacuum Leak???
72 Chevelle with moreate engine mods to a 454 I just rebuilt. Also, converted rear drums to disks.
Now this one really has me baffled. Due to a lack of vacuum to the booster/brakes I installed an auxillary Summit vac pump. Per the instructions, I ran a vac line from the pump directly to the break booster. When I turned it on there was a vac leak around the master cylinder. Upon further evaluation I was surprised to find at the bottom of the master cylinder just before it bolts to the booster, a through hole which intersects a vertical hole in the master cylinder housing. If I place my fingers over the hole I eliminate the vac leak. The hole looks like it was machined at the factory.
Would anyone know the purpose of this hole and if I can block it up so I have complete vac?
Thank you in advance for any input you may add.