My 1964 C-60 has the second line coming back to the master cylinder. It is my understanding this is a return from the hydrovac.
That it is. In direct words from the books, "the function of which is to compensate for for any loss of fluid from the Multi-Vac hydraulic cylinder."
It also means you have the optional factory brake upgrade with 12.75" hydrovac unit and the larger 1.25" single bore master. The hydrovac can still be sourced, but no luck on even a rebuild kit for the master. (Part # 5462223). It would appear that once worn out, you have to convert to a different setup unless you are lucky enough to track down a NOS master, which are around but very hard to find.
