I have it tore down for all new lines, hoses, cylinders, mastery cyl etc. My truck has the usual Hydrovac mounted under the cab it's a double diaphragm unit. The back axle brakes are operated from a second hydrovac unit with a small master cylinder on it with it's on reservoir. I am going to get the main Hydrovac rebuilt or get a rebuilt one. I don't see any listed like the back one when I look online. Did all tandem axle trucks have theses? I don't see it listed in the service manual. It doesn't look it it has seen attention for many years.
