Servicing the Bendix Hydrovac

The Hydrovac —Second Series

The second series Hydrovac is similar to the first series Hydrovac, in that it consists of a double (or single) piston vacuum suspended power cylinder, a hydraulic slave cylinder and a hydraulic control valve, see Figs, 29, 30, 31, 32 and 33. These fundamental parts are assembled so as to form a single compact unit. The unit is to be so mounted that the major axis of the unit will be as nearly horizontal as possible, with bleed screws pointing up. Exception: There is one Hydrovac assembly (part number 373100, Ordnance number D-72385) which is designed to be installed in an almost vertical position with the hydraulic slave cylinder at the top. Bleed screw locations have been revised in this assembly so that the hydraulic system can be bled and filled with the axis of the hydrovac practically vertical.

The hydraulic connections to the power unit are from the vehicle master cylinder outlet to the hydraulic inlet in the slave cylinder housing, Fig. 35. (See page 32,33 “Double Hydraulic Line System”, for description of Hydrovac units which utilize two hydraulic lines between master cylinder and Hydrovac). The hydraulic line from the end of slave cylinder, always leads to the wheel cylinders.

Vacuum to the power cylinder is provided by connecting a vacuum hose or line to the threaded port hole in the center section between the two cylinder shells, then leading this line to a reserve tank (if used) then to a check valve (required) and from there to a vacuum source, either manifold or vacuum pump. The air inlet in the hydraulic operating valve, is then piped to the air cleaner.

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