The vacuum pump (Figure 2-37) is required because the diesel engine does not develop vacuum in the unrestricted air intake manifold.
Since the air crossover and intake manifold are unrestricted, no vacuum source is available as found in gasoline engines. To provide vacuum, a vacuum pump is mounted in the location occupied by the distributor in the gasoline engine. This vacuum pump supplies the air conditioning sen/os, cruise control servo, and transmission vacuum modulator where required.
It is a diaphragm pump which needs no periodic maintenance. It is driven by a cam inside the drive assembly to which it mounts. The pump’s diaphragm moves back and forth causing air to flow into the inlet tube, through the pump, and exhaust out the rear port. The drive housing assembly has a drive gear on the lower end which meshes with the camshaft gear in the engine. This drive gear causes the cam in the drive housing to rotate. The drive gear also powers the engine oil lubricating pump.
Figure 2-38 illustrates the vacuum pump in sectional view. Lubrication of the vacuum pump is via a passage from the rear of the right lifter oil gallery.
See Figure 2-39 for removal and installation of the assembly and Figure 2-40 for general diagnosis.
