GM Full-Size Trucks 1980-1987 Repair Guide

Vacuum Pump

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Since the air crossover and intake manifold in a diesel engine is unrestricted (unlike a gasoline engine which has throttle plates creating a venturi effect) there is no vacuum source. To provide vacuum, a vacuum pump is mounted in the location occupied by the distributor in a gasoline engine. This pump supplies vacuum for the EGR valve system, air conditioning servos, the cruise control servos, and the transmission vacuum modulator, where required.

The pump is a diaphragm type pump which needs no maintenance. It is driven by a drive gear on its lower end which meshes with gear teeth on the end of the engine camshaft.

REMOVAL & INSTALLATION



  1. Remove the air cleaner.
  2.  
  3. Remove the vacuum hose from the pump outlet.
  4.  
  5. Remove the air cleaner, and cover the intake manifold.
  6.  
  7. Remove the vacuum pump clamp and bolt and then remove the pump.
  8.  

To install:
  1. Install a new gasket.
  2.  
  3. Install the pump assembly making sure that the drive gear meshes with camshaft gear.
  4.  
  5. Rotate the pump so the inlet tube faces the front of the engine. The pump should be on a 20 degree angle.
  6.  
  7. Tighten bolt and bracket to 20 ft. lbs.(27 Nm).
  8.  
  9. Connect the vacuum hose to the pump outlet.
  10.  
  11. Install the air cleaner.
  12.  

 
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