GM: Electra/Park Avenue/Ninety-Eight 1990-1993

Vacuum Modulator

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Fig. Fig. 1 Vacuum modulator and related parts

The vacuum modulator system controls shift feel or harshness by sensing changes in the engine load, indicated by engine vacuum. The modulator accomplishes this by controlling main line pressure boost. The vacuum modulator system may be suspect if your transaxle shifts harshly or slips. To operate properly, the vacuum modulator requires 13-17 in. Hg of engine vacuum at hot engine idle, checked at the modulator while in drive.

REMOVAL & INSTALLATION
  1. Disconnect the negative battery cable.
  2.  
  3. Raise the vehicle and support safely.
  4.  
  5. Remove the vacuum line from the modulator.
  6.  
  7. Remove the bolt and modulator retainer.
  8.  
  9. Carefully pull the modulator out of the case. Discard the O-ring.
  10.  

To install:

  1. Install a new O-ring and lubricate.
  2.  
  3. Install the modulator to the case.
  4.  
  5. Install the retainer and bolt. Torque to 15 ft. lbs. (20 Nm).
  6.  
  7. Connect the vacuum line to the modulator. Check for proper vacuum at the vacuum line.
  8.  
  9. Connect the negative battery cable and road test.
  10.  

 
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