GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Chevrolet C-Series Medium Duty Truck B7 🢒 Transmission/Transaxle 🢒 Automatic Transmission - Allison 🢒 Vacuum Modulator Inspection

Notice
    • Prior to making any checks or adjustments to the modulator, check the following conditions:
       - Check the engine performance. Refer to the engine manufacturer service manual.
       - Check the adjustment of the accelerator linkage. Refer to Engine Mechanical for diesel engines only.
    • Diesel engines use a mechanically operated modulator valve in order to aid in transmission shifts. Adjust the modulator cables as needed. Refer to Transmission Modulator Cable Adjustment .
    • Gasoline engines use a vacuum modulator valve in order to aid transmission shifts. Check the vacuum modulator for proper operation. Refer to Transmission Modulator Cable Adjustment .

    Object Number: 201539 Size: SH
  1. Inspect the vacuum modulator hose and the vacuum hose for transmission oil.
    2. • If oil is present, replace the modulator. Refer to Transmission Modulator Replacement .
    • Gas or water vapor in the vacuum hose and the modulator is expected and does not interfere with the normal operation of the modulator.
  2. Inspect the vacuum modulator hose and vacuum hose connections for vacuum leaks using the following procedure:
    3. 2.1. Apply a solution of soap and water to the modulator hose and vacuum hose connections.
    2.2. With the engine running, check for air bubbles on the following parts:
       • The modulator hose
       • The vacuum hose
       • The vacuum hose connections
    2.3. If air bubbles are present, replace the section of vacuum hose that is leaking.