The vacuum modulator is used to sense any changes in torque input to the transmission. It then transmits this signal to the pressure regulator which controls line pressure so that all transmission torque requirements are properly met. This helps to keep shifts smooth at all throttle openings.
REMOVAL & INSTALLATION
See Figure 1
- Raise and support the vehicle safely using jackstands.
- Disconnect the vacuum pipe from the transmission.
- Check to see if the driveshaft will interfere with access to the modulator assembly. If so, matchmark and unbolt the shaft from the flange, then reposition and support it aside.
- Use a large-mouthed, but flat-bladed wrench to loosen and remove the vacuum modulator. A special tool No. J-23100 is made for this purpose.
- Test the modulator for wear or damage and replace, if necessary.
- If the old modulator is being reused, be sure to obtain a NEW O-ring and modulator plunger.
- Install the modulator, being careful not to overtighten it.
- Connect the vacuum pipe.
- Remove the jackstands and carefully lower the vehicle.
- Check the transmission fluid and add, as necessary.
See Figure 2
A faulty modulator could cause one or more of the following symptoms:
- Remove the modulator from the transmission.
- Turn the modulator so that the vacuum line stem faces straight downward. If transmission fluid comes out of the modulator stem then the vacuum diaphragm is bad and the unit must be replaced.
Keep in mind that gasoline and/or water vapor may settle in the vacuum side of the modulator and this is OK, unless the vehicle may be exposed to temperatures below 10°F (-12°C), then the modulator must be replaced to prevent operational problems.
- Use a hand-held vacuum pump to check movement of the vacuum plunger. Connect the pump to the vacuum stem and apply 20 in. Hg (500mm Hg) while watching the plunger.