Modulator Assembly: Inspection

1. Inspect vacuum modulator valve for scoring, nicks or burrs.
2. Inspect "O" ring seal for nicks or cuts.
3. Inspect vacuum modulator for bent neck or dented can.
4. Install hand-held vacuum pump to modulator and apply 18 in. hg. (15 kPa).
5. Install Comparison Gauge (J-23738-A) onto modulator and a known good modulator of the same type. See Fig 1 .
6. Apply pressure to both. If indicator line moves out of view, modulator must be replaced.

Fig 1: Testing Modulator

Courtesy of GENERAL MOTORS CORP.