[BusNit]

There is a pressure regulator for the transmission modulator. The modulator itself is a wear item and needs to be replaced at each transmission oil change. Mine was bad and leaking air into the trans fluid. I could hear the gurgling when the coach sat. Pressure I believe is set to 60psi.

To find the line follow the air hose from the transmission modulator (right side) and see which regulator it goes to. There are two pressure regulators on the passenger side engine wall. One is for the tag axle (25-30psi setting) and the other is for the modulator.