A manual valve (fig. 4-37), operated by the shift mechanism, allows the operator to select park, neutral, reverse, or different drive ranges. A manual valve is basically a multiport spool valve that switches line pressure to selected passages, as it is moved through its operating positions.
The vacuum modulator valve (fig. 4-38) is a diaphragm device that uses engine manifold vacuum to indicate engine load to the shift valve. As engine vacuum (load) rises and falls, it moves the diaphragm inside the modulator. This, in turn, moves the rod and hydraulic valve to change throttle control pressure in
Figure 4-37. - Manual valve operation.Continue Reading