Manual First

Manual First:

MANUAL FIRST

Manual First can be used for maximum engine braking when descending steep grades. Manual First can be selected at any vehicle speed. However, the transmission will downshift into Manual Second and downshift to Manual First when vehicle is at a specified speed according to vehicle application.

^ Manual Valve: In the Manual First range, line pressure from the pressure regulator valve is turned into Drive, D 321, D2-1, and lo fluid pressures. The Drive fluid pressure is directed to the forward clutch, the D321 fluid pressure is directed to the overrun clutch, D2-1 fluid pressure is directed to the 2-3 shift valve, and the lo fluid pressure is directed to the Pressure Switch Manifold (PSM) and rear servo.
^ Pressure Switch Manifold (PSM): Lo fluid pressure from the manual valve is directed to the Lo pressure switch on the PSM, this sends a signal to the Powertrain Control Module (PCM) that the transmission is in manual lo. Drive fluid pressure is also supplied to the PCM as in all other gear ranges but Reverse, Neutral and Park.
^ Solenoid "A": Energized, signal "A" fluid pressure forces the 1-2 and the 3-4 shift valves to the extreme left.
^ Solenoid "B": De-energized, exhausting signal "B" fluid pressure through the solenoid.
^ 1-2 Shift Valve: Held to the extreme left by signal "A" fluid pressure. The actuator feed and drive pressures supplied to the 1-2 shift valve are blocked.
^ 2-3 Shift Valve: Is held to the extreme right by spring pressure and D2-1 fluid pressure from the manual valve as in intermediate (second) gear.
^ 3-4 Shift Valve: Is forced to the extreme left by signal "A" pressure.
^ Rear Servo: Lo fluid pressure from the manual valve is directed to the #7 checkball, (which then becomes Rear Band Apply (RBA) fluid pressure) and into the rear servo which applies the rear band.
^ Forward Clutch: Is applied by Drive fluid pressure from the manual valve.
^ Overrun Clutch: D321 fluid pressure from the manual valve seats the #1 checkball in the case and causes the fluid to flow through an orifice (which becomes overrun fluid pressure) through the case, pump housing and into the overrun clutch housing which applies the overrun clutch. Thus the overdrive roller clutch becomes ineffective and provides vehicle engine compression braking.