First Range

First Range





First Range Hydraulic Schematic

When the selector lever is moved from N (Neutral) to D (Drive), the transmission shifts from N (Neutral) to first range operation. C, D, and E Solenoids remain energized. Trim Solenoid A and F Trim Solenoid remain de-energized

Shift Valves C, D and E stay in the down position. With normally closed A Trim Solenoid de-energized, Trim Valve A continues to supply full trim pressure through Shift Valve D to C5 clutch, keeping the clutch applied. During the shift, B Trim Solenoid energizes, blocking the exhaust of the B trim signal pressure, causing the pressure to rise. The B trim signal pressure pushes the B Trim Valve down, opening the B Trim Pressure Port to Main pressure. The B Trim Pressure is directed through Shift Valve C, Shift Valve E and the Manual Selector Valve to C1 clutch, applying the C1 clutch. The TCM provides current to B Trim Solenoid, which controls the rate of pressure buildup of the C1 clutch, assuring a smooth transition to first range. The combination of C1 and C5 clutch application produces first range operation.

After the shift to first range is complete, E Solenoid is de-energized followed closely by C Solenoid (timed to prevent E from becoming "latched" down), allowing both valves to move up. B Solenoid is also de-energized, exhausting B trim signal pressure, allowing the B Trim Valve to move up which exhausts B trim pressure. In its up position, Shift Valve E routes main pressure to the Manual Selector Valve which directs the main pressure to C1 clutch, keeping C1 clutch applied. With C1 and C5 clutches applied, the transmission stays in first range.

Control main pressure exhaust for the D pressure switch is blocked by Shift Valve D, keeping the switch turned on and providing feedback to the TCM that Shift Valve D is stroked. With Shift Valve C in its upward position, the pressure feed to switch C is eliminated and with the pressure exhausted, the pressure switch turns off, providing feedback that Shift Valve C is in the up position. With Shift Valve E in its upward position, the control main pressure to the E pressure switch is exhausted and pressure switch E turns off, providing feedback that Shift Valve E is in the up position.

If electrical power is interrupted with the transmission in first range, D Solenoid is de-energized. Normally closed A Trim Solenoid continues to block the exhaust of the A trim signal pressure (signal pressure remains control main) which results in maximum A Trim pressure being maintained. The A trim pressure continues to be directed to Shift Valve D, which stays down due to the "latching" effect of pressure on two different diameter lands and fluid continues to be directed to C5 clutch, keeping C5 clutch applied. Main pressure continues to be directed through Shift Valve E and Manual Selector Valve to C1 clutch, keeping C1 clutch applied. The combination of C1 and C5 clutch application allows the transmission to stay in first range for limp home capability.

If electrical power is interrupted with the transmission in first range, moving the manual selector valve to N (Neutral) will cut off main pressure to C1 clutch and the clutch will be exhausted. C5 clutch remains applied. Because only one clutch is applied, the transmission goes to N (Neutral).

If electrical power is interrupted with the transmission in first range, moving the manual selector valve to R (Reverse) will cut off main pressure to C1 clutch, exhausting C1 clutch. The manual selector valve directs main pressure through the F Trim Valve to the bottom of Shift Valve D, stroking the valve up and opening the path for main pressure to feed C5 clutch, keeping the clutch applied. A trim pressure is then directed to C3 clutch, applying the clutch. The combination of C3 and C5 clutch application produces R (Reverse) range operation. for limp home capability.

Important: If the selector is put back in forward after R (Reverse) has been attained, the selector valve will direct fluid to C1 clutch and Shift Valve D will stay up, directing fluid to C3 clutch, resulting in third range operation.

If electrical power is interrupted with the transmission in first range, resulting in only first, N (Neutral) and R (Reverse) operation, the engine may be shut down and restarted to attain N (Neutral), third and R (Reverse) operation.