Fourth Range

Fourth Range





Fourth Range Hydraulic Schematic

Before making the shift from third to fourth range, the Transmission Control Module (TCM) makes certain all of the shift valves are in the correct position, with Shift Valve C down and Shift Valves D and E up.

A Trim Solenoid is energized, opening the A trim signal pressure to exhaust which allows the A Trim valve to move up and C3 clutch pressure is exhausted B Trim Solenoid is energized, raising the B trim signal and B Trim pressures. The B trim pressure is directed through Shift Valve C, Shift Valve E, Shift Valve D and the Manual Selector Valve to C2 clutch. applying the clutch. Main pressure continues to flow through Shift Valve E and the Manual Selector Valve to C1 clutch, keeping C1 clutch applied. The TCM supplies current to B Trim Solenoid, which controls the rate at which Trim Valve B supplies pressure to C2 clutch, and current to A Trim Solenoid, which controls the rate at which Trim Valve A exhausts C3 clutch, assuring a smooth transition to fourth range.

The combination of C1 and C2 clutch application produces fourth range operation.

After the shift to fourth range is completed, E Solenoid is energized, directing control main pressure to the top of Shift Valve E, pushing the valve down. In its downward position, main pressure is redirected through Shift Valve D and the Manual Selector Valve to C2 clutch, keeping C2 clutch applied. The flow from the B Trim Valve to Shift Valve E is directed through the Manual Selector Valve to C1 clutch, keeping C1 clutch applied.

Pressure switch E turns on and Pressure switch C remains on, providing feedback that the valves are stroked down. Pressure switch D remains off, providing feedback that Shift Valve D is in its up position.

If electrical power is interrupted with the transmission in fourth range, A, B, and F Trim Solenoids, and Shift Valve Solenoids C and E are de-energized. Shift Valve C moves before Shift Valve E, directing control main pressure to the top of Shift Valve F "latching" it in the down position Main pressure continues to flow through Shift Valves E and C) and the Manual Selector Valve to C2 clutch, keeping C2 clutch applied. When de-energized, the normally open B Trim Solenoid exhausts the B trim signal pressure, allowing the B trim valve to move up and C1 clutch exhausts. After Shift Valve C moves up, the C1 clutch exhausts to exhaust backfill. Normally closed A Trim Solenoid blocks the exhaust of A trim signal pressure, allowing the A trim signal and A Trim Pressures to rise. Trim Valve A directs full trim pressure through Shift Valve D to C3 clutch. applying the clutch. The combination of C2 and C3 clutches applied produces fifth range operation for a limp home capability. If the Torque Converter Clutch (TCC) is applied, de-energizing the F Solenoid causes the F Trim valve to move up, exhausting pressure from the top of the Converter Flow Valve. The Converter Flow Valve moves up, redirecting main overage to converter in and converter out to the cooler. The TCC is now released.

If electrical power is interrupted with the transmission in fourth range (causing fifth range converter operation) and the Manual Selector Valve is moved to N (Neutral), C2 clutch exhausts through the Manual Selector Valve to exhaust backfill, releasing C2 clutch. C3 clutch remains applied. With only one clutch applied, the transmission goes to N (Neutral)

If electrical power is interrupted with the transmission in fourth range (causing fifth range converter operation) and the Manual Selector Valve is moved to R (Reverse), C2 clutch exhausts through the Manual Selector Valve, releasing the clutch. C3 clutch remains applied. With only one crutch applied. the transmission goes to N (Neutral).

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