• If electrical power is interrupted with the transmission is in fifth range, (fifth range converter operation) and the Manual Selector Valve is moved to reverse, C2 clutch exhausts through the Manual Selector Valve, releasing the clutch. C3 clutch remains applied. With only one clutch applied, the transmission goes to neutral. • If electrical power is interrupted with the transmission is in fifth range, resulting in only fifth and neutral operation, the engine may be shut down and restarted to attain neutral, third and reverse operation (reference Section A— Neutral).
H. Hydraulic Circuit—Reverse (Foldout 11) • When the Manual Selector Valve is moved from neutral to reverse and the throttle setting is above closed throttle, C, D, and E Shift Solenoids remain energized, A Solenoid remains de-energized, supplying A Trim pressure through Shift Valve D, to the C5 clutch, keeping the C5 clutch applied. B Solenoid remains de-energized, keeping B Trim pressure exhausted. With only C5 clutch applied, the transmission remains in neutral. Reverse signal pressure is exhausted, removing pressure from the reverse pressure switch, turning on the normally closed reverse pressure switch. When the Manual Selector Valve is moved from neutral to reverse and the TCM determines that the engine is at closed throttle, B Trim Solenoid energizes, which acts on the Trim Valve B gain valve because reverse signal pressure no longer pushes the valve up. The gain valve pushes the B Trim Valve down, raising B Trim pressure. B Trim pressure is directed through Shift Valves C and E, the Manual Selector Valve, the TCC Valve to Shift Valve D, stroking the valve up (even though D Solenoid stays energized). With Shift Valve D up, pressure from Trim Valve B passes through Shift Valves C and E, through the Manual Selector Valve, the TCC Valve, and Shift Valve D to the C5 clutch, keeping the clutch applied. Pressure from
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Copyright © 2004 General Motors Corp.
Trim Valve A, which was applying the C5 clutch through Shift Valve D, is directed through Shift Valve D to the C3 Clutch. • The TCM temporarily energizes A Solenoid to control the rate at which Trim Valve A supplies pressure to the oncoming C3 clutch, assuring a smooth transition to reverse. When A Solenoid energizes, A Trim signal pressure is exhausted. As A Solenoid is de-energized, A Trim signal pressure increases. Initially, the Trim Valve A gain valve spring keeps the gain valve away from Trim Valve A, so only the A trim signal pressure acts on Trim Valve A. As the A Trim signal pressure increases, the A Trim pressure increases. The A Trim signal pressure also acts on the gain valve, forcing the valve down and compressing the gain valve spring. When the gain valve spring is compressed sufficiently, the gain valve contacts Trim Valve A. The gain valve spring allows the C3 clutch initial apply to be controlled at a lower gain rate, improving control of the oncoming C3 clutch. Once the gain valve makes contact with Trim Valve A, A Trim pressure increases at a higher gain rate. When the shift to reverse is complete, A Solenoid fully de-energizes and Trim Valve A supplies full trim pressure to the C3 clutch. B Solenoid remains fully energized and B Trim valve supplies full trim pressure to the C5 clutch. • The application of C3 and C5 produces reverse range operation. • Even though Shift Valve D moves up due to B Trim pressure, B Trim pressure acts on Pressure Switch D, keeping Pressure Switch D on. Shift Valve C remains stroked down, directing control main pressure through Shift Valve C to Pressure Switch C, keeping the switch on. Shift Valve E remains stroked down blocking the exhaust path for control main pressure being supplied through an orifice to Pressure Switch E; the pressure keeps Pressure Switch E on. With reverse signal pressure exhausted the normally closed Reverse Pressure Switch is on, providing
1000 and 2000 Product Families Principles of Operation—December, 2004
