Overdrive Range, First Gear

When the gear selector lever is moved to the Overdrive (D) position from the NEUTRAL (N) position the following changes occur to shift the transmission into Overdrive Range - First Gear.

Manual Valve (404)
Is moved by the gear selector lever and allows line pressure to enter the D4 passage.

Number 6 Ball Check Valve (372)
Located in the control valve body (300), blocks forward servo apply passage forcing D4 pressure to the forward servo boost valve (367), the forward servo feed orifice on the spacer plate (370). When the manual valve (404) is moved from DRIVE to PARK or NEUTRAL, the ball check valve unseats to allow for a quick exhaust of servo apply fluid and release of the forward band assembly (688).

Forward Servo Boost Valve (367)
Opens under high line pressure (high throttle position) allowing D4 fluid to by-pass the feed orifices to enter the servo apply passage. This provides for a quick fill of the servo passage and quick apply of the forward band assembly (690) to prevent slippage during abusive shifts from PARK or NEUTRAL to DRIVE.

Forward Servo Assembly (15-22)
Applies and holds the forward band (688) during all forward gear drive ranges.

Forward Band Assembly (688)
Wraps around and holds the 1-2 support outer race (687) during all forward gear drive ranges.

Transmission Fluid Pressure (TFP) Manual Valve Position Switch
D4 fluid is routed to the TFP manual valve position switch and the TFP manual valve position switch signals the PCM that the transmission is in the Overdrive range.

1-2 Shift Solenoid (SS) Valve (315A)
Energized (ON) by the Powertrain Control Module (PCM), high pressure in the 1-2, 3-4 signal fluid circuit holds the 12 shift valve in the downshifted position. 1-2, 3-4 signal fluid also is routed to the 3-4 shift valve, but is not effective.

2-3 Shift Solenoid (SS) Valve (315B)
Energized (ON) by the Powertrain Control Module (PCM), high pressure in the 2-3 signal fluid circuit holds the 2-3 and 3-4 shift valves in the downshifted position.

Input Clutch
Remains applied from NEUTRAL to DRIVE and becomes effective as the forward band applies. The input sprag holds at this time.

1-2 Support Roller Clutch
The 1-2 support roller clutch holds when the forward band is applied.