D-4 - First Gear

Drive Range - First Gear:

D-4 - FIRST GEAR

OVERDRIVE ROLLER CLUTCH - HOLDING
FORWARD CLUTCH - APPLIED
LO ROLLER CLUTCH - HOLDING

When the selector lever is moved to the Drive (D) position, the manual valve is repositioned to allow line pressure to enter the Drive 4 (D4) passage. Drive 4 oil then flows to the following:
1. Forward Clutch
2. Governor Assembly
3. 1-2 Shift Valve
4. Accumulator Valve

BASIC CONTROL

Drive 4 oil is directed to the forward clutch where it acts on the clutch piston to apply the forward clutch.

Drive 4 oil is directed to the 1-2 shift valve. Drive 4 oil is directed to the accumulator valve and is regulated to a pressure called accumulator pressure; this pressure is directed to the 1-2 and 3-4 accumulator pistons to act as a cushion for the band and fourth clutch apply.

Drive 4 oil is orificed into the governor passage, and is regulated to a variable pressure called governor pressure. Governor pressure increases with vehicle speed and acts against the 1-2, 2-3, 3-4, converter clutch shift valves, and the 3-2 control valve.

In first gear, there could be sufficient throttle valve plunger travel to increase Throttle Valve (T.V.) pressure enough to open the Modulated Throttle Valve (M.T.V.) up and the M.T.V. down valves. In first gear, M.T.V. up exerts pressure against governor pressure at the 1-2, 2-3, 3-4, and converter clutch throttle valves. M.T.V. down pressure is stopped by a land at each of the throttle valves.

SUMMARY

The converter clutch is released, the overdrive roller clutch is holding, the forward clutch is applied; the transmission is in Drive (D) Range - First Gear.