D-4 - First Gear

With 4L60 (700-R4) Transmissions - 4WD Shown, 2WD Similar:

D-4 - FIRST GEAR

FORWARD CLUTCH - APPLIED
LO ROLLER CLUTCH - HOLDING
FORWARD SPRAG 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 Accumulator, Forward Clutch and Abuse Valve
2. Governor Valve
3. 1-2 Shift Valve
4. Accumulator Valve
5. 3-4 Shift Valve

BASIC CONTROL

Drive 4 oil is directed to the forward clutch accumulator where the #12 checkball seats, routing forward clutch feed through an orifice. This combines with the forward clutch accumulator to cushion the forward clutch apply.

During "Rock Cycle" conditions (stuck in mud or snow and "Rocking" out), an abuse valve routes D4 oil to forward clutch feed oil to quicken the apply of the forward clutch.

Drive 4 oil is directed to the 1-2 and 3-4 shift valves. 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 apply in second gear and overdrive.

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, and the 3-2 control valve springs.

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, and 3-4 valves. M.T.V. down pressure is stopped by a land at the 2-3 and 3-4 throttle valves.

SUMMARY

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