RAM 1500 Van V8-5.2L VIN Y (1999)
Valve Body: Description and Operation
Hydraulic Control System
OVERVIEW
The hydraulic control system provides fully automatic operation. The system performs five basic functions which are: pressure supply, pressure
regulation, flow control, clutch/band application, and lubrication.
PRESSURE REGULATION
The pressure regulator valve maintains line pressure. The amount of pressure developed is controlled by throttle pressure which is dependent on the
degree of throttle opening. The regulator valve is located in the valve body.
The throttle valve determines line pressure and shift speed. Governor pressure increases in proportion to vehicle speed. The throttle valve controls
upshift and downshift speeds by regulating pressure according to throttle position.
SHIFT VALVE FLOW CONTROL
The manual valve is operated by the gearshift linkage and provides the operating range selected by the driver.
The 1-2 shift valve provides 1-2 or 2-1 shifts and the 2-3 shift valve provides 2-3 or 3-2 shifts.
The kickdown valve provides forced 3-2 or 3-1 downshifts depending on vehicle speed. Downshifts occur when the throttle is opened beyond
downshift detent position. Detent is reached just before wide open throttle position.
The 2-3 valve throttle pressure plug provides 3-2 downshifts at varying throttle openings depending on vehicle speed.
The 1-2 shift control valve transmits 1-2 shift pressure to the accumulator piston. This controls kickdown band capacity on 1-2 upshifts and 3-2
downshifts.
The 3-4 shift, quick fill, and timing valves plus the 3-4 accumulator, are only actuated when the overdrive solenoid is energized. The solenoid contains
a check ball that controls a vent port to the 3-4 valves. The check ball either diverts line pressure away from or directly to the 3-4 valves.
The limit valve determines maximum speed at which a 3-2 part throttle kickdown can be made. On transmissions without a limit valve, maximum
speed for a 3-2 kickdown is at detent position.
The 2-3 shuttle valve has two functions. The first is fast front band release and smooth engagement during lift-foot 2-3 upshifts. The second is to
regulate front clutch and band application during 3-2 downshifts.
The 3-4 timing valve is moved by line pressure coming through the 3-4 shift valve. The timing valve holds the 2-3 shift valve in an upshift position.
The purpose is to prevent the 2-3 valve from up or downshifting before the 3-4 valve.
The 3-4 accumulator is mounted on the overdrive housing and performs the same function as the 2-3 accumulator; it is used to smooth engagement
during a 3-4 shift.
The switch valve directs fluid apply pressure to the converter clutch in one position and releases it in the opposite position. It also directs oil to the
cooling and lube circuits. The switch valve regulates oil pressure to the torque converter by limiting maximum oil pressure to 130 psi.
