RAM 1500 Van V8-5.9L VIN Z LDC (2001)
Band Apply Servo: Description and Operation
32RH (A-999) 3 Speed
Front Servo
FRONT SERVO
DESCRIPTION
The kickdown servo (Fig. 95) consists of a two-land piston with an inner piston, a piston rod and guide, and a return spring. The dual-land piston uses
seal rings on its outer diameters and an O-ring for the inner piston.
OPERATION
The application of the piston is accomplished by applying pressure between the two lands of the piston. The pressure acts against the larger lower land
to push the piston downward, allowing the piston rod to extend though its guide against the apply lever. Release of the servo at the 2-3 upshift is
accomplished by a combination of spring and line pressure, acting on the bottom of the larger land of the piston. The small piston is used to cushion
the application of the band by bleeding oil through a small orifice in the larger piston. The release timing of the kickdown servo is very important to
obtain a smooth but firm shift. The release has to be very quick, just as the front clutch application is taking place. Otherwise, engine runaway or a
shift hesitation will occur. To accomplish this, the band retains its holding capacity until the front clutch is applied, giving a small amount of overlap
between them.
Pistons
DESCRIPTION
There are several sizes and types of pistons used in an automatic transmission. Some pistons are used to apply clutches, while others are used to apply
bands. They all have in common the fact that they are round or circular in shape, located within a smooth walled cylinder, which is closed at one end
and converts fluid pressure into mechanical movement. The fluid pressure exerted on the piston is contained within the system through the use of
piston rings or seals.
OPERATION
The principal, which makes this operation possible is known as Pascal's Law. Pascal's Law can be stated as: "Pressure on a confined fluid is
transmitted equally in all directions and acts with equal force on equal areas."
PRESSURE
