POWER TRAIN
RT765E-2 SERVICE MANUAL
7-24
Published 9-04-2014, Control # 422-08
TRANSMISSION/TORQUE CONVERTER
Description
The transmission/torque converter assembly is mounted to
the engine and is connected to the front and rear axles by
three drive shafts. The main hydraulic pump and hydraulic
pump number three are mounted on the torque converter.
Theory of Operation
The transmission and torque converter function together and
operate through a common hydraulic system. Therefore, it is
necessary to consider both units in discussing operation.
With the engine running, the converter charging pump draws
oil from the transmission pump through the removable oil
suction screen and directs it through the pressure regulating
valve and oil filter.
The pressure regulating valve maintains pressure to the
transmission control for actuating the direction and speed
clutches. This requires a small portion of the total volume of
oil used in this system. The remaining volume of oil is
directed through the torque converter circuit to the oil cooler
and returns to the transmission for positive lubrication. This
regulator valve consists of a hardened valve spool operating
in a closely fitted bore. The valve spool is spring loaded to
hold the valve in a closed position. When a specific pressure
is achieved, the valve spool works against the spring until a
port is exposed along the side of the bore. This sequence of
events provides the proper system pressure.
After entering the converter housing, the oil is directed
through the reaction member support to the converter blade
cavity and exits in the passage between the turbine shaft and
reaction member support. The oil then flows out of the
converter to the oil cooler. After leaving the cooler, the oil is
directed to a fitting on the transmission. Then, through a
series of tubes and passages, lubricates the transmission
bearings and clutches. The oil then gravity drains to the
transmission sump.
The torque converter consists basically of three elements
and their related parts to multiply engine torque. The engine
power is transmitted from the engine flywheel to the impeller
element through the impeller cover. This element is the
pump portion of the hydraulic torque converter and is the
primary component which starts the oil flowing to the other
components which results in torque multiplication. This
element can be compared to a centrifugal pump, in that it
picks up fluid at its center and discharges at its outer
diameter.
The torque converter turbine is mounted opposite the
impeller and is connected to the output shaft of the torque
converter. This element receives fluid at its outer diameter
and discharges at its center. Fluid directed by the impeller
out into the particular design of blading in the turbine and
reaction member is the means by which the hydraulic torque
converter multiplies torque.
The reaction member of the torque converter is located
between and at the center of the inner diameters of the
impeller and turbine elements. Its function is to take the fluid
which is exhausting from the inner portion of the turbine and
change its direction to allow correct entry for recirculation
into the impeller element.
The torque converter will multiply engine torque to its
designed maximum multiplication ratio when the output shaft
is at zero rpm. Therefore, as the output shaft is decreasing in
speed, the torque multiplication is increasing.
The shift control valve assembly consists of a valve body
with selector valve spools. A detent ball and spring in the
selector spool provides one position for each speed range. A
detent ball and spring in the direction spool provides three
positions, one each for forward, neutral, and reverse.
With the engine running and the directional control lever in
the neutral position, oil pressure from the regulating valve is
blocked at the control valve, and the transmission is in
neutral. Movement of the forward and reverse spool will
direct oil, under pressure, to either the forward or reverse
direction clutch, as desired. When either directional clutch is
selected, the opposite clutch is relieved of pressure and
vents back through the direction selector spool. The same
procedure is used in the speed selector.
The direction or speed clutch assembly consists of a drum
with internal splines and a bore to receive a hydraulically
actuated piston. The piston is oil tight by the use of sealing
rings. A steel disc with external splines is inserted into the
drum and rests against the piston. Next, a friction disc with
splines at the inner diameter is inserted. Discs are alternated
until the required total is achieved. A heavy back-up plate is
then inserted and secured with a snap ring. A hub with OD
splines is inserted into the splines of discs with teeth on the
inner diameter. The discs and hub are free to increase in
speed or rotate in the opposite direction as long as no
pressure is present in that specific clutch.
To engage the clutch, the control valve is placed in the
desired position. This allows oil under pressure to flow from
the control valve, through a tube, to a chosen clutch shaft.
This shaft has a drilled passageway for oil under pressure to
enter the shaft. Oil pressure sealing rings are located on the
clutch shaft. These rings direct oil under pressure to the
desired clutch. Pressure of the oil forces the piston and discs
against the heavy back-up plate. The discs, with teeth on the
outer diameter, clamping against discs with teeth on the
inner diameter, enables the hub and clutch shaft to be locked
together and allows them to drive as a unit.
There are bleed balls in the clutch piston which allow quick
escape for oil when the pressure to the piston is released.
Reference Only
