TRUCK SERVICE MANUAL
TRANSMISSION
HT 700D SERIES TRANSMISSIONS
Para 2-28
NEUTRAL
Fig. 2-8. Neutral torque path
b. Lockup Operation.
Power is transmitted
2-28. TORQUE PATHS THROUGH TRANSMISSION
mechanically through the lockup clutch. Application of
Power is transmitted
a. Converter Operation.
the lockup clutch occurs automatically in selected ranges
hydraulically through the torque converter. The engine
as a function of governor pressure. When the lockup
drives the converter pump. The pump throws oil against
clutch is applied, the converter elements rotate as a unit
the vanes of the turbine, imparting torque to the
at engine speed. This provides a direct drive from the
converter turbine shaft. From t h e turbine, oil flows
engine to the turbine shaft.
Lockup operation is
between the vanes of the stator, and re-enters the pump
illustrated in fourth and fifth gear operation.
where the cycle begins again. When the engine is idling,
impact of the oil upon the turbine blades is negligible.
c. Neutral Operation (fig. 2-8). Engine torque is
When the engine is accelerated, the impact is increased
transmitted through the torque converter as described in
and the torque directed through the turbine shaft can
a, above. The forward clutch is not engaged. Thus the
exceed the engine torque (by an amount equal to the
torque is not transmitted beyond the fourth-clutch hub.
torque ratio of the converter). Converter operation is
(Although the low clutch is applied, two clutches must be
illustrated in first, second, third and reverse operation
applied to produce or reverse.) output shaft rotation in
where it is most likely to occur.
either forward
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