governor pressure has dropped to a lower valve as drive oil is
trying to hold the valve in the shifted position. The valve will
not downshift until modulator oil force and spring force equal
drive oil force and governor oil force. It is for this reason that
downshifts occur at a lower vehicle speed.
Detent Valve and Pressure Regulator Operation
The detent pressure regulator valve receives mainline oil
and regulates it to a maximum of 80 psi. Detent and modu
lator oil pressures are both directed to the detent valve and
redirected according to throttle angle.
When the valve is in the closed or slightly open position, as
shown in figure 24M detent oil is closed off and modulator oil
is directed to one land of both shift control valves. Of course,
it must be recalled that as the throttle is opened modulator
pressure and therefore control pressure increases. As the
detent valve opens further to detent touch, another passage
opens to allow more modulator oil to be sent to another land
on the 2-3 shift valve, detent oil is still closed off.
As the valve is moved through full detent, detent oil is now
directed to an additional land on both shift control valves to
further extend the shift points.
Knowing that modulator pressure is influenced by gover
nor pressure, the transmission could reach a point where
modulator pressure would be reduced to less than 80 psi, even
at full throttle. This is prevented by detent oil unseating the
check ball and filling the modulator passage when modulator
pressure becomes less than 80 psi detent oil pressure. Modu
lator pressure is then a constant 80 psi.
Position-Manual Low Control Valve Operation
The manual low control valve (fig. 25M) is used to prevent
first gear engagement at too high a vehicle speed. This valve is
Fig. 25M-Manual Low Control Valve
pushed to the right and blocks low oil pressure if governor
pressure is too high. The pressure exists in low to increase
mainline pressure and prevent a 2-3 upshift.
Low oil pressure is routed to the 1-2 shift valve between
the valve segments preventing a 1-2 upshift by holding the left
portion in the first speed position. The low clutch is applied
by the right portion of the 1-2 shift valve being to the right
Two clutches are applied to achieve reverse gear, low
reverse clutch and direct. The full piston areas are used in
Fig. 24M-Detent Valve