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Fig. 14PG-Governor and Governor
booster valve. Continued motion to the right uncovers an
exhaust for the booster valve oil. This exhaust port is located
in the manual valve bore and will be covered in detail in
following descriptions. Spools 2 and 3. Spool 3 is larger than
spool 2, thus governor pressure tends to move the valve to the
right, reducing modulator pressure to the booster valve. This
application of governor pressure results in smoother part
throttle upshifts by reducing mainline pressure.
A summary of the modulator's action shows that it helps
tailor mainline pressure to meet changing requirements. It does
this by varying booster pressure in relation to; modulator
spring pressure, engine vacuum, governor pressure, and main
line pressure itself.
to the governor where it is re-regulated and delivered to the
low-drive shift valve, the vacuum modulator valve and the rear
face of the downshift timing valve (fig. 14PG). As the governor
rotates with the output shaft, the inner and outer weights
throw outward due to centrifugal force. The governor valve,
connected by a small through-shaft to the weights, is pulled
inward, opening the mainline delivery port. Mainline pressure
enters the open port and becomes governor pressure. This pres
sure, while acting on the various control valves, applies force
to the flat area of the large governor spool. When governor
pressure overcomes the centrifugal force of the weights, the
valve moves outward and closes the mainline feed to the
governor circuit.
At lower speeds, when centrifugal force is reduced, hy
draulic pressure moves the governor valve further outward,
opposing the pull of the weights, and opens the governor pres
sure to exhaust. As the hydraulic pressure drops, the pull of
the weights returns the valve and regulates governor pressure in
direct relation to road speed.
Automatic Upshift
As the vehicle is moving in automatic low range, spring
pressure plus throttle valve pressure on the low-drive shift
valve holds the valve in a position that blocks mainline pres
sure to the high clutch apply. To provide an automatic upshift,
governor pressure is delivered to the shift valve opposing spring
pressure (fig. 15PG). As governor pressure overcomes the
spring force, the shift valve moves to the right and allows
mainline pressure to enter the high clutch apply-low servo
release circuit.
NOTE: Throttle valve pressure acts on the shift valve and
the regulator to oppose governor pressure.
HYDRAULIC UNIT OPERATION
Manual Valve
A manual control valve (Fig. 13PG) in the transmission
valve body routes oil to the controlling devices that govern
operation in Drive, Manual Low and Reverse. In Neutral or
Park ranges, this control valve cuts off oil pressure to the band
and clutch and exhausts it into the sump. The manual valve is
moved into position for the desired range by the driver using
the selector lever on the steering column or console.
Drive Range
When the manual valve is moved to the "D" position, it
opens passages to direct mainline pressure to the low-drive
shift valve, the high speed downshift timing valve, and the low
servo apply. Mainline pressure enters the timing valve bore
between the spools and passes through both the opening and
the restricting orifice to charge the low servo apply. Spring
pressure holds the shift valve in the full left position which
blocks the clutch apply passage and thus allows the servo to
apply the low band.
The transmission is now in automatic low range with the
low sun gear held stationary.
Governor
Oil pressure in the high clutch apply-low servo release cir
cuit is routed to passages in the oil pump (fig. 16PG). The high
clutch apply oil is delivered to the clutch drum in the area
between two seal rings on the pump cover hub. This pressure
acts on the high clutch piston, causing it to engage the plates
which lock the clutch to the input shaft. Since one sun gear is
Fig. 15PG-Low-Drive Shift
