Jeep Cherokee 2000 Service Manual - page 1424
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.
LOW/REVERSE (REAR) SERVO
While in the de-energized state (no pressure
applied), the piston is held up in its bore by the pis-
ton spring. The plug is held down in its bore, in the
piston, by the plug spring. When pressure is applied
to the top of the piston, the plug is forced down in its
bore, taking up any clearance. As the piston moves, it
causes the plug spring to compress, and the piston
moves down over the plug. The piston continues to
move down until it hits the shoulder of the plug and
fully applies the band. The period of time from the
initial application, until the piston is against the
shoulder of the plug, represents a reduced shocking
of the band that cushions the shift.
GOVERNOR
DESCRIPTION
The governor (Fig. 50) valve body is attached to
the output shaft of the transmission.
OPERATION
The governor meters hydraulic pressure (Fig. 51), and
this metered pressure is used to signal the transmission
when it is time for a shift to occur. It does this by bal-
ancing governor pressure on one side of a shift valve,
and throttle pressure on the other. When governor pres-
sure increases far enough to overcome the throttle pres-
sure on the valve, a shift occurs.
With the gearshift selector in a forward driving
range, line pressure flows from the manual valve and
down to the governor valve. When the output shaft
starts to rotate with vehicle motion (Fig. 52), the gov-
ernor weight assembly will start to move outward
due to centrifugal force. As the weight is moved out-
ward, it will pull the valve with it until the land of
the valve uncovers the line pressure port. As the port
begins to become uncovered, governor pressure is
metered. As the vehicle’s speed continues to increase
(Fig. 53), the weight assembly will be at a point at
which governor pressure is acting on the left side of
the reaction area of the valve. This produces suffi-
cient force to compress the spring and allow the
outer weight to move out against the outer governor
body retaining ring. At a very high speed, the gover-
nor valve will be opened as far as possible. In this
condition, it is possible for governor pressure to meet,
but not to exceed, line pressure. Generally governor
pressure ranges from 0–100 psi from idle to maxi-
mum
speed,
and
rises
proportionally
with
the
increase in output shaft speed. Governor pressure
and throttle pressure are acting upon the shift valves
to determine when a shift will occur. Governor pres-
sure is a direct indication of road speed, and throttle
pressure is an indication of engine load. When both
parameters have been met by the throttle and gover-
nor pressures, an upshift or downshift will occur.
GEARSHIFT MECHANISM
DESCRIPTION
The shift mechanism is cable operated and pro-
vides six shift positions. The shift indicator is located
on the console next to the gear shift. The shift posi-
tions are:
•
Park (P)
•
Reverse (R)
•
Neutral (N)
•
Drive (D)
•
Manual Second (2)
•
Manual Low (1)
OPERATION
Manual low (1) range provides first gear only. Over
run braking is also provided in this range. Manual
second (2) range provides first and second gear only.
Fig. 49 Front Servo
1 – VENT
2 – INNER PISTON
3 – PISTON
4 – SPRING
5 – RELEASE PRESSURE
6 – APPLY PRESSURE
7 – PISTON ROD
21 - 124
AUTOMATIC TRANSMISSION—30RH
XJ
DESCRIPTION AND OPERATION (Continued)