Jeep XJ. Manual — part 397
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
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AUTOMATIC TRANSMISSION—30RH
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DESCRIPTION AND OPERATION (Continued)
Drive range provides first, second, and third gear
ranges.
CONVERTER DRAINBACK VALVE
DESCRIPTION
The drainback valve is located in the transmission
cooler outlet (pressure) line.
OPERATION
The valve prevents fluid from draining from the
converter into the cooler and lines when the vehicle
is shut down for lengthy periods. Production valves
have a hose nipple at one end, while the opposite end
is threaded for a flare fitting. All valves have an
arrow (or similar mark) to indicate direction of flow
through the valve.
BRAKE TRANSMISSION SHIFT INTERLOCK
MECHANISM
DESCRIPTION
The Brake Transmission Shifter/Ignition Interlock
(BTSI), is a cable and solenoid operated system. It
interconnects
the
automatic
transmission
floor
mounted shifter to the steering column ignition
switch (Fig. 54).
OPERATION
The system locks the shifter into the PARK posi-
tion. The Interlock system is engaged whenever the
ignition switch is in the LOCK or ACCESSORY posi-
tion. An additional electrically activated feature will
prevent shifting out of the PARK position unless the
brake pedal is depressed at least one-half an inch. A
magnetic holding device in line with the park/brake
interlock cable is energized when the ignition is in
Fig. 50 Governor
1 – SEAL RING (PLAIN END)
2 – SEAL RING (HOOK END)
3 – PARK GEAR
4 – GOVERNOR BODY
5 – GOVERNOR VALVE
6 – VALVE SHAFT
7 – E-CLIPS (2)
8 – FILTER
9 – SNAP RING (THIN)
10 – SNAP RING (THICK)
11 – SNAP RING
12 – RETAINER WASHER
13 – GOVERNOR WEIGHT ASSEMBLY
14 – GOVERNOR BODY BOLTS (4)
15 – WASHER
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AUTOMATIC TRANSMISSION—30RH
21 - 125
DESCRIPTION AND OPERATION (Continued)
the RUN position. When the key is in the RUN posi-
tion and the brake pedal is depressed, the shifter is
unlocked and will move into any position. The inter-
lock system also prevents the ignition switch from
being turned to the LOCK or ACCESSORY position
(Fig. 55) unless the shifter is fully locked into the
PARK position.
DIAGNOSIS AND TESTING
AUTOMATIC TRANSMISSION DIAGNOSIS
Automatic transmission problems can be a result of
poor engine performance, incorrect fluid level, incor-
rect linkage or cable adjustment, band or hydraulic
control pressure adjustments, hydraulic system mal-
functions or electrical/mechanical component mal-
functions. Begin diagnosis by checking the easily
accessible items such as: fluid level and condition,
linkage adjustments and electrical connections. A
road test will determine if further diagnosis is neces-
sary.
EFFECTS OF INCORRECT FLUID LEVEL
A low fluid level allows the pump to take in air
along with the fluid. Air in the fluid will cause fluid
pressures to be low and develop slower than normal.
If the transmission is overfilled, the gears churn the
fluid into foam. This aerates the fluid and causing
the same conditions occurring with a low level. In
either case, air bubbles cause fluid overheating, oxi-
dation and varnish buildup which interferes with
valve, clutch and servo operation. Foaming also
causes fluid expansion which can result in fluid over-
flow from the transmission vent or fill tube. Fluid
overflow can easily be mistaken for a leak if inspec-
tion is not careful.
CAUSES OF BURNT FLUID
Burnt, discolored fluid is a result of overheating
which has two primary causes.
(1) A result of restricted fluid flow through the
main and/or auxiliary cooler. This condition is usu-
ally the result of a faulty or improperly installed
drainback valve, a damaged main cooler, or severe
restrictions in the coolers and lines caused by debris
or kinked lines.
(2) Heavy duty operation with a vehicle not prop-
erly equipped for this type of operation. Trailer tow-
ing or similar high load operation will overheat the
transmission
fluid
if
the
vehicle
is
improperly
equipped. Such vehicles should have an auxiliary
transmission fluid cooler, a heavy duty cooling sys-
tem, and the engine/axle ratio combination needed to
handle heavy loads.
Fig. 51 Governor—No Output Shaft Rotation
1 – GOVERNOR PRESSURE
2 – LINE PRESSURE
3 – OUTPUT SHAFT
4 – GOVERNOR
5 – VENT
Fig. 52 Governor—Moderate Output Shaft Rotation
Fig. 53 Governor—High Output Shaft Rotation
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AUTOMATIC TRANSMISSION—30RH
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DESCRIPTION AND OPERATION (Continued)
FLUID CONTAMINATION
Transmission fluid contamination is generally a
result of:
• adding incorrect fluid
• failure to clean dipstick and fill tube when
checking level
• engine coolant entering the fluid
• internal failure that generates debris
• overheat that generates sludge (fluid break-
down)
• failure to reverse flush cooler and lines after
repair
Fig. 54 Ignition Interlock Cable Routing
1 – SHIFT MECHANISM
2 – LOCK-TAB
3 – IGNITION LOCK INTERLOCK
4 – STEERING COLUMN
5 – SOLENOID
6 – WIRE CONNECTOR
7 – LEVER
8 – MOUNT BRACKET
9 – SHIFT CABLE
10 – AUTOMATIC TRANSMISSION
11 – TIE STRAP
12 – PARK/BRAKE INTERLOCK CABLE
Fig. 55 Ignition Key Cylinder Actuation
1 – SLIDER LOCKED
2 – CAM RETURN SPRING
3 – INTERLOCK CABLE
4 – CAM
5 – SLIDER
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AUTOMATIC TRANSMISSION—30RH
21 - 127
DIAGNOSIS AND TESTING (Continued)
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