Diagnosis And Testing; Automatic Transmission Diagnosis; Effects Of Incorrect Fluid Level; Causes Of Burnt Fluid - Jeep cherokee 2000 Service Manual

21 - 126 AUTOMATIC TRANSMISSION—30RH
DESCRIPTION AND OPERATION (Continued)
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
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-
Fig. 53 Governor—High Output Shaft Rotation
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.
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