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TRANSMISSION AND TRANSFER CASE
DIAGNOSIS AND TESTING (Continued)
Fig. 9 Pressure Test Analysis
WARNING: NEVER ALLOW ANYONE TO STAND
DIRECTLY IN LINE WITH THE VEHICLE FRONT OR
REAR DURING A STALL TEST. ALWAYS BLOCK
THE WHEELS AND FULLY APPLY THE SERVICE
AND PARKING BRAKES DURING THE TEST.
STALL TEST PROCEDURE
(1) Connect tachometer to engine. Position tachom-
eter so it can be viewed from driver's seat.
(2) Drive vehicle to bring transmission fluid up to
normal operating temperature. Vehicle can be driven
on road or on chassis dynamometer, if available.
(3) Check transmission fluid level. Add fluid if nec-
essary.
(4) Block front wheels.
(5) Fully apply service and parking brakes.
(6) Open throttle completely and record maximum
engine speed registered on tachometer. It takes 4-10
seconds to reach max rpm. Once max rpm has
been achieved, do not hold wide open throttle
for more than 4-5 seconds.
CAUTION: Stalling the converter causes a rapid
increase in fluid temperature. To avoid fluid over-
heating, hold the engine at maximum rpm for no
more than 5 seconds. If engine exceeds 2500 rpm
during the test, release the accelerator pedal imme-
diately; transmission clutch slippage is occurring.
(7) If a second stall test is required, cool down
fluid before proceeding. Shift into NEUTRAL and run
engine at 1000 rpm for 20-30 seconds to cool fluid.
STALL TEST ANALYSIS
Stall Speed Too High
If the stall speed exceeds 2500 rpm, transmission
clutch slippage is indicated.
Stall Speed Low
Low stall speed with a properly tuned engine indi-
cate a torque converter overrunning clutch problem.
The condition should be confirmed by road testing. A
stall speed 250-350 rpm below normal indicates the
converter overrunning clutch is slipping. The vehicle
also exhibits poor acceleration but operates normally
once highway cruise speeds are reached. Torque con-
verter replacement will be necessary.
Stall Speed Normal But Acceleration Poor
If stall speeds are normal (1800-2300 rpm) but
abnormal throttle opening is required for accelera-
tion, or to maintain cruise speed, the converter over-
running clutch is seized. The torque converter will
have to be replaced.
Converter Noise During Test
A whining noise caused by fluid flow is normal dur-
ing a stall test. However, loud metallic noises indi-
cate a damaged converter. To confirm that the noise
is originating from the converter, operate the vehicle
at light throttle in DRIVE and NEUTRAL on a hoist
and listen for noise coming from the converter hous-
ing.
AIR TESTING TRANSMISSION CLUTCH AND
BAND OPERATION
Air-pressure testing can be used to check transmis-
sion front/rear clutch and band operation. The test
can be conducted with the transmission either in the
vehicle or on the work bench, as a final check, after
overhaul.
Air-pressure testing requires that the oil pan and
valve body be removed from the transmission. The
servo and clutch apply passages are shown (Fig. 10).
TJ
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