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7-42
GROUP 7-AUTOMATIC TRANSMISSION
assembly spring force would be
required.
If pressure readings are low, and
line pressure does not start to build
up until vacuum drops to 15
inches,
an adjustment to increase diaphragm
spring force is required.
To increase control pressure, tum
the adjusting screw in clockwise. To
reduce control pressure, back the
adjusting screw out by turning it
counterclockwise.
One complete turn of the adjust-
ing screw (360.) will change idle line
control pressure approximately
2-
3
psi. After adju stment is
made,
install
the vacuum line and recheck the
pressures, part icularly the pressure
at 10 inches of
vacuum.
The diaphragm should not be
adjusted to provide pressures below
the ranges previously specified in
order to change shift feel. To do so
could result in soft or slipping shifts
and damage to the transmission.
STALL TEST
•
Start the engine to allow it to
reach its normal
temperature. Apply
both the parking and service brakes
while making tests.
The stall test is made in D, 2 and I,
or R, at full throttle to check engine
performance, converter clutch
oper-
ation or installation, and the hold-
ing ability of the forward
clutch,
reverse-high clutch and low-reverse
band and the gear train one-way
clutch.
While making this test, do
not hold the throttle open for more
than five seconds at a time. Then
move the selector lever to Neutral
and run engine at l 000 rpm for
about 15 seconds to cool the con-
verter before making the next test.
If the engine speed recorded by the
tachometer exceeds the maximum
limits specified in Table 2 release
the accelerator immediately because
clutch or band slippage is
indicated.
TABLE 2- Stall Speed Limits
Engine
Engine
Trans-
Model
Speed
mission
CID
(rpm)
Type
302-2V
1780-2000
C4
351-2V
1520-1720
C4
250-2V
1650-1850
C4
250-1V
1600-1800
C4
STALL SPEED TOO HIGH
If stall speed exceeds specifica-
tions, band or clutch slippage is in-
dicated, depending on transmission
selector lever position
.
Excessive
engine rpm only in
D,
2 and
I,
indicates forward clutch slippage.
Excessive engine rpm only in R
indicates either reverse-high clutch
or low-reverse band
slippage.
Exces-
sive engine rpm only in D indicates
gear train one-way clutch slippage.
STALL SPEED TOO LOW
When the stall test speeds are low
and the engine is properly tuned,
converter stator clutch problems are
indicated.
A road test must be
performed to determine the exact
cause of the trouble.
If the stall test speeds are 300 to
400 rpm below the specifications
shown in Table 2 and the car cruises
properly but has very poor accelera-
tion,
the converter stator clutch is
slipping.
If the stall test speeds are 300 to
400 rpm below the specified values,
and the car drags at cruising speeds
and acceleration is poor, the stator
clutch could be installed backwards.
Remove the converter and check
the stator clutch as described in
Cleaning and Inspection.
When the stall test shows normal
speeds, the acceleration is good, but
the car drags at cruising speeds, the
difficulty is due to a seized stator
assembly. If the stator is
defective,
replace the converter.
INITIAL ENGAGEMENT
CHECKS
Initial engagement checks are
made to determine if initial band
and clutch engagements are smooth.
Run the engine until its normal
operating temperature is reached.
With the engine at the correct idle
speed, shift the selector lever from
N to D, 2 and I, and R. Observe
the initial band and clutch engage-
ments. Band and clutch engage-
ments should be smooth in all
positions. Rough initial engagements
in D, 2 and 1, or R are caused by
high engine idle speed or high
control
pressures.
SHIFf POINT CHECKS
Check the light throttle upshifts
in D. The transmission should start
in first gear, shift to second, and
then shift to third within the shift
points specified in the specifications
section.
While the transmission is in third
gear, depress the accelerator pedal
through the detent (to the floor).
The transmission should shift from
third to second or third to first,
depending on the car speed.
Check the closed throttle down-
shift from third to first by coasting
down from about 30 mph in third
gear.
The shift should occur within
the limits specified in the specifica-
tions section.
When the selector lever is at 2,
the transmission can operate only
in second.
With the transmission in third
gear and road speed over 39 mph,
the transmission should shift to
second gear when the selector lever
is moved from D to I. The trans-
mission will downshift from second
or third to first gear when this same
manual shift is made below ap-
proximately 38 mph. This check will
determine if the governor pressure
and shift control valves are function-
ing properly.
During the shift check operation,
if the transmission does not shift
within specifications or certain gear
ranges cannot be obtained, refer to
the Diagnosis Guide page
7-
44 to
resolve the
problem.
AIR PRESSURE CHECKS
A NO DRIVE condition can
exist, even with correct transmission
fluid pressure, because of inopera-
tive clutches, bands. The inopera-
tive units can be located through a
series of checks by substituting air
pressure for the fluid pressure to
determine the location of the
malfunction.
When the selector lever is at 2,
a NO DRIVE condition may be
caused by an inoperative forward
clutch or intermediate band. A NO
DRIVE condition at D may be
caused by an inoperative forward
clutch or one-way clutch. When
there is no drive in I the difficulty
could be caused by improper func-
tioning of the forward clutch or
low-rev~rse
band and the one-way
clutch
.
The low-reverse band cannot be
checked in
I.
If the low-reverse
band or clutch fails
,
the one-way
clutch will hold the gear train and
operation will be normal except
that there will be no engine braking.
Failure to drive in reverse range
could be caused by a malfunction
of the reverse-high clutch or low-
reverse band. Erratic shifts could be
caused by a stuck governor valve.
To make the air pressure checks,
drain the transmission fluid, and
then remove the oil pan and the
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