Advertisement
PART 7-2- C4 AUTOMATIC TRANSMISSION
7-41
should
be
checked in all ranges ex-
cept Park and Neutral. Shift the
transmission into D, 2, and R, and
check control pressure increase in
each range. With the correct con-
trol ptessure at engine idle, advance
the throttle until the engine vacuum
reading
is
approximately
17.0
inches. As the vacuum gauge read-
ing decreases into these specifica-
tions, the control pressure should
start to increase.
Control pressure increase may
be
noted immediately when the throttle
is opened due to the increased pump
output, resulting from increased
engine rpm. When this happens, the
pressure increase point can be
checked by using a distributor
vacuum tester. Install the dis-
tributor tester vacuum line on the
diaphragm assembly. Adjust the
tester to provide over 18 inches of
vacuum. Increase the engine to
600-
700
rpm.
Adjust the tester vacuum
reading to approximately 17.0 in-
ches and observe the transmission
pressure gauge for the pressure
increase.
TEST NUMBER
3-
CONTROL PRESSURE CHECK
AT 10 INCHES OF VACUUM
A control pressure check should
be
made at 10 inches of vacuum in
D, 2. Advance the throttle until the
engine vacuum reading is 10 inches
and check the control pressure re-
gulation. Control pressure should
be
as shown in Table 1.
TEST NUMBER
~
CONTROL PRESSURE CHECK
AT 3 INCHES OF VACUUM-
Check control pressure at one
inches of vacuum in D, 2, and 1.
The control pressure should be as
shown in Table l. Then move the
selector lever to
R.
With the
vacuum at one inch the control
pressure should be as shown in
Table I.
While making this pressure test,
do not hold the throttle open for
more than five seconds in each
detent position. Between each test-
move the selector lever to neutral
and run the engine at I 000 rpm for
fifteen seconds to cool the converter.
If the vacuum and pressure gauge
readings are within specifications,
the diaphragm unit and transmission
control pressure regulating system
are operating properly.
If the transmission control pres-
sure is too low, too high, fails to
rise with throttle opening, or is
extremely erratic, use the procedure
given under the following appropri-
ate heading to resolve the problem.
CONTROL PRESSURE
TEST RESULTS
TEST NUMBER I -
CONTROL PRESSURE IS LOW
AT ENGINE IDLE
If control pressure at engine idle
is low in all selector lever positions,
trouble other than the diaphragm
unit is indicated.
When control pressure at engine
idle is low in all ranges, check for
excessive leakage in the front oil
pump, case, and control valve body,
or a
sticking control
pressure
regulator valve.
TEST NUMBER I -
CONTROL PRESSURE IS
HIGH AT ENGINE IDLE
If transmission control pressure
at engine idle is too high in all
ranges, the trouble may be in the
diaphragm unit or its connecting
vacuum tubes and hoses, throttle
valve, or control rod.
With the engine idling, discon-
nect the hose from the diaphragm
unit and check the engine manifold
vacuum. Hold a thumb over the
end of the hose and check for
vacuum. If the engine speeds up
when the hose is disconnected and
slows down as the thumb is held
against the end of the hose, the
vacuum source is satisfactory.
Stop the engine, and remove the
diaphragm unit and the diaphragm
unit control rod. Inspect the control
rod for a bent condition and for
corrosion. Check the diaphragm
unit for leakage with the distributor
tester.
TEST NUMBER 2-
CONTROL PRESSURE DOES
NOT INCREASE WITH
VACUUM AT
APPROXIMATELY 17.0 INCHES
When the control pressure is
within specifications at engine idle,
but does not increase as the vacuum
is decreased to the specified limits,
first check the control rod between
the vacuum unit and throttle valve
for proper engagement. If the con-
trol rod is not assembled into the
end of the throttle valve or vacuum
unit, the valve cannot regulate
throttle pressure to increase con-
trol pressure. Next check for a stuck
primary throttle valve, pressure
booster valve, or a stuck control
pressure regulator valve.
If control pressure increases
be-
fore or after vacuum is decreased
to approximately 17.0 inches, check
for a leaking diaphragm assembly,
bent diaphragm can, or worn or
bent control rod.
TESTS NUMBER 3 AND
~
CONTROL PRESSURE NOT
WITHIN LIMITS AT 10 OR 1
INCHES OF VACUUM
If idle pressure and pressure point
increase are within specifications
but pressures at 10 or 1 inch of
vacuum on the transmission is not
within specification in all
ranges,
excessive leakage, low pump capa-
city, or a restricted oil pan screen
is indicated.
If pressures are not within speci-
fications for specific selector lever
positions only, this indicates exces-
sive leakage in the clutch or servo
circuits used in those ranges.
FIG. 8- Adiustable Vacuum Unit
When the control pressure is
within specifications at engine idle,
but not within specifications at the
pressure rise point of approximately
17.0 inches of vacuum, at 10 inches
of vacuum, or at 1 inch of
vacuum,
the vacuum diaphragm unit may
need adjustment.
The vacuum diaphragm assembly
used on the C4 transmission has an
adjusting screw in the vacuum hose
connecting tube (Fig. 8). The inner
end of the screw bears against a
plate which in turn bears against
the vacuum diaphragm
spring.
All readings slightly high or all
readings slightly low may indicate
the vacuum unit needs adjustment
to correct a particular shift con-
dition.
For
example,
if the pressure at
lO inches of vacuum was 120 psi and
the pressure at 1 inch of vacuum
was 170 psi and upshifts and down-
shifts were harsh, a diaphragm
adjustment to reduce the diaphragm
Advertisement
