Chevrolet 30 Series 1967 Service Manual page 428

CLUTCHES AND TRANSMISSIONS 7-42
add fluid to bring level up to the full mark on gauge rod.
CAUTION:
If fluid level is too high, fluid may
be aerated by the planet carrier. Aerated fluid
will cause turbulence in the converter which will
result in lost power, lower stall speed and lower
pressures in control circuits.
to full mark, then shut off engine to allow air
bubbles to work out of fluid.
When checking oil level, a burned smell and discolora­
tion indicate burned clutches or bands and the transmis­
sion will have to be removed.
MANUAL LINKAGE
Manual linkage adjustment and the associated neutral
safety switch are important from a safety standpoint. The
neutral safety switch should be adjusted so that the engine
will start in the Park and Neutral positions only.
With the selector lever in the Park position, the park­
ing pawl should freely engage and prevent the vehicle
from rolling. The pointer on the indicator quadrant
should line up properly with the range indicators in all
ranges.
OIL LEAKS
Before attempting to correct an oil leak, the actual
source of the leak must be determined. In many cases
the source of the leak can be deceiving due to ''wind flow"
around the engine and transmission.
The suspected area should be wiped clean of all oil
before inspecting for the source of the leak. Red dye is
used in the transmission oil at the assembly plant and
will indicate if the oil leak is from the transmission.
The use of a "black light" to identify the oil at the
source of leak is also helpful. Comparing the oil from
the leak to that on the engine or transmission dip stick
(when viewed by block light) will determine the source of
the leak.
Oil leaks around the engine and transmission are gen­
erally carried toward the rear of the car by the air
stream . For example, a transmission "oil filler tube to
case leak" will sometimes appear as a leak at the rear
of the transmission. In determining the source of an oil
leak it is most helpful to keep the engine running.
The mating surfaces of servo cover, converter housing,
transmission case and transmission
should be carefully examined for signs of leakage. The
vacuum modulator must also be checked to insure that
the diaphragm has not ruptured as this would allow trans­
mission oil to be drawn into the intake manifold. Usually,
the exhaust will be excessively smoky if the diaphragm
ruptures due to the transmission oil added to the com­
bustion. The transmission case extension rear oil seal
should also be checked. All test plugs should be checked
to make sure that they are tight and that there is no sign
of leakage at these points. The converter underpan should
also be removed. Any appreciable quantity of oil in this
area would indicate leakage at the oil pump square seal
ring, oil pump seal assembly, or oil pump bolt sealing
washers.
BASIC PRESSURE CHECKS
Four basic pressure checks are used fo r diagnosis and
Lower fluid level
case eJrtension
Fig. 4 P G - Pressure Test Plug
operational checks for the Aluminum Powerglide trans­
mission. All checks should be made only after thoroughly
warming up the transmission.
• Wide Open Throttle Upshift Pressure.
• Idle Pressure in "Drive" Range.
• Manual "Low" Range Pressure.
• "Drive" Range Overrun (Coast) Pressure.
It is not recommended that stall tests be conducted
which would result in engine vacuum falling below
Hg.
Pressure gauge hose connections should be made at
the low servo apply (main line) test point (fig. 11PG).
Run the gauge line into the driving compartment by push­
ing aside the mast jacket seal. Tie line out of the way of
the drivers feet and connect to pressure gauge J - 21867.
• Wide Open Throttle Upshift Pressure Check
Refer to the pressure check chart for upshift pressure
points as indicated on the low servo apply (main line)
gauge.
• Idle Pressure in "Drive" Range
In addition to the oil pressure gauges, a vacuum gauge
is needed for this check.
With the parking brake applied and the shift selector
lever in "Drive", low servo apply (main line) pressure
should be as shown on the pressure check chart.
If pressures are not within these ranges, the following
items should be checked for oil circuit leakage:
1. Pressure regulator valve stuck.
2. Vacuum modulator valve stuck.
3. Hydraulic modulator valve stuck.
4. Leak at low servo piston ring (between ring and
bore).
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CHEVROLET TRUCK SERVICE M ANUAL