Chevrolet 10 1971 Series Chassis Service Manual page 312

CLUTCHES AND TRANSMISSIONS 7-36
b. Modulator assembly
improperly installed.
c. Governor cover, gasket and bolts - damaged,
loose, case face leak.
d. Speedo gear - " O" ring damaged.
e. Manual shaft seal - damaged, improperly installed.
f. Line pressure tap plug - stripped, shy sealer
compound.
g. Parking pawl shaft cup plug - damaged, improp­
erly installed.
h. Vent pipe (refer to Item 5).
i . Porous case.
4. FRONT END LEAK
a. Front seal - damaged (check converter pack for
nicks, etc., also for pump bushing moved for­
ward); garter spring missing from pump to con­
verter seal.
b. Pump attaching bolts and seals - damaged, miss­
ing, bolts loose.
c. Converter - leak in weld.
d. Pump " O" ring seal - damaged. (Also check
pump groove and case bore).
e. Porous casting (pump or case).
5. OIL COMES OUT VENT PIPE
a. Transmission over-filled.
b. Water in oil.
c. Pump to case gasket mispositioned.
d. Foreign material between pump and case, or be­
tween pump cover and body.
e. Case - porous, pump face improperly machined.
f. Pump - shy of stock on mounting faces, porous
casting.
L - 2nd Gear - Steady road load at approximately 25 mph
2
Gear
1st
2nd
3rd
3rd
Reverse
CASE POROSITY—REPAIR
Transmission leaks caused by aluminum case porosity
have been successfully repaired with the transmission in
the vehicle by using the following procedure.
1. Road test and bring the transmission to operating
temperature.
2. Raise the car and, with the engine running, locate the
source of the oil leak. Check for leaks in all operat­
ing positions.
The use of a mirror will be helpful in
NOTE:
finding leaks.
3. Shut off engine and thoroughly clean area with a
solvent and air dry.
4. Using the instruction of the manufacturer, mix a suf­
ficient amount of epoxy cement, part
make the repair.
" O"
ring seal - damaged or
Selector Lever Position
Drive
(" Zero" throttle to full throttle)
Drive Range, Zero Throttle at 30 mph
Rev. (Zero to full throttle)
#1360016, to
5. While the transmission is still hot, apply the epoxy
to the area, making certain that the area is fully
covered.
6. Allow epoxy cement to dry for three hours and re­
test for leaks, as outlined in Steps 1 and 2.
While road testing with the transmission oil pres­
sure gauge attached and the vacuum modulator tube
connected, the transmission pressures should check
approximately as shown on chart.
OIL PRESSURE CHECK
W ith Vehicle Stationary
1. Oil Pressure Check - Road or Normal Operating
Conditions
Transmission oil pressure gauge and engine tachome­
ter should be connected and the oil pressures should
check as follows:
Approximate
Altitude of Check Neutral
(Ft. above seal level)
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
Minimum
145 psi
Minimum
60
60
95
2. Pressures indicated below are 0 output speed with
the vacuum modulator tube disconnected and with
engine at 1200 rpm.
Pressures are not significantly affected
NOTE:
by altitude or barometric pressure when the
vacuum tube is connected.
3. Pressures indicated below are with the vacuum tube
connected for normal modulator operation, and with
sufficient engine speed to stabilize pump pressure
(approx. 1000 rpm).
Drive, Neutral, Park
60
TURBO HYDRA-MATIC 4 0 0 MODULATOR
ASSEMBLY D IAGN OSIS
After thorough investigation of field returned modulator
assemblies, it has been found that over 50% of the parts
Drive LI
or
Park L2 Reverse
244
150 150
150 150 233
150 222
145
212
138 150
203
132 150
194
126 150
150 186
121
178
116 150
Maximum
155 psi
Maximum
150
260
LI or L2 Reverse
150 107
10-30 CHEVROLET TRUCK SERVICE MANUAL