Chevrolet Light Duty Truck 1973, Service Manual

Page: 678 / 979

7 A - 3 6 A U T O M A T IC T R A N S M IS S IO N
h. Vent pipe (refer to item 5).
i. Porous casting. See Subparagraph C.
4. Leak at Front of Transmission.
a. Front pump seal leaks.
1. Seal lip cut. Check converter hub, etc.
2. Bushing moved and damaged, Oil return
hole plugged.
3. No oil return hole.
b. Front pump attaching bolts loose or bolt washer
type seals damaged or missing.
c. Front pump housing "O" ring damaged or cut.
d. Converter leak in weld area.
e. Porous casting (pump).
5. Oil Comes Out Vent Pipe.
a. Transmission over-filled.
b. Water in oil.
c. Foreign material between pump and case or
between pump cover and body.
d. Case - porous near converter bosses. Front
pump cover or housing oil channels shy or stock
near breather. See Subparagraph C.
e. Pump to case gasket mis-positioned.
OIL PRESSURE CHECK
While vehicle is stationary (service brake on), engine
speed set to 1200 rpm, transmission oil pressure gauge
attached, and vacuum modulator tube disconnected, the
transmission line should check as shown in Figure 31M.
While vehicle is stationary (service brake on), engine
speed set to maintain 12 inches hg absolute manifold
pressure, transmission oil pressure gauge attached, and
vacuum modulator tube connected, the transmission line
should check as shown in Figure 32M.
CASE POROSITY REPAIR
External oil leaks caused by case porosity can be
Fig. 31M—Oil Pressure Check
Approximate
Altitude of Check
(Ft. Above Sea Level)
Relative
Engine
Vacuum
(” Hsg.)
250 L-6
307 V-8
&
350 V-8
Drive
Neutral
Park
LI
or
L2
Reverse
Drive
Neutral
Park
LI
or
L2
Reverse
0 13.92 55 79 84 85 105 129
2000 11.83 63
85 96 88
108 134
4000 9.86 72 91 109 91
110 138
6000 7.96 79 97 120 94 112 142
8000 6.23 86 102 131 96 113 146
Fig. 32M—Oil Pressure Check
successfully repaired with the transmission in the vehicle
by using the following recommended procedures:
1. Road test and bring the transmission to operating
temperature, approximately 180 degrees F.
2. Raise vehicle on a hoist or jack stand, engine
running, and locate source of oil leak. Check for oil
leaks in Low, Drive, and Reverse.
3. Shut engine off and thoroughly clean area to be
repaired with a suitable cleaning solvent and a
brush - air dry.
A clean, dry soldering acid brush can be used to
clean the area and also to apply the epoxy cement.
4. Using instructions of the manufacturer, mix a
sufficient amount of epoxy to make the repair.
Make certain the area to be repaired is fully
covered.
5. Allow cement to cure for 3 hours before starting
engine.
6. Road test and check for leaks.
VACUUM MODULATOR DIAGNOSIS
A defective vacuum modulator can cause one or more of
the following complaints.
1. Harsh upshifts and downshifts.
2. Delayed upshifts.
3. Soft upshifts and downshifts.
4. Slips in low, drive and reverse.
5. Transmission overheating.
6. Engine burning transmission oil.
If any one of the above complaints are encountered,
the modulator must be checked.
Vacuum Diaphragm Leak Check
Insert a pipe cleaner into the vacuum connector pipe as
far as possible and check for the presence of
transmission oil. If oil is found, replace the modulator.
Gasoline or water vapor may settle in the vacuum side of
the modulator. If this is found without the presence of
Approximate
Altitude of Check
(Ft. Above Sea Level)
250 L-6
307 V-8
&
'350 V-8
Drive LI Drive LI
Neutral or Reverse Neutral or Reverse
Park L2 Park L2
0
173 166 262 167 166 254
2000 163 159 248 158 159 240
4000 154
152
254
149 152 226
6000 146 146 221 141 146 213
8000 138 141 210 133 140 202
LIGHT DUTY TRUCK SERVICE MANUAL