Chevrolet 10 Series 1970, Service Manual

Page: 466 / 671

CLUTCHES AND TRANSMISSIONS 7-36
ro llin g . The pointer on the in d icator quadrant should line
up p ro p e rly with the range indicators in a ll ranges.
OIL LEAKS
B e fo re attem pting to c o r r e c t an o il leak, the actual
source of the leak must be determ ined. In many cases the
source of the leak can be d eceivin g due to "w in d flo w ”
around the engine and tran sm ission .
The suspected a rea should be wiped clean of a ll oil
b efo re inspecting fo r the sou rce of the leak. Red dye is
used in the tran sm ission o il at the assem bly plant and
w ill indicate if the o il leak is fr o m the transm ission.
The use of a "b la c k l i g h t " * to iden tify the o il at the
source of leak is also helpful. Com paring the o il fro m the
leak to that on the engine o r tran sm ission dip stick (when
view ed by "b la c k lig h t" w ill determ in e the source of the
leak.
O il leaks around the engine and tran sm ission are
g e n e ra lly c a rrie d tow ard the r e a r of the car by the air
stream . F o r exam ple, a tran sm ission " o i l f ilt e r tube to
case le a k " w ill som etim es appear as a leak at the re a r
of the transm ission. In d eterm in in g the source of an o il
leak it is m ost helpful to keep the engine running.
The mating su rfaces o f s e r v o co ver, co n verter hous­
ing, tran sm ission case and tran sm ission case extension
should be c a re fu lly exam ined fo r signs of leakage. The
vacuum m odulator must also be checked to insure that
the diaphragm has not ruptured as this would allow tran s­
m ission o il to be drawn into the intake m anifold. Usually,
the exhaust w ill be e x c e s s iv e ly smoky if the diaphragm
ruptures due to the tra n sm ission o il added to the combus­
tion. The tran sm ission case extension re a r o il seal
should also be checked. A ll test plugs should be checked
to make sure that they a re tight and that there is no sign
of leakage at these points. The co n verter underpan should
also be rem oved. Any appreciable quantity of o il in this
a rea would indicate leakage at the o il pump square seal
ring, o il pump seal assem bly, o r o il pump bolt seating
w ashers.
BASIC PRESSURE CHECKS
Four b asic p ressu re checks a re used fo r diagnosis and
operational checks fo r the Aluminum P o w e rg lid e tran s­
m ission. A ll checks should be made only a fte r thoroughly
w arm ing up the transm ission.
• W ide Open T h rottle Upshift P re s s u re .
• Idle P re s s u re in " D r i v e " Range.
• Manual " L o w " Range P r e s s u re .
• " D r i v e " Range O verrun (C oast) P re s s u re .
It is not recom m ended that sta ll tests be conducted
which would result in engine vacuum fa llin g below 10" Hg.
P re s s u re gauge hose connections should be made at the
low s e rv o apply (m ain lin e) test point (fig . 5PG). Run the
gauge line into the d rivin g com partm ent by pushing aside
the mast jacket seal. T ie line out of the way of the
d r iv e r s fe e t and connect to P re s s u re Gauge J - 21867.
• W ide Open T h rottle Upshift P re s s u re Check
R e fe r to the p ressu re check chart fo r upshift p ressu re
points as indicated on the low s e rv o apply (m ain line)
gauge.
• Idle P re s s u re in " D r i v e " Range
In addition to the o il p ressu re gauges, a vacuum gauge
is needed fo r this check.
W ith the parking brake applied and the shift s e le c to r
le v e r in " D r i v e " , low s e rv o apply (m ain lin e) pressu re
should be as shown on the p ressu re check chart.
If p ressu res a re not within these ranges, the follow in g
item s should be checked fo r o il c ircu it leakage:
1. P re s s u re regu lator va lve stuck.
2. Vacuum m odulator va lv e stuck.
3. H ydraulic modulator va lve stuck.
4. Leak at low s e rv o piston rin g (between rin g and
bore).
5. Leak at low s e rv o piston rod (between rod and b ore).
6. Leak at va lve body to case gasket.
7. Leak at va lv e body gaskets.
8. O il pump clearan ces.
9. Check passages in tran sm ission case fo r p orosity.
• Manual " L o w " Range P re s s u re Check
Connect a tachom eter, apply the parking brake, place
the s e le c to r le v e r in " L o w " range, and adjust the engine
speed to 1000 rpm with the car stationary.
Low s e rv o apply (m ain lin e) p ressu re should be as
shown on the p ressu re check chart.
P r e s s u re s not within this range can indicate the fo llo w ­
ing p o s sib ilities:
1. P a r tia lly plugged o il suction screen .
2. Broken o r damaged rin g low s ervo .
3. P re s s u re regu la tor va lve stuck.
4. Leak at va lv e body to case gasket.
5. Leak between va lve body gaskets.
6. Leak at s e rv o center.
7. O il pump clearan ces.
• D riv e Range O verrun (C oast) P re s s u re
W ith the v e h icle coasting in " D r i v e " range at 20-25
M PH with engine vecuum at approxim ately 20" Hg., low
s e rv o apply (m ain lin e) p ressu re should be as shown on
the p ressu re check chart.
* A " B la c k L ig h t" testing unit m ay be obtained fro m s e v e ra l d ifferen t s e r v ic e tool suppliers.
POWERGLIDE BASIC PRESSURE (MAINLINE) CHECKS
Engines
W ide Open
T h ro ttle
Upshift
Idle P re s s u re
In D riv e Range
Manual Low
Range @
1000 R P M
D riv e Range Overrun
(C oast) @ 20-35 M PH
(Approx. 20” H g .)
16” Hg. 10” Hg.
L -6 250 93-113 53-75
83-102
125-138
48-53
L -6 292
93-113 53-75 83-102 125-138 48-53
V -8 308 103-121 53-75 83-102
125-138 48-53
V -8 350 105-121 53-75 83-102
125-138 48-53
CHEVROLET TRUCK SERVICE MANUAL